Patent Application
20230407378
The contents of the electronic sequence listing (960296.04363.xml; Size: 44,097 bytes; and Date of Creation: Nov. 4, 2022) is herein incorporated by reference in its entirety.
The present disclosure generally relates to nucleic acid-scaffolded catalytic systems. The present disclosure further relates to methods of using nucleic acid-scaffolded catalytic systems for applications such as controlling reaction rates, sensing, biomarker detection, protein-protein interaction detection, and proximity labeling.
Catalysts play an important role in the effective and efficient transformation of reactants to intermediates and products. Catalysts are often used to convert readily available (often lower value) starting materials to products that possess more desirable characteristics (e.g., functionality). The creation of catalysts that mimic enzymes through pre-organization of reactive groups is a long-standing goal. In natural enzymes, protein scaffolds hold multiple functional groups in proximity, providing massive rate accelerations that are not observed when the same functional groups are unscaffolded. Catalyst research often focuses on the identification of new catalysts or the optimization of performance to achieve higher conversions and enhanced selectivity. Some researchers have turned their attention to the development of catalysts whose activity is controlled by external stimuli. Such switchable catalysts are of interest in a variety of applications. Catalysts that combine biological functions/cues with synthetic catalysts have the potential to enable or improve a variety of reactions and processes.
While matching the sophistication of enzymes may be an elusive target for synthetic systems, supramolecular enzyme mimics offer a broader palette of functional groups since they are not limited to natural amino acids and cofactors. Impressive catalytic properties have been demonstrated in a variety of enzyme-mimicking supramolecular scaffolds.
An exciting area of recent progress in supramolecular chemistry is the pre-organization of synergistic catalytic reactions. Synergistic catalysis combines two co-catalysts to carry out a reaction that would not be possible using either co-catalyst alone. Examples include a variety of synergistic combinations of transition metal catalysts, photocatalysts, organocatalysts, radical catalysts, and Lewis acid catalysts. In scaffolded synergistic catalysis, the proximity afforded by precise positioning of the co-catalysts accelerates the reaction compared to the unscaffolded reactions, in which the large mean distance between the co-catalysts limits synergistic interactions, often necessitating high catalyst loadings. However, it remains a challenge to fine-tune the spacing of each co-catalyst. Furthermore, previously demonstrated scaffolds for synergistic catalytic reactions are difficult to engineer for stimuli-triggered conformational changes to alter the rate of the reaction. Allostery is an attractive property of enzyme catalysis and is of fundamental interest for enzyme-mimicking systems and for the development of sensors and responsive materials.
Thus, there is a need for designed catalytic systems that provide precise positioning of reactive functional groups and exhibit conformational and catalytic activity switching in response to external stimuli.
Disclosed herein is a nucleic acid-scaffolded catalytic system. In one aspect, the nucleic acid-scaffolded catalytic system includes a nucleic acid catalyst including a first nucleic acid strand and, optionally, a second nucleic acid strand, a first reactive moiety attached to the first nucleic acid strand, and a second moiety attached to the first nucleic acid strand or the second nucleic acid strand, wherein a catalytic activity of the first reactive moiety is dependent on a distance between the first reactive moiety and the second moiety.
A trigger may bind to the nucleic acid structure and trigger an increase in catalytic activity of the first reactive moiety. A ‘trigger’, which may also be referred to as an ‘analyte,’ may bind to either or both of the first nucleic acid strand and the second nucleic acid strand. A trigger may increase or decrease the catalytic activity of the first reactive moiety by altering the distance between the first reactive moiety and the second moiety. The trigger may include an ion, a small molecule, a protein, and a nucleic acid. In certain examples, the trigger may be a single stranded DNA or RNA oligomer that anneals with the first nucleic acid strand or to both of the first nucleic acid strand and the second nucleic acid strand.
In certain examples, the first reactive moiety may be a catalyst. In other examples, the first reactive moiety and the second moiety may be abiotic groups. In certain cases, the first reactive moiety may be attached to the 5′ end of the first nucleic acid strand and the second moiety may be attached to the 3′ end of the first nucleic acid strand. In other cases, the reverse may be true where the first reactive moiety may be attached to the 3′ end of the first nucleic acid strand and the second moiety may be attached to the 5′ end of the first nucleic acid strand.
In certain examples the nucleic acid scaffold the first nucleic acid strand may be folded into a stem-loop structure. The first reactive moiety may be attached to a first end of the first nucleic acid strand and the second reactive moiety may be attached to a second end of the first nucleic acid strand such that the first reactive moiety and the second moiety are in proximity in the stem-loop structure. When a trigger, which may be a template nucleic acid strand, anneals with the first nucleic acid strand, the stem-loop structure may open to move the second moiety farther away from the first reactive moiety.
In certain examples, the nucleic acid-scaffolded catalytic system may include the first reactive moiety attached to the first nuclei acid strand, the second moiety attached to the second nucleic acid strand. When a trigger (that may be a template nucleic acid strand) anneals with the first nucleic acid strand and the second nucleic acid strand, the first reactive moiety may be brought into proximity to the second moiety. In certain cases, a separation of five or more nucleotides between the first reactive moiety and the second moiety diminishes the catalytic activity of the first reactive moiety.
In another example, the first reactive moiety may catalyze the production of a colored or fluorescent product. In certain cases, the first reactive moiety may be a photocatalyst and the second moiety may be a quencher of the photocatalyst. One example may include the photocatalyst Eosin Y and the quencher may be black hole quencher 1. In another example, the photocatalyst may be a ruthenium catalyst and the quencher may be black hole quencher 2. In other examples, the first reactive moiety may be a photocatalyst and the second moiety may be a Forster resonance energy transfer (FRET) donor. In certain cases, the photocatalyst may be a ruthenium complex. In a certain case, the first reactive moiety may be a ruthenium photocatalyst and the second moiety may be a cobalt catalyst, and the ruthenium photocatalyst and the cobalt catalyst synergistically convert tetrahydroisoquinoline to isoquinoline when in proximity to each other. In another example, the first reactive moiety may be an iridium photocatalyst and the second moiety may be a nickel complex, and the iridium photocatalyst and the nickel complex synergistically catalyze a bond-forming reaction when in proximity to each other.
In certain cases, the first reactive moiety and the second reactive moiety may synergistically catalyze a reaction when in proximity to each other.
In other cases, the first reactive moiety may catalyze the conversion of a prodrug into an efficacious drug.
In certain examples, the first reactive moiety may be a palladium complex and the second moiety may be an activating ligand of the palladium complex. The palladium complex may catalyze removal of a propargyl group from a substrate when activated by the activating ligand.
The nucleic acid-scaffolded catalytic system may include a first reactive moiety that may catalyze the formation of a polymer. In some examples, the first reactive moiety may catalyze the polymerization of diaminobenzidine (DAB). The first reactive moiety may catalyze the polymerization of 3,3′-diaminobenzidine. In other examples, the first reactive moiety may catalyze the formation of a cross-linked polymer hydrogel. In certain cases, the first reactive moiety may catalyze poly(ethylene glycol) diacrylate cross-linking to form a hydrogel. In another example, the first reactive moiety may catalyze the synthesis of a controlled polymer, such as a polymer synthesized through Photoinduced electron/energy transfer reversible addition—fragmentation chain transfer polymerization.
An example of the disclosed technology may include the first reactive moiety being 2,2,6,6-tetramethylpiperidiny-1-yl)oxyl (TEMPO) organic radical and the second moiety may be a copper co-catalyst. In this example, the TEMPO organic radical and the copper co-catalyst may catalyze the oxidation of an alcohol to an aldehyde. The TEMPO radical may be attached to the first nucleic acid strand and the copper co-catalyst is attached to the second nucleic acid strand. The analyte may be a template nucleic acid strand that anneals with the first nucleic acid strand and the second nucleic acid strand to bring the TEMPO radical and the copper co-catalyst into proximity. In a further aspect of this example, the catalytic system may further include an invader nucleic acid strand that displaces the template nucleic acid strand and separates the TEMPO radical from the copper co-catalyst. In a certain case, a trigger strand that anneals with one of the first nucleic acid strand and the second nucleic acid strand to separate the first reactive moiety from the second moiety may switching off catalysis of the reaction.
In another aspect, the nucleic acid-scaffolded catalytic system may further include a first split invader construct that includes a first protein binding moiety linked with a nucleic acid strand having a first complementary domain and a first complementary catalyst domain opposite the first protein binding domain and a second split invader construct that includes a second protein binding moiety linked with a nucleic acid strand having a second complementary domain and a second complementary catalyst domain opposite the second protein binding moiety. The first protein binding moiety and the second protein binding moiety may bind to sites on one or more proteins. The first complementary domain and the second complementary domain are complementary to one another and when the first complementary domain and second complementary domain are annealed with each other, the first split invader construct and second split invader construct form a full invader duplex. The full invader duplex may trigger the nucleic acid-scaffolded catalytic system by binding the first complementary catalyst domain and the second complementary catalyst domain of the full invader duplex to either or both of the first nucleic acid strand and the second nucleic acid strand to trigger an increase or a decrease in the catalytic activity of the first reactive moiety by altering the distance between the first reactive moiety and the second moiety.
The first protein binding moiety and the second protein binding moiety may be an aptamer or an antibody.
One aspect of the disclosed technology includes a method for controlling a rate of a reaction with a nucleic acid-scaffolded catalyst, including: triggering a conformational shift in the nucleic acid-scaffolded system according as described earlier by addition of a trigger that binds to the nucleic acid scaffold, the conformational shift in the nucleic acid scaffold changing the rate of the reaction by changing the distance between the first reactive moiety and the second moiety.
One example of this method may involve the first reactive moiety being a photocatalyst and the method further comprises irradiating the photocatalyst.
One aspect of the disclosed technology includes a method for detecting an analyte, involving exposing the nucleic acid scaffold system described above to a sample. If the sample contains the analyte, then the analyte may bind to the nucleic acid scaffold and trigger a conformational shift in the nucleic acid scaffold that changes the distance between the first reactive moiety and the second moiety and the catalytic activity of the first reactive moiety, and detecting the presence of the analyte based on the change in catalytic activity of the first reactive moiety.
Another aspect of the disclosed technology includes a method for detecting a protein-protein interaction. The method includes exposing the nucleic acid-scaffolded system described previously to a sample with the one or more proteins. Trimolecular annealing between the first complementary catalyst domain, the second complementary catalyst domain, and either or both of the first nucleic acid strand and the second nucleic acid strand may trigger a conformational shift that changes the distance between the first reactive moiety and the second moiety and detecting the trimolecular annealing based on the change in catalytic activity of the first reactive moiety. One example of this methods of using the disclosed technology includes detecting photocatalytic labeling. This method may also involve detection of fluorescence.
An example of the immediately preceding method where there are two proteins includes the binding of the first protein to the second protein may lead to an increase or decrease in the catalytic activity of the first reactive moiety. The first protein and the second protein may be extracellular proteins. The extracellular proteins may be two different cell surface antigens, where the first nucleic acid strand and the trigger strand are tethered to respective antibodies for the two different cell surface antigens. The interaction between the first protein and the second protein may be an intercellular protein-protein interaction, a protein-ligand interaction on a cell surface, neuronal proteins at a synaptic cleft, are biomarkers on a same cell (e.g., the biomarkers are biomarkers for circulating tumor cells). In another example, the first reactive moiety may catalyze formation of a magnetic coating on the cell to identify the cell as a circulating tumor cell
In a certain example, the first nucleic acid strand may be conjugated to an antibody and bound to a cell via an interaction between the antibody and an antigen. The trigger nucleic acid strand may be conjugated to an antibody and bound to a cell via an interaction between the antibody and an antigen. One example of this method involves the one or more proteins being located on one or more cell surfaces.
The present disclosure provides switchable nucleic acid-scaffolded catalytic systems and methods of use. These catalytic systems described herein are switchable, i.e., their activity is controlled by an external stimuli. The system may include a nucleic acid catalyst including a first nucleic acid strand, an optional second nucleic acid strand, a first reactive moiety attached to the first nucleic acid strand, and a second moiety attached to either the other end of the first nucleic acid strand or the second nucleic acid strand. In one aspect, the first reactive moiety is attached to one end of the first nucleic acid strand while the second reactive moiety is attached to the other end of the first nucleic acid strand, such that, when the first nucleic acid strand changes confirmation after a stimuli, can be activated or inactivated. The catalytic activity of the first reactive moiety may be dependent on a distance between the first reactive moiety and the second moiety. The system may further include a stimuli, for example, an analyte that binds to either or both of the first nucleic acid strand and the second nucleic acid strand to trigger conformational changes and thus an increase or a decrease in the catalytic activity of the first reactive moiety by altering the distance between the first reactive moiety and the second moiety. Suitable depictions of the nucleic-acid scaffolded catalytic system are illustrated in, for example, in the Figures and Examples described herein.
The switchable nucleic acid-scaffolded catalytic systems of the present invention can be used for a number of different applications and methods as described more herein. For example, the switchable nucleic acid-scaffolded catalytic systems may be used for fluorescent or colorimetric signal amplification for diagnostics as demonstrated in the examples. Further, the switchable nucleic acid-scaffolded catalytic systems can be used for spatially-resolved proteomic mapping. Methods of using the switchable nucleic acid-scaffolded catalytic systems further include the ability to polymerize diaminobenzidine to create contrast for electron microscopy. Further, the switchable nucleic acid-scaffolded catalytic systems may be used for synthesizing polymer coatings on cell surfaces for identification and isolation of rare cell types described more herein.
As used herein, the term “nucleic acid” refers to a polymer of nucleic acid bases such as oligonucleotides including, but not limited to, single-stranded DNA, double-stranded DNA, RNA, aptamers, and peptide nucleic acids (PNAs). The nucleic acid bases may include natural nucleic acid bases (e.g., adenine, guanine, cytosine, thymine), unnatural nucleic acid bases, or combinations thereof. DNA aptamers are about 15-45 nucleotide DNA oligomer that has been selected for its binding affinity toward a molecule of interest, such as, but not limited to, proteins or small molecules.
As used herein, the term “abiotic group” is a functional group that is not derived from a biological or living organism.
As used herein, a “switchable nucleic acid-scaffolded catalytic system” is used interchangeably with “nucleic acid-scaffolded catalytic system” and “nanocatalyst system” and is a nucleic acid-based structure that bears at least one reactive moiety and exhibits a change in conformation in response to an external stimulus. The catalyst is thus able to trigger a chemical reaction and the DNA nanocatalyst change in conformation allows for the triggering and control of the catalytic activity. The conformational change results in a change in the catalytic activity (from catalytically inactive to catalytically active, or from catalytically active to catalytically inactive) by changing a distance between the reactive moiety and another moiety that influences the catalytic activity of the reactive moiety. The reactive moiety is precisely positioned with respect to the influencing moiety in either or both of the catalytically inactive and active states of the system via the structural programmability of the nucleic acid-based structure.
A “nucleic acid-scaffolded catalyst”, “scaffolded catalyst”, or “catalyst” as used herein includes a nucleic acid scaffold formed of one or more nucleic acid strands and bearing at least a first reactive moiety that catalyzes a reaction when activated through a conformational change in the nucleic acid scaffold. Suitable reactive moieties include catalyst known in the art and as described in the Examples. In some embodiments, the catalyst includes a first reactive moiety and a second reactive moiety, wherein the association (or de-association) of the first and second moiety results in the catalytic activity. In some embodiments, the distance between the first catalytic moiety and second catalytic moiety can control the rate of the reaction of the catalytic reaction.
A “nucleic acid scaffold” as used herein includes one or more nucleic acid strands having a defined structure to which one or more reactive moieties having catalytic activity are attached. The nucleic acid scaffold is designed to undergo a conformational change in response to external stimuli, such as analyte binding. In one embodiment, the individual molecular beacon/hairpin and anchor components are between 30 and 55 nucleotides long, and when they hybridize together will emulate a single stand of DNA that is about 80-90 nucleotides long (accounting for double stranded portions that are annealed). In some examples, the trigger strands are equivalent to 30-100 nucleotides long. In some studies with simpler templates, only one strand of DNA (e.g. Biotin/SAV system), the molecular beacon/hairpin can be about 43 nucleotides, and the triggers are 25-43 nucleotides long.
As used herein, an “analyte” or “trigger” may be a chemical substance that binds the nucleic acid-scaffolded catalyst to induce a conformational change that results in a change in catalytic activity of the catalyst. The choice of the term analyte or trigger may depend upon context or be used interchangeably. For example, the term trigger may be used when the chemical substance is used to control the activity of the system and the term analyte may be used when it is desirable to identify the presence or amount of the chemical substance. Examples of analytes or triggers include, but are not limited to, ions, small molecules, proteins, and nucleic acids (e.g., single stranded DNA, RNA, aptamers, peptide nucleic acids, etc.). In some arrangements, the analyte or trigger is a template nucleic acid strand or a nucleic acid strand that anneals to the nucleic acid-scaffolded catalyst. Other examples of analytes or triggers for switchable scaffolded catalysts include metal ions, glucose (including the D-glucose enantiomer), hydrocortisone, and complementary DNA.
In some embodiments, the conformation in the nucleic acid-scaffolded catalyst may be induced by an analyte or a trigger, as explained above, or it may be reversed by an “anti-trigger”. In some embodiments the anti-trigger turns off the catalytic activity while in other embodiments the anti-trigger turns on the catalytic activity.
“Synergistic catalysis” as used herein refers to the combination of two catalytic components (or co-catalysts) to drive reactions that do not occur with either component alone.
In some embodiments, the switchable DNA catalysts of the present disclosure can use, but are not limited to, increasing the distance between a photocatalyst and a spectral quencher, bringing a photocatalyst close to a FRET donor, bringing two synergistic co-catalysts (such as a copper co-catalyst and a nitroxyl radical co-catalyst for synergistic alcohol oxidation) close together, and altering the coordination environment of a transition metal, for catalytic switching.
In some embodiments, the switchable DNA catalysts of the present disclosure can be used in a number of different biological or chemical processes. For example, but not limited thereto, the switchable catalysts may be used for unmasking a prodrug for therapeutics, for transcriptional control of immune chell therapies, for diagnostics, for proximity labeling for prteomic mapping and for switchable polymerization (e.g., for self-healing materials).
Referring now to the drawings, and with specific reference to
Upon addition of an analyte 18 or other stimuli, a conformational change in the nucleic acid strand 12 is triggered which changes the distance between the first reactive moiety 14 and the second moiety 16, thereby triggering a change (increase or decrease) in catalytic activity of the catalyst 11. For instance, as shown in
In another embodiment shown in
In yet another embodiment shown in
Another embodiment of a switchable catalytic system 10 is shown in
Another embodiment of the switchable catalytic system 10 is shown in
In an embodiment of the switchable catalytic system 10 shown in
In one embodiment, the catalyst includes the first nucleic acid strand which adopts a hairpin or stem-loop conformation. The first reactive moiety is a photocatalyst and the second moiety 16 is a FRET quencher (“Q”) of the photocatalyst. The photocatalyst and the FRET quencher are tethered to respective 5′ and 3′ ends (or 3′ and 5′ ends) of the nucleic acid strand. In this example, the photocatalyst may be a ruthenium complex in which a Ru′ ion is coordinated to two bipyridine ligands and one phenanthroline ligand, and the FRET quencher may be Black Hole Quencher 2 (BHQ-2). In some embodiments, the photocatalyst and the FRET quencher may be pre-installed as abiotic groups on a custom commercial nucleic acids oligomer. Upon absorption of light of an appropriate wavelength (˜450 nm), the ruthenium complex may be excited to a higher energy excited state and is capable of donating an electron or accepting an electron from a substrate, leading to conversion of the substrate to a new molecule. When in proximity to the FRET quencher in the hairpin conformation, the excited state of the ruthenium complex is quenched and catalytic activity is suppressed. In the presence of an analyte that binds to the nucleic acid strand, a conformation change is triggered that opens the hairpin and moves the ruthenium complex far from the FRET quencher and activates catalytic activity.
The catalytically active (“on”) and catalytically inactive (“off”) states of the any of the systems described herein having a photocatalyst and a FRET donor or quencher (e.g.,
An exemplary synthetic scheme for the preparation of the ruthenium complex photocatalyst, and conjugation of the ruthenium complex to DNA is shown in synthetic schemes 8, 9, and 10 in Example 2 below. 1,10-phenanthrolin-5-amine reacted with 4-pentynoic acid in the presence of 4-dimethylaminopyridine (DMAP) and 1-ethyl-3-(3′-dimethylaminopropyl)carbodiimide hydrochloric acid (EDC-HCl). The alkynylated product may be coordinated with cis-dichlorobis(bipyridine)ruthenium (II) (Ru(bpy)2Cl2), and then conjugated to an azide-functionalized DNA strand via click chemistry.
Referring to
In some embodiments, polymerization of 3,-3′-diaminobenzidine (DAB) may be controlled via a switchable nucleic acid-scaffolded catalytic system of the present disclosure. Polymerization of DAB is a reaction that is useful for generating localized contrast for electron microscopy of biological samples. One exemplary switchable nucleic acid-scaffolded catalytic system 10 for this purpose is shown in
In another arrangement shown in
Radical polymerization of the poly(ethylene glycol) diacrylate (PEGDA) monomer was also demonstrated in the triggered catalyst 11 of
Other possible pairs of reactive moieties for catalytic systems of the present disclosure are shown in
Another embodiment of the nucleic acid-scaffolded synergistic catalytic system 10 is shown in
In one example, a nucleic acid-scaffolded synergistic catalytic system 10 for alcohol oxidation is shown in
As demonstrated in Example 1, and referring to
The above oxidation rate acceleration was not specific to 2-napthalenemethanol; it also was observed for six other benzyl alcohol derivatives (see
To further confirm that the nucleic acid-scaffolded synergistic catalytic system 10 operates through an intramolecular reaction mechanism (i.e., copper and TEMPO interact on the same DNA helix), the TONs for scaffolded (DNA duplex scaffold formed with SEQ ID NO: 5 and SEQ ID NO: 6) and unscaffolded 2-napthalenemethanol oxidation reactions at different catalyst loadings were compared (see
The increase in effective concentration of the TEMPO radical and bpy-Cu catalyst provided by the scaffolded system was estimated experimentally. Initial rates of alcohol oxidation by a single catalyst tethered to DNA in the presence of non-tethered co-catalyst were measured, reasoning that a sufficiently high concentration of non-tethered co-catalyst could mimic the high local concentration of the DNA-tethered co-catalyst. It was found that 50 micromolar (□M) of the nucleic acid-scaffolded Cu-TEMPO catalyst exhibited a reaction rate equivalent to that expected for 34 mM of the non-tethered TEMPO catalyst (
A key advantage of DNA as a scaffold for synergistic catalysis is the ability to control the relative spacing of the catalysts using templating strands which facilitate modular assembly of 2D and 3D architectures. As demonstrated in the Examples, this advantage for Cu-TEMPO synergistic catalysis was explored by annealing DNA-catalyst conjugates (SEQ ID NO: 8 and SEQ ID NO: 6) to a series of unmodified templating strands with varying single-stranded spacers controlling the inter-catalyst distance (
Another embodiment of the switchable nucleic-acid scaffolded synergistic catalytic system 10 is shown in
In another aspect, a change in catalytic activity of the catalytic system 10 is dependent on the presence of two cell surface antigens. In such a system depicted in
A demonstration of proximity-driven activation of a nucleic acid-scaffolded system on the surface of living yeast cells is shown in
In another aspect, the disclosure the switchable nucleic acid-scaffolded catalyst of the present disclosure may be used for studying and targeting cancer cell—immune cell contacts, based on the use of switchable proximity labeling catalysts that activate only at contact sites of interest. Specific protein-protein interactions at contact sites between cancer cells and immune cells, as well as contacts between different types of immune cells (e.g. the immunological synapse), mediate cancer immune response and evasion. For example, the interaction between programmed death receptor 1 (PD-1) and its ligand (PD-L1) is implicated in suppression of T cell activity and acceleration of tumor progression. 4 In another example, a variety of protein-protein interactions at contact sites between NK cells and cancer influence whether the NK cells are activated or inhibited in their immune response. The switchable catalyst described herein can be used to study and understand the mechanisms of cancer immune cell evasionby determining proteins mediating the evasion process. To develop such a “proteomic list,” one promising approach is to use proximity labeling catalysts for spatially restricted proteomic mapping. In these methods, a catalyst—such as a peroxidase (APEX or HRP) or a photocatalyst—is tethered to a synaptic protein of interest, and a small molecule probe, consisting of a substrate for the catalyst tethered to biotin, is introduced. The catalyst converts the substrate into a reactive species that bonds covalently with nearby proteins, but only within a tight labeling radius, owing to rapid quenching of the reactive species. Nearby proteins are thus tagged with biotin, which is followed by lysis, pull-down using streptavidin, and identification of the proteome using high-resolution mass spectrometry. Despite the promise of proximity labeling approaches, the specificity of labeling at cell-cell contacts is intrinsically limited because the protein to which the catalyst is appended may not be localized exclusively at the contact sites in the methods used in the art (
The switchable catalyst of the present invention are able to overcome the shortcomings of the prior art by being “smart” proximity labeling catalysts that activate selectively at cell-cell contacts (
The switchable catalysts can be used in both in vitro proximity labeling of purified proteins (e.g., biotin tagging using imaging and Western blot assays) and targeting the DNA nanocatalysts to the surface of cancer cell lines through attachment to a genetically encoded recombinant protein. Activity of the nanocatalysts for spatially-restricted biotin tagging will de determined and verified that catalyst activation is dependent on the presence of the “trigger” protein. For example, mixed cell culture assays, can be used in which one cell line will be coated with the DNA nanocatalyst, and the other will be coated with the “trigger” protein that activates the nanocatalyst. The proximity biotin labeling substrate will be added into this mixed culture, performing the photocatalytic reaction, and images can be gathered as to whether biotin tagging occurs exclusively at the intended cell-cell contact sites.
In some aspects, the switchable nucleic acid-scaffolded catalysts may be used for proximity labeling at extracellular PPIs, whereby catalyst activation triggered by the conformational change leads to conversion of a substrate into a reactive intermediate which promiscuously tags endogenous proteins within a defined labeling radius. Using nucleic acid-scaffolded catalysts for this purpose includes advantages such as the ability to fine-tune the nucleic acid constructs to ensure sensitive reconstitution while avoiding perturbation of the PPIs, and the availability of multiple synthetic photocatalysts and proximity labeling chemistries that can be used in the platform.
An exemplary application of the switchable nucleic acid-scaffolded catalysts for proximity labeling at intercellular PPIs is shown in
In another aspect of proximity labeling using the switchable catalysts, a split invader system may be used. Split invader systems include two “split invader” oligos, with each split invader oligo attached to a DNA aptamer to recruit a specific epitope. A “full invader” may form when two split invaders bind in immediate proximity on a surface (i.e., a cell, a bead, a plastic substrate, a glass substrate, a metallic substrate, a paper substrate, a composite substrate, a ceramic substrate) and anneal to each other. For this activation mechanism, a photocatalyst ssDNA strand and a quencher ssDNA strand may be annealed in a duplex. In the duplex conformation, the photocatalyst is inactive due to its proximity to the quencher. In some embodiments the split invader oligos are attached to an aptamer, antibody, antigen, or protein-protein interactions given in Table 2. In some embodiments the split invader targets interact in a protein-protein interaction. In other embodiments, the split invader targets do interact in a protein-protein interaction.
Additionally, the switchable nucleic acid-scaffolded catalysts of the present disclosure may be used for detection and/or isolation of circulating tumor cells (CTCs) that have detached from the primary tumor (for example, see
In another aspect, the technology disclosed herein may be included in a kit intended for performing an assay. In some embodiments the assay may perform proximity labeling with previously discussed split invader systems. In some embodiments the assay perform proximity labeling on eukaryotic cells, including mammalian and non-mammalian cells. In other embodiments, the assay may perform proximity labeling on prokaryotic cells.
The assay kit contains all necessary reagents and standards for calibrating said one or more assays and for performing said one or more assays on one or more unknown samples. In one embodiment, the assay may contain at least one photocatalyst ssDNA strand and at least one quencher ssDNA strand annealed in a duplex, at least two split invader oligos with each split invader attached to a target (i.e., an aptamer or antibody) corresponding to at least two suspected antigens or epitopes found in the user-supplied sample. Examples of targets are explored in Example 2 and Table 2.
In some embodiments the assay is a mix-and-read assay (i.e., a homogenous, non-separation assay). In some embodiments the assay is read optically, spectroscopically (i.e., by fluorescence emission, by infrared emission, by ultraviolet emission, or by Raman scattering), or colorimetrically. In some embodiments, the assay may be used for proximity labeling of endogenous proteins within a defined radius of the site of catalyst activation, and the assay kit components may include a proximity labeling substrate such as biotin phenol and the oxidant ammonium persulfate. In some embodiments, the assay may be used for synthesis of cross-linked polymer hydrogels at the site of catalyst activation, and the assay components may include poly(ethylene glycol) diacrylate, triethanol amine, and N-vinylpyrrolidone.
It should be apparent to those skilled in the art that many additional modifications beside those already described are possible without departing from the inventive concepts. In interpreting this disclosure, all terms should be interpreted in the broadest possible manner consistent with the context. Variations of the term “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, so the referenced elements, components, or steps may be combined with other elements, components, or steps that are not expressly referenced. Embodiments referenced as “comprising” certain elements are also contemplated as “consisting essentially of” and “consisting of” those elements. The term “consisting essentially of” and “consisting of” should be interpreted in line with the MPEP and relevant Federal Circuit interpretation. The transitional phrase “consisting essentially of” limits the scope of a claim to the specified materials or steps “and those that do not materially affect the basic and novel characteristic(s)” of the claimed invention. “Consisting of” is a closed term that excludes any element, step or ingredient not specified in the claim. For example, with regard to sequences “consisting of” refers to the sequence listed in the SEQ ID NO. and does refer to larger sequences that may contain the SEQ ID as a portion thereof.
All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In the case of conflict, the present specification, including definitions, will control.
Other features and advantages of the invention will be apparent from the description of the preferred embodiments thereof, and from the claims. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
Creation of catalysts that mimic enzymes through the pre-organization of multiple reactive groups is a long-standing goal. In natural enzymes, protein scaffolds hold multiple functional groups in proximity, engendering massive rate accelerations that are not observed when the same functional groups are unscaffolded. While matching the sophistication of enzymes has been elusive in synthetic systems, supramolecular enzyme mimics offer a broader palette of functional groups, since they are not limited to the natural amino acids and cofactors. Impressive catalytic properties have been demonstrated in a variety of enzyme-mimicking supramolecular scaffolds.
An exciting area of recent progress in supramolecular catalysis is the pre-organization of synergistic catalytic reactions. Synergistic catalysis combines two co-catalysts to carry out a reaction that would not be possible using either co-catalyst alone. Examples include a variety of synergistic combinations of transition metal catalysts, photocatalysts, organocatalysts, radical catalysts, and Lewis acid catalysts. In scaffolded synergistic catalysis, the proximity afforded by precise positioning of the co-catalysts accelerates the reaction compared to unscaffolded reactions, in which the large mean distance between the co-catalysts limits synergistic interactions, often necessitating high loadings. Successful demonstrations of scaffolded synergistic catalysis have utilized peptoids, peptides, foldamers, soluble proteins, metal—organic frameworks, covalent—organic frameworks, and polymers. However, it remains challenging to fine-tune the spacing of each co-catalyst. Furthermore, the previously demonstrated scaffolds for synergistic catalytic reactions are difficult to engineer for stimuli-triggered conformational changes to alter the rate of the reaction. This important property of enzyme catalysis, allostery, is of fundamental interest for enzyme-mimicking systems and for the development of sensors and responsive materials.
Inventors envisioned that DNA-scaffolded synergistic catalysis would offer multiple advantages: 1) precise positioning of the catalysts due to the programmability of DNA and the ease of site-specific modification, 2) convergent and facile synthesis of many catalyst variants through one-step bioconjugation followed by self-assembly, and 3) allosteric switching using DNA strand displacements (
Inventors chose Cu/TEMPO alcohol oxidation as a proof-of-principle reaction to demonstrate DNA scaffold-dependent rate enhancement because of its remarkably mild reaction conditions and the synergistic cooperation of the two co-catalysts. Additionally, Cu/TEMPO oxidations have been accelerated through arranging the two co-catalysts on several different scaffolds, including peptoids, silica particles, and simple synthetic tethers. Inventors envisioned that a DNA scaffold could allow for similar enhancements in reactivity while also allowing highly tunable co-catalyst positioning.
Inventors prepared a simple DNA duplex with the two co-catalysts (Cu and TEMPO) attached to the end of the helix via sufficiently long tethers to span the 2 nm diameter of B-form DNA (
Catalytic activity of the scaffolded DNA duplex (0.5 mol %) was evaluated by monitoring oxidation of 2-napthalenemethanol (
Control reactions confirmed that scaffold-induced proximity of the co-catalysts was responsible for the observed activity enhancement (
To further confirm that the DNA-scaffolded synergistic co-catalysts operate through an intramolecular reaction mechanism (i.e., Cu and TEMPO interact on the same DNA helix), inventors compared the TONs of the scaffolded and unscaffolded reactions at different catalyst loadings (
To further investigate the DNA-scaffolded Cu-TEMPO activity enhancement, inventors estimated the increase in effective concentration experimentally and using a simple theoretical model. Inventors measured the initial rates of alcohol oxidation by a could potentially mimic the high local concentration of the DNA-tethered co-catalyst. Inventors determined that 5011M of the DNA-scaffolded Cu-TEMPO catalyst exhibited a reaction rate equivalent to that expected for 7 mM of the non-tethered dcbpy-Cu complex and 34 mM of the non-tethered TEMPO catalyst (
A key advantage of DNA as a scaffold for synergistic catalysis is the ability to control the relative spacing of the catalysts using templating strands, which facilitate modular assembly of 2D and 3D architectures. Inventors explored this advantage for Cu-TEMPO catalysis by annealing DNA-catalyst conjugates to a series of unmodified templating strands, with varying single-stranded spacers controlling the inter-catalyst distance (
Taking inspiration from dynamic strand interchange reactions 61 and the widespread application of FRET-based molecular beacons, inventors envisioned that proximity-dependent synergistic catalysis might be incorporated into a stimulus-responsive switch architecture (
In conclusion, inventors have successfully demonstrated the first DNA-scaffolded acceleration of synergistic catalysis, using Cu/TEMPO oxidation of alcohols as a model reaction. The DNA backbone allowed for systematic exploration of the scaffolded reactivity, and inventors' data suggest that the reactivity enhancement is due to the increased effective concentration afforded by proximity of the scaffolded co-catalysts. The DNA backbone allowed for dynamic activity switching using a strand-displacement approach. While this initial demonstration was not intended to pursue a new synthetic method, with further optimization this scaffolding approach may provide solutions to challenges in synergistic catalysis. DNA-scaffolded synergistic catalysis will be a promising strategy to accelerate other synergistic catalytic reactions (beyond Cu-TEMPO oxidation) in which interactions between the two co-catalysts are rate-limiting. This acceleration may allow for low catalyst loadings in reactions that currently require high concentrations of both co-catalysts and may even unlock new reactions that are inaccessible in an unscaffolded format. Furthermore, information-encoding properties of DNA could enable DNA-encoded discovery of synergistic catalysts. Finally, the groundwork laid in this study could be applied to create functional DNA nanomaterials containing synergistic catalytic sites.
Materials
All solvents used in this study were purchased from Sigma Aldrich in HPLC Grade and used without further purification. All reagents were purchased from TCI, Fisher, Sigma Aldrich, Santa Cruz Biotechnology, Alfa Aesar, or Ambeed and used without further purification. Unmodified and amine-modified DNA oligonucleotides were purchased from Integrated DNA Technologies with standard desalting.
HPLC Analysis and Purification
Reverse-phase HPLC analysis and purification of DNA conjugates and reverse-phase HPLC reaction tracking were performed on a Shimadzu Prominence HPLC system with quantification at 254 nm. HPLC analysis and purification of DNA oligonucleotides was performed using a 4.0×300 mm Kromasil 100-5-C18 column with 1.0 mL/min flow under ion-pairing conditions using aqueous 100 mM triethylammonium acetate pH 7.0 (TEAA) as mobile phase A and acetonitrile as mobile phase B (using a gradient from 10-30% B over 10 minutes, followed by a 1 minute ramp to 90% and a 1 minute wash at 90% B and then re-equilibration at 10% B), with a column oven temperature of 50° C. HPLC reaction tracking of alcohol oxidation was performed using a 4.6×50 mm)(Bridge C18 (3.5 μm) column with 1.0 mL/min flow using water with 0.1% trifluoroacetic acid as mobile phase A and acetonitrile as mobile phase B, with a column oven temperature of 30° C. (using a gradient from 10-90% B over 5 minutes, followed by a 1.5 minute wash at 90% B and then re-equilibration at 10% B). The differences in absorbance at 254 nm for each substrate and product were accounted for by construction of calibration curves in triplicate in the linear range of each compound.
NMR Spectroscopy
1H and 13C{1H} NMR spectra were recorded on a Bruker Avance 500 MHz spectrometer. Chemical shifts (δ) are given in parts per million and referenced to TMS.
UV-Vis Spectroscopy
DNA concentrations were determined by UV-Vis spectroscopy (absorption at 260 nm) using a Nanodrop One Spectrophotometer (ThermoFisher Scientific).
Mass Spectrometry
All MS and MS/MS experiments were performed on a quadrupole-Orbitrap-quadrupole linear ion trap (q-OT-QLT) hybrid mass spectrometer system (Orbitrap Fusion Lumos, Thermo Fisher Scientific, San Jose, CA) that was modified to perform negative electron transfer dissociation (NETD). 1 Following purification with ion-exchange HPLC, samples were diluted to 51.1M of ssDNA-catalyst conjugate in 70% acetonitrile and 30% nuclease-free water with 10 mM ammonium acetate. Solutions were pH-adjusted to pH 9.5 with ammonium hydroxide. The ssDNA-catalyst conjugate samples were directly infused at a flow rate of 3 μL/min, and anions were generated via electrospray in the negative ion mode with a heated electrospray voltage of −2.2 kV relative to ground and a transfer tube temperature of 300° C. The ion funnel RF was held at 60%. All MS survey spectra were collected at a resolving power of 500,000 at 200 m/z in the Orbitrap with a scan range of 400-3,000 m/z, an AGC target of 400,000 charges and a maximum injection time of 50 ms. To aid in desolvation, nitrogen sheath and auxiliary gas were applied at 15 and 10 arbitrary units, respectively. MS/MS experiments were briefly carried out to confirm the identity of putative adducted species. After a 30 ms NETD reaction with fluoranthene radical cations (reagent AGC target=100,000), all product ions and unreacted precursor ions were shuttled to the ion routing multipole for beam-type collisional dissociation at 25 normalized collisional energy (NEThcD) and scanned out in the Orbitrap with resolving power of 240,000 at 200 m/z. Upon fragmentation, no site-specificity was determined for adducts. All MS and MS/MS data were collected in profile mode. For increased signal-to-noise (S/N), MS spectra are the sum of 50 individual scans, with averaging performed in the vendor's post-acquisition software (XCalibur Qual Browser, version 2.2). No microscans were performed.
Gel Electrophoresis
2% agarose gels (cast with 3 μL of a 10 mg/mL aqueous stock of ethidium bromide for every 50 mL of molten gel solution, for DNA visualization) were prepared in 1×TAE buffer and run for 40 minutes at 120 V. Gel images were recorded on an Azure C400 Gel Imaging System (Azure Biosystems) using 302 nm transillumination.
Fluorescence Reaction Tracking
Fluorescence experiments were recorded on a Tecan Spark fluorescence plate reader with the following conditions: 350 nm excitation wavelength with a 5 nm bandwidth, 450 nm emission wavelength with a 10 nm emission bandwidth, 30 flashes with an integration time of 40 μs, and no delay time.
DNA Sequences
All sequences used in this paper are listed below, each named using a unique identifying code of the form dna ##. Catalyst conjugates prepared are referred to by the original sequence and the attached molecule (e.g. dna ##+dcbpy or dna ##+cTEMPO). /3AmMO/and/5AmMC6/are codes used by the DNA supplier (Integrated DNA Technologies) to refer to amino-modifications positioned at the 3′ and 5′ ends of synthetic oligonucleotides.
Sequences used in
Synthesis and Characterization
In a 1.5 mL centrifuge tube, 100 nmol of amine-modified DNA oligonucleotide (10 mM stock in nuclease-free water) was diluted with 290 μL of 250 mM sodium borate buffer, pH 9.5 and 100 μL of DMSO. 100 μL of a 0.25 M stock of 4,4′-dicarboxy-bipyridine (dcbpy, in 1:1 250 mM sodium borate buffer, pH 9.5 and DMSO, 250 equivalents), was then added, followed by 400 μL of 0.5 M DMTMM-Cl (in nuclease-free water, 2000 equivalents). The sample was vortexed thoroughly, spun down in a bench-top centrifuge, and then incubated for 16 hours at 17° C. with 500 rpm shaking in an Eppendorf thermomixer. At this point, the sample was spun down to pellet any precipitate and then concentrated by transferring the supernatant to and concentrating in a 3K Amicon Ultra-0.5 mL centrifugal filter device (prerinsed with 500 μL of nuclease-free water and spun down at 14000 rcf for 10 minutes, then loaded with sample and concentrated by spinning as before). The device was then diluted with 400 μL nuclease-free and concentrated by spinning as before, three times to remove residual ligand. The retentate was recovered and the membrane was rinsed with 50 μL nuclease-free water to maximize recovery. The concentration of crude DNA-conjugate was then checked by UV absorption at 260 nm using a NanoDrop spectrometer. The isolated conjugate was then purified by HPLC by iterative injection of 20 nmol aliquots. The product-containing fractions were then pooled, lyophilized, buffer-exchanged with nuclease-free water on a second Amicon Ultra filtration device to remove residual TEAA from the HPLC purification, and then subjected to a final lyophilization before resuspension in nuclease free water to approximately 1 mM concentration. The final concentration of conjugate was determined using a NanoDrop spectrometer. Yields ranged from 35-80 nmol of HPLC-purified DNA conjugate. To assess the integrity of oligonucleotide-catalyst conjugates, intact mass analysis via electrospray mass spectrometry (ESI-MS) was performed (see “Mass Spectrometry”).
In a 1.5 mL centrifuge tube, 100 nmol of amine-modified DNA oligonucleotide (10 mM stock in nuclease-free water) was diluted with 90 μL of 100 mM triethylammonium borate buffer, pH 8.0 and 250 μL of DMSO. To this solution was added 50 μL of an 0.5 M stock of 4-carboxy-TEMPO (cTEMPO, 250 equivalents) in DMSO, 100 μL of a 0.3 M stock of EDC-HCl in DMSO (300 equivalents), 50 μL of a 0.12 M stock of HOAt in DMSO (60 equivalents) and 50 μL of a 0.6 M stock of DIPEA in DMSO (300 equivalents). The sample was then vortexed thoroughly, spun down in a benchtop microcentrifuge, and then incubated for 16 hours at room temperature without shaking. The sample was then precipitated by isopropanol precipitation (40 μL 3 M sodium acetate, 1 mL cold isopropanol, spun down at 21000 rcf at 4° C. for 30 minutes). The supernatant was decanted, and the pellet was rinsed with two 200 μL portions of cold 70% ethanol, air-dried, and resuspended to approximately 1 mM concentration with nuclease-free water. The concentration of crude DNA was then checked by UV absorption at 260 nm using a NanoDrop spectrometer. The isolated conjugate was then purified by HPLC by iterative injection of 20 nmol aliquots. The product-containing fractions were then pooled, lyophilized, and buffer-exchanged with nuclease-free water on a second Amicon Ultra filtration device to remove residual TEAA from the HPLC purification. The sample was then subjected to a final lyophilization before resuspension in nuclease free water to approximately 1 mM concentration. The final concentration of the conjugate stock was determined using a NanoDrop spectrometer. Yields ranged from 35-50 nmol of HPLC-purified DNA conjugate. To assess the integrity of oligonucleotide-catalyst conjugates, intact mass analysis via electrospray mass spectrometry (ESI-MS) was performed (see “Mass Spectrometry”).
6-methoxy-2-naphthaldehyde (2 g, 10.7 mmol, 1 equivalent) was dissolved in 50 mL HPLC-grade methanol (no precautions were taken to dry the solvent) in a 100 mL round-bottom flask with stirring. Sodium borohydride (0.450 g, 11.9 mmol, 1.1 equivalents) was then added in 50 mg portions (vigorous bubbling was observed after each addition, and the color of the reaction mixture changed from clear orange to a yellow-green). 2 mL of methanol were used to rinse residual sodium borohydride from the edges of the flask into the mixture, the reaction was placed under a nitrogen atmosphere and stirred at room temperature until complete consumption of the aldehyde was observed by TLC (5% ethyl acetate in hexanes, with visualization by UV and KMnO4 staining). The solvent was then removed under reduced pressure and resulting off-white solid was redissolved in 50 mL of ethyl acetate. The organic layer was then partitioned with 20 mL of a saturated aqueous solution of ammonium chloride and 20 mL of distilled water. The aqueous layer was extracted with 3×20 mL ethyl acetate, and all organic layers were combined. The organic layers were then washed with 10 mL distilled water followed by 10 mL brine. The combined organic layers were dried over anhydrous magnesium sulfate, filtered and the solvent was removed under reduced pressure. This yielded 1.80 g (89.6% yield) of product as a beige powder. The structure was confirmed by 1H- and 13C-NMR. 1H-NMR (500 MHz, CDCl3) δ 7.76-7.70 (m, 3H), 7.45 (dd, J=8.5, 1.7 Hz, 1H), 7.18-7.11 (m, 2H), 4.82 (s, 2H), 3.92 (s, 3H), 1.72 (s, 1H). 13C NMR (126 MHz, CDCl3) δ 157.76, 136.06, 134.14, 129.37, 128.82, 127.22, 125.88, 125.59, 119.02, 105.76, 77.27, 77.02, 76.77, 65.59, 55.31.
1/3AmMO/ and /5AmMC6/ are codes used by the DNA supplier
Protein-protein interactions (PPIs) and multi-protein complexes are essential for intercellular communication and for transmitting extracellular signals across the plasma membrane. Therefore, methods that determine which proteins are proximal to a specific extracellular protein of interest (POI) are important for studying cellular signaling. Traditionally, methods such as co-immunoprecipitation or photo-cross-linking have been used to determine which proteins interact with a POI. However, these methods require a direct interaction with the protein of interest, which in some cases is advantageous, but which precludes the discovery of proteins that are close to the POI without directly contacting it. Recently, an approach called proximity labeling (PL) has been developed to identify endogenous proteins within a defined radius of a POI, even if those proteins do not directly contact the POI. In PL methodologies, the POI is attached to a catalyst, which generates a reactive species that covalently tags endogenous proteins within a restricted radius, determined by the lifetime of the reactive species. Next, cells are lysed, the tagged proteins are isolated using affinity purification, and the enriched proteins are identified using mass spectrometry. Alternatively, the PL catalyst can be attached to another a non-proteinaceous biomolecule of interest or targeted to a cellular organelle.
A variety of PL catalysts have been reported, along with multiple approaches for attaching the catalyst to a POI. Some PL methods involve the attachment of an enzyme, such as the biotin ligases BioID or TurboID or a heme peroxidase, to the POI through genetic fusion or antibody targeting. In the case of biotin ligases, the enzyme converts endogenous biotin to an adenylate ester, which reacts with nucleophilic residues on proximal endogenous proteins. Heme peroxidases, such as horseradish peroxidase (HRP) and enhanced ascorbate peroxidase 2 (APEX2), catalyze the H2O2-dependent oxidation of biotin phenol into a phenoxy radical, which forms covalent adducts primarily with surface-exposed tyrosine residues.
As an alternative to enzymes, a variety of synthetic photocatalysts have recently been developed for PL. These photocatalysts are targeted to the POI using an antibody or other binding moiety, which is advantageous for use in untransfected cells, and the requirement for photo-irradiation allows for precise control over reaction time. Furthermore, several synthetic photocatalysts have expanded the scope of PL labeling mechanisms beyond those accessible with genetically encodable enzyme catalysts. Ruthenium, iridium, or flavin catalysts have been used for the oxidative coupling of phenols, anilines, or urazoles onto tyrosine or tryptophan residues of endogenous proteins. In a mechanistically distinct approach, photosensitizers such as dibromo-fluorescein, thiorhodamine, and BODIPY were used to generate singlet oxygen in the presence of nucleophilic probes, leading to covalent modification of histidine residues. A genetically encoded photosensitizer (miniSOG) was recently reported to catalyze intracellular PL by the same mechanism. An iridium photocatalyst or a variety of organic dyes were used to convert aryl azides into electrophilic moieties that labeled nucleophilic protein residues, while a SnIV chlorin e6 photocatalyst or osmium photocatalyst was used to convert aryl azides to aminyl radicals or triplet nitrenes. Using an iridium photocatalyst, it was shown that a diazirine could be converted to a carbene with a 2-nanosecond lifetime, which is advantageous for achieving a short labeling radius.
While PL methods have been transformative in elucidating proteomes proximal to a POI, new PL methods are needed for determining proteomes in subcellular regions that cannot be defined by the location of a single POI (
Here, inventors report DNA-based switchable PL catalysts that can be attached to a POI and become active only when a secondary molecular trigger is present (
As an initial photocatalyst to demonstrate DNA-based switchable PL catalysis, inventors selected a heteroleptic Ru(bpy)2(phenanthroline) complex for oxidation of the small molecule biotin phenol (BP) because Ru(bpy)3-type complexes are well-established for oxidative phenol couplings on proteins. Ru(bpy)3 has also been shown to catalyze the oxidative coupling of two BP molecules in the presence of ammonium persulfate (APS), as well as the oxidative coupling of BP to tyrosine residues. Additionally, these complexes have a catalytically active photoexcited state that can be quenched through proximity to a spectral quencher, and they are DNA compatible.
Inventors synthesized the switchable DNA catalyst by appending abiotic groups onto individual single-stranded DNA (ssDNA) strands, then annealing the strands together (
Inventors assembled the switchable DNA PL catalyst by combining the quencher and Ru ssDNA oligos with a slight (1.4 eq) excess of quencher DNA to ensure full quenching.
Next, inventors investigated whether the DNA catalyst exhibited PL activity that could be triggered by the presence of a ssDNA trigger oligo, which is complementary to the loop region of the hairpin sequence. Inventors first used Ru luminescence to assess whether the Ru complex was quenched in the “off” conformation and whether luminescence could be activated in the “on” state. Inventors observed a 19-fold increase in luminescence upon addition of the trigger strand.
Inventors next investigated the ability of the switchable DNA PL catalyst to label proteins in vitro. Inventors combined the DNA catalyst with a purified protein (bovine serum albumin, BSA), in the presence or absence of its DNA trigger, along with BP and the oxidant ammonium persulfate (APS). Inventors included APS as a terminal oxidant, following the precedent that APS can oxide the excited state *Ru(II) com-plex to a Ru(III) complex which can oxidize BP to afford the phenoxy radical and ground state Ru(II) complex. The DNA catalyst was not bound to BSA in this experiment, but the DNA catalyst and BSA were added at high concentrations such that BSA could be tagged by biotin phenoxy radicals generated by the catalyst. Photocatalytic BP oxidation was initiated by irradiation with blue light (450 nm), and Western blotting was used to detect covalent biotin modifications of BSA. In its “off” state, the DNA catalyst exhibited similar protein labeling to negative controls in which BP was omitted (
Next, inventors tested whether the switchable DNA catalyst could become activated on streptavidin-coated magnetic beads. To target the DNA catalyst to streptavidin on the beads, inventors attached a ssDNA overhang and annealed it to a complementary biotinylated ssDNA oligo (
After observing DNA catalyst activation with a ssDNA trigger, inventors next explored proximity driven activation using a split invader system, toward the goal of activating PL at the sites of PPIs. For this activation mechanism, a photocatalyst ssDNA strand and a quencher ssDNA strand are annealed in a duplex. In the duplex conformation, the photocatalyst is inactive due to its proximity to the quencher. Two “split invader” oligos are introduced, with each split invader being attached to a DNA aptamer that recruits it to a specific epitope. If the two split invaders bind in immediate proximity on the surface of a bead or a living cell, they anneal to each other to form a “full invader” that anneals to the photocatalyst-containing duplex and displaces the quencher strand, thus activating PL. Importantly, both split invader oligos are necessary to activate PL catalysis.
For initial validation of the split invader system, inventors used thrombin coated beads and appended the split invaders to two thrombin aptamers, HD1 and HD22, which bind to distinct sites on thrombin. Each aptamer sequence was extended to contain a short ssDNA sequence (C or C*) complementary to the other DNA construct (
Inventors applied the split invader approach to activate PL at the sites of PPIs on living mammalian cells. Inventors selected homodimerization of c-Met, a receptor tyrosine kinase that is expressed on epithelial cells, as the target PPI. While C-Met plays a crucial role in several biological processes such as wound healing, dysregulation of the receptor or its natural ligand, hepatocyte growth factor (HGF), can lead to invasive growth of aggressive tumors. To activate PL selectively at c-Met homodimers, inventors employed a split invader approach that was previously used for fluorescence detection of c-Met homodimerization. In this design, each split invader construct consists of the c-Met aptamer elongated on either the 5′ or 3′ end with a poly-T linker, an 8-nucleotide complementary region (C or C*), and one of the split invader sequences (A or B) (
Inventors transfected HEK293T cells with a plasmid encoding C-Met, along with a plasmid encoding blue fluorescent protein localized to the nucleus (BFP-NLS) as a co-transfection marker. Inventors treated the transfected cells with the split invader oligos and the photocatalyst-quencher duplex. After oligo labeling, cells were photoirradiated in the presence of BP, then stained with sAv-PE. By epi-fluorescence microscopy, inventors observed strong PE signal on the perimeter of transfected cells when both intact split invader-aptamers were added (Apt-CA+Apt-C*B), as shown in
Inventors have developed a new approach for activation of PL photocatalysis in highly specific subcellular locations. The approach offers multiple advantages. First, it takes advantage of the established ability of DNA conformational changes to alter the distance between a chromophore and a spectral quencher, as in molecular beacon probes. DNA oligomers have been reported to bind a wide array of chemical stimuli including small molecules, ions, and proteins. Thus, switchable DNA PL catalysts can in principle be tailored to respond to any of these stimuli. Furthermore, split invader DNA strands allow for activation of PL at PPIs, as inventors demonstrate in this study. Because this method uses a photocatalyst, PL is controlled by light, which means that labeling is dependent on three conditions: 1) the presence of the DNA catalyst, 2) the presence of the molecular trigger, and 3) photo-irradiation. The switchable DNA PL catalyst platform is compatible with any photocatalyst for which a suitable spectral quencher exists, thus expanding the possible catalyst and substrate combinations to the large toolkit of photoredox chemistry.
All solvents used in this study were purchased from Sigma Aldrich in HPLC Grade and used without further purification. All DNA oligos were purchased from Integrated DNA Technologies with standard desalting or HPLC purification if required. Vendors for chemicals are listed within the specific procedures. Plasmid for c-Met (HG10692-CF) was purchased from Sino Biological. Nuclear-localized BFP was a previously reported plasmid, LAP-BFP-NLS.1 HPLC analysis and purification of DNA conjugates
Reverse-phase HPLC analysis and purification of DNA conjugates were performed on a Shimadzu Prominence HPLC system with analysis at 254 nm unless stated otherwise. HPLC analysis and purification were performed using a 4.0×300 mm Kromasil 100-5-C18 column with a 1.0 mL/min flow under ion-pairing conditions using aqueous 100 mM triethylammonium acetate pH 7.0 (TEAA) as mobile phase A and acetonitrile as mobile phase B (using a gradient from 10-20% B over 10.5 minutes, followed by a half-minute ramp to 80% and a half-minute wash at 80% B and then re-equilibration at 10% B), with a column oven temperature of 50° C.
1H and 13C{1H} NMR spectra were recorded on a Bruker Avance 500 MHz spectrometer. Chemical shifts (δ) are given in parts per million and referenced to TMS (if CDCl3 was used as the solvent).
DNA concentrations were determined by UV-Vis spectroscopy (absorption at 260 nm and/or 450 nm) using a Nanodrop One Spectrophotometer (ThermoFisher Scientific).
ESI-MS Small molecule high resolution mass spectrometry spectra were obtained on a Thermo Q Exactive™ Plus by the mass spectrometry facility at the University of Wisconsin-Madison. The purchase of the Thermo Q Exactive™ Plus in 2015 was funded by NIH Award 1S10 OD020022-1 to the Department of Chemistry. ESI-MS of Ru-functionalized DNA oligos were obtained on a Thermo Q Exactive™ Focus within the mass spectrometry facility at the University of Wisconsin-Madison
Luminescence Measurements were recorded on a Tecan Spark fluorescence plate reader with the following conditions: 450 nm excitation wavelength with a 10 nm bandwidth, 620 nm emission wavelength with a 10 nm emission bandwidth, 30 flashes with an integration time of 40 μs, and no delay time.
Imaging was performed with an Eclipse Ts2 Inverted Routine Microscope with a 20× objective. PE (550/50 nm LED excitation, 630/75 nm emission), BFP (390/38 nm excitation, 475/90 nm emission), and differential interference contrast (DIC) images were collected using a Panda USB3.1 sCMOS Camera (PCO). Images were analyzed using NIS-Elements L and fluorophore channels in each experiment were normalized to the same intensity ranges. Acquisition times ranged from 100 ms (BFP) to 3 s (PE).
In a 600 μL PCR tube, a 22.5 μL solution was prepared consisting of 1 μM Ru-DNA, 1.4 μM Quencher DNA, and 2.6 μM Trigger DNA in phosphate buffered saline with Mg 2+(PBS-Mg: 137 mM NaCl, 2.7 mM KCl, 10 mM Na2HPO4, 1.8 mM KH2PO4, 10 mM MgCl2). The solution was incubated at room temperature for 30 minutes to allow DNA to hybridize. A 2× master mix labeling solution was then made containing 80 μM Bovine Serum Albumin (BSA, MP Biomedicals), 200 μM Biotin Phenol (Sigma), and 2 mM ammonium persulfate (VWR) in 10 mM 2-(N-morpholino)ethanesulfonic acid (MES, Fisher Scientific) buffer, pH 7.4, supplemented with 10 mM MgCl2. After the DNA incubation period, 22.5 μL of master mix was added to samples. The samples were then vortexed and briefly centrifuged. Samples were illuminated on their side while shaking with light set to 50% intensity for 5 minutes. Samples were quenched with 2 μL of 210 mM dithiothreitol (DTT, Goldbio) and allowed to sit for 5 minutes. For western blot analysis, 1.5 μL of crude sample was combined with 3.5 μL of PBS buffer, pH 7.4 and 2 μL of SDS loading dye (0.25 M Tris, pH 6.8, 10% w/v SDS, 30% v/v glycerol, 10 uM DTT, 450 uM bromophenol blue). Samples were then denatured at 95° C. for 10 minutes. The samples were loaded onto an 8% Bolt Bis-Tris SDS page gel (ThermoFisher) and run at 200 V for 8 minutes with MES-SDS running buffer (50 mM MES, 50 mM Tris Base, 0.1% SDS, 1 mM EDTA, pH 7.3). Protein was transferred to a nitrocellulose membrane for 1 hour at 10 V. Total protein was visualized by Ponceau S staining ((0.1% w/v Ponceau S (EMD Millipore) in 5% acetic acid/water, 5 minutes) followed by successive rinses with DI water to reveal protein bands. The membrane was soaked in water until the bands disappeared, and the membrane was then blocked with 3% BSA in 1.2×TBS-T (Tris Buffered Saline with Tween-20 (DOT Scientific), pH 7.5 containing 24 mM Tris, 300 mM NaCl, v/v) overnight. The membrane was then stained with 1:5000 SA-HRP (ThermoFisher) in 1% BSA, 1.2×TBS-T for 15 minutes. The membrane was washed 4×3 minutes with 1.2×TBS-T. The membrane was treated with a solution containing equal volumes of Radiance Q substrate (Azure Biosystems) and Radiance Peroxide (Azure Biosystems) then immediately visualized with an Azure C400 Gel Imaging System (Azure Biosystems) using the Chemi setting.
In a 0.6 mL PCR tube, DNA (either unmodified, Ru-modified) and Ru-alkyne were combined to a final concentration of 2 μM in PBS with 10 mM each KCl and MgCl2. Then, an equal volume of labeling solution containing 200 μM BP (or no BP) and 2 mM ammonium persulfate (APS) in 10 mM MES buffer (pH 7.4 with 10 mM MgCl2) was added. Samples were briefly centrifuged in a tabletop centrifuge. The tubes were either kept in the dark or irradiated for minutes with the photoreactor at 50% power, while laying on their sides with lids closed. After irradiation, 2 μL of 210 mM DTT was added to quench the reaction. Biotin-DNA was purchased from IDT with a single biotin modification per DNA molecule and was not subjected to the photocatalytic reaction conditions, but it was subjected to the same workup procedures as the other samples. Amicon Ultra 3K MWCO filter devices were used to remove excess BP and buffer exchanged into PBS. Three 1 μL dots were spotted in triplicate on a nitrocellulose membrane. DNA was crosslinked to the nitrocellulose membrane by UV illumination for 5 minutes. The nitrocellulose membrane was then blocked for 30 minutes with 2% BSA in 1.2×TBS-T (Tris Buffered Saline with Tween-20, pH 7.5 containing 24 mM Tris, 300 mM NaCl, 0.6% v/v) followed by staining with 1:2000 SA-HRP in 1% BSA in TBS-T for 1 hour. The membrane was washed 4×3 minutes with 1.2×TBS-T. Biotin was visualized as above. Using FIJI image analyzer, each sample's row was converted to a curve corresponding to the intensity of the three dots in each lane, with each dot producing one peak in the curve. For one row, all three peaks were integrated under the curve to quantify the luminescence produced by each of the three dots. The average intensity was calculated for each of the three replicates.
For each sample, 2 μL of Dynabeads™ M-270 Streptavidin coated beads (ThermoFisher) were placed into 1.5 mL centrifuge tubes, then washed twice with 50 μL binding buffer (50 mM Tris, pH 7.4, 300 mM NaCl, 20 mM KCl, 10 mM MgCl2, 1 mM EDTA, 0.01% tween) containing 1% BSA, using a magnetic rack to separate the magnetic beads during washes. 20 μL of probe solution, containing 1 μM of each DNA oligo, was then added to the beads, briefly vortexed and centrifuged, then incubated on their sides using a vortex with adapter head for 30 minutes at room temperature. Two washes were then performed with 50 μL of wash buffer (50 mM Tris, pH 7.4, 300 mM NaCl, 20 mM KCl, 10 mM MgCl2). Next, 20 μL of 20 μM trigger DNA oligo in wash buffer was added or wash buffer containing no DNA. After a brief vortex and centrifuge, the samples were incubated using vortex again for 30 minutes at room temperature. Samples were then washed one time with 50 μL MES binding buffer (10 mM MES, pH 7.4 with 0.5 mM EDTA, 100 mM NaCl, 20 mM KCl, 10 mM MgCl2). Beads were then suspended in 100 μL cold BP labeling solution (100 μM BP, 1 mM APS, MES binding buffer, 10% DMSO), briefly vortexed and centrifuged then exposed to irradiation for 5 minutes while on ice on a vortex head, using the photoreactor as described above and shown in Irradiation Setup. After irradiation, samples were washed two times with 50 μL wash buffer, then incubated with 1:100 sAv-PE in binding buffer containing 0.1% BSA for 40 minutes at room temperature on vortex head. Samples were then washed two times with 50 μL of wash buffer. For flow cytometry analysis, samples were diluted to a total volume of 500 μL of wash buffer, and data was collected on a Fisher Attune analysis cytometer. Samples from tubes were processed at 100 μL/min flow rate, 20,000 gated events per sample (see Figure S9 for gating only single beads), using a 561 nm laser with 577 long pass filter for excitation and a 585/16 emission filter.
Human α-Thrombin was covalently linked to Invitrogen Dynabeads MyOne Carboxylic Acid beads according to the manufacturer's instructions. Briefly, 50 μL, (0.5 mg) of bead suspension was washed two times with 50 μL, 10 mM MES buffer, pH 6. Beads were then incubated with 200 μL, of chilled 10 mg/mL EDC solution in MES buffer for 30 minutes on ice, while shaking on a vortex head. EDC solution was removed, beads were washed one time with 50 μL, MES buffer, then suspended in 25 μg of thrombin in 200 μL, MES buffer. Protein solution and beads were incubated for 3 hours on ice while shaking on a vortex head. Protein labeling solution was removed, and beads were washed three times with 1 mL PBS supplemented with 0.1% Tween-for 10 minutes at room temperature shaking on a vortex head. Beads were stored at 4° C. at a concentration of 5 mg/mL in 100 μL PBS supplemented with 0.1% Tween-20 and 0.1% BSA for up to one month.
For split invader labeling, each sample contained 2 μL (10 μg) of thrombin-coated magnetic bead suspension. Beads were washed twice with 50 μL binding buffer (50 mM Tris, pH 7.4, 300 mM NaCl, 20 mM KCl, 10 mM MgCl2, 1 mM EDTA, 0.01% tween) supplemented with (w/v) BSA. Labeling solutions were prepared containing 1 μM split invader DNA, 1 μM Ru-DNA, 1.5 μM Quencher DNA (Ru-DNA and Quencher DNA were pre-annealed at final concentration of 5 μM prior to addition to labeling solution) in 20 μL of binding buffer. After initial washes, beads were incubated with labeling solutions for 30 minutes at room temperature while shaking on a vortex head. One 50 μL wash was performed using binding buffer, and one 50 μL wash was performed using labeling buffer (10 mM MES, pH 7.4, 1 mM EDTA, 300 mM NaCl, 20 mM KCl, 10 mM MgCl2). BP labeling solution was prepared with 100 μM BP, 1 mM APS, 10% DMSO in labeling buffer. Beads were suspended in 100 μL BP labeling solution, briefly vortexed and centrifuged, then exposed to irradiation for 5 minutes while on ice on a shaking vortex head, using the photoreactor as described above and shown in Irradiation Setup. After irradiation, samples were washed two times with 50 μL binding buffer, then incubated with 1:100 sAv-PE in binding buffer containing 0.1% BSA for 40 minutes at room temperature on vortex head. Samples were then washed two times with 50 μL of wash buffer. For flow cytometry analysis, samples were diluted to a total volume of 500 μL of wash buffer, and data was collected on a Fisher Attune analysis cytometer; 100,000 gated events per sample, using a 561 nm laser with 577 long pass filter for excitation and a 585/16 emission filter. Events shown in the histograms and used for calculations in bar graphs were gated for single beads (excluding multiple beads bound together); see S9 for gating strategy.
HEK 293T cells from ATCC (CRL-3216) were cultured as a monolayer in DMEM (ATCC) supplemented with 10% (v/v) FBS (Corning) and 2 mM L-glutamine (ATCC) at 37° C. under 5% CO2. For fluorescence imaging experiments, cells were grown in TC-treated 48-well plates (Greiner Bio-One). Plates were pre-treated with 13 μg/mL human fibronectin (Sigma) for one hour at room temperature to improve cell adherence. Plates were washed once with Dulbecco's phosphate-buffered saline (DPBS, Sigma), pH 7.4 with MgCl2 and CaCl2 prior to plating cells. Cells were transfected at 30-50% confluence with 1.3 μL Lipofectamine2000 (Invitrogen) using 500 ng c-Met plasmid (HG10692-CF) and 100 ng BFP-NLS plasmid per well in serum-free media for 2 hours, after which the media containing Lipofectamine was replaced with fresh serum-containing media. The cells were then placed back in the 37° C., 5% CO2 incubator for 12-18 hours before cell labeling.
BFP and c-Met transfected cells were removed from the incubator 12-18 hours after transfection and allowed to equilibrate to room temperature. Cells were washed once with DPBS at room temperature. 200 μL of non-conjugated primary antibody (MABS1916, Sigma. 1:500 in 1% BSA-DPBS) solution was added to each well of a 48-well plate. Antibodies were incubated with cells on ice for 20 minutes followed by two washes with ice-cold DPBS. 200 μL of secondary antibody (A11004, Life Technologies. 1:500, in 1% BSA-DPBS) was then added. Secondary labeling solutions were incubated with cells on ice for 20 minutes followed by two washes with ice-cold DPBS, after which the cells were imaged.
DNA probes for live cell labeling were prepared by combining equimolar split invaders with Ru-Duplex (1:1.5 Ru-DNA: RQ-DNA) at a final concentration of 300 nM split invaders and Ru-DNA in 0.1 mg/mL Herring Sperm DNA (Sigma) DPBS supplemented with 10 mM MgCl2.
After transfection (12-18 hours) media was replaced with 100 ng/mL Hepatocyte Growth Factor (HGF, PeproTech) in serum containing media. After 30 minutes in the incubator, cells were removed and allowed to equilibrate to room temperature. Cells were washed once with DPBS at room temperature. 150 μL of DNA probe solution was added to each well of a 48-well plate. Probes were incubated with cells at room temperature for 45 minutes followed by two washes with DPBS supplemented with 10 mM MgCl2, the first wash at room temperature, the second on ice.
Following labeling with DNA probes, a BP labeling solution was prepared containing 100 μM biotin phenol and 1 mM APS in cold 10 mM MES buffer, pH 7.4 with 10 mM MgCl2 and 10% DMSO. Labeling solution was added to cells (200 μL for 48-well plate) immediately prior to irradiation on ice for 5 minutes using photoreactor set to 50% power. After irradiation, cells were washed twice with DPBS. For fluorescence microscopy, cells were fixed with 4% formaldehyde in DPBS for 15 minutes on ice, washed thrice with cold DPBS and blocked for 10 minutes with 1% BSA in DPBS on ice. Cells were then stained with 1:500 sAv-PE (Invitrogen) in 1% BSA-DPBS for 20 minutes on ice. Cells were washed three times with DPBS prior to imaging (see Fluorescent Microscopy Imaging).
All sequences of DNA used in this paper are shown below, each named with a code of the form dna ##. Ruthenium conjugates are referred to by the original sequence and the attached Ru molecule (e.g. Ru-dna ##). /5AzideN/ and /3IAbRQSp/are codes used by the DNA supplier (Integrated DNA Technologies) to refer to azide and RQ quencher modifications on the 5′ and 3′ ends of synthetic oligonucleotides, respectively. /5Biosg/ and /3Bio/are codes used by IDT to refer to biotin modifications on the 5′ and 3′ ends of synthetic oligonucleotides, respectively.
Sequences used in
Phenanthroline-alkyne ligand was synthesized according to a procedure reported in the literature 3 using 4-pentynoic acid. 5-Amino-1,10-phenanthroline (150 mg, 0.77 mmol, 1 eq.) was dissolved in 6 mL of DCM. 4-Pentynoic acid (75 mg, 0.77 mmol, 1 eq) was then added to the mixture to create a dark orange gel. 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDCI, 295 mg, 1.54 mmol, 2.0 eq.) was then added followed by an additional 2 mL of DCM. Finally, 4-dimethylaminopyridine (DMAP, 94 mg, 0.77 mmol, 1 eq.) was added, and the reaction was stirred overnight at room temperature under N2. The reaction mixture was concentrated under reduced pressure to afford a thick yellow oil. Water was added while stirring until a white precipitate was formed. The precipitate was isolated via centrifugation at 4300 rcf for 3 minutes. The supernatant was removed, and the powder was washed once with acetonitrile followed by centrifugation. The yellow solid (160 mg, 75.8%) was analyzed via NMR in CDCl3.
1H NMR (500 MHz, CDCl3) δ 8.96 (s, 2H), 8.38 (dd, J=8.4, 1.6 Hz, 1H), 8.10-7.90 (m, 2H), 7.56-7.35 (m, 2H), 2.78 (m 2H), 2.66 (m 2H), 2.09 (s, 1H). 13C NMR (126 MHz, CDCl3) δ 170.95, 149.87, 149.65, 146.22, 144.32, 135.89, 130.79, 130.63, 128.16, 124.50, 123.39, 122.62, 120.52, 83.05, 69.88, 35.90, 14.96.
Synthesis of Ru(bpy)2(Phen-alkyne)Cl2
Phenanthroline-alkyne ligand (60 mg, 0.22 mmol, 1 eq.) was dissolved in 8 mL of ethanol and 2 mL of water. Cis-Ru(bpy)2Cl2·XH2O (113.4 mg, 0.22 mmol, 1 eq.) was then added and the reaction was degassed with bubbling nitrogen for 15 minutes. The reaction then refluxed overnight at 160° C. while under nitrogen atmosphere. After cooling to room temperature, the reaction mixture was concentrated under reduced pressure. The crude product was purified using silica gel column chromatography, eluting with MeCN:H2O:KNO3 (100:7.5:0.5). The fractions containing product were combined and concentrated under reduced pressure. The solid product was then dissolved in MeCN, while the KNO3 remained insoluble. The KNO3 was removed via vacuum filtration to yield the Ru-alkyne complex as a red solid (21.2 mg, 0.028 mmol, 12.7%). 1H and 13C NMR in MeOD. ESI-MS: expected 344.0743, observed 344.0742 m/z (+2 charge state).
1H NMR (500 MHz, MeOD) δ 8.84 (dt, J=8.6, 1.7 Hz, 1H), 8.75 (d, J=8.2 Hz, 2H), 8.71 (d, J=8.2 Hz, 2H), 8.65 (dd, J=8.4, 1.3 Hz, 1H), 8.48 (d, J=7.4 Hz, 1H), 8.24 (dd, J=5.3, 1.2 Hz, 1H), 8.21-8.13 (m, 3H), 8.08 (td, J=7.9, 1.5 Hz, 2H), 7.95 (td, J=5.1, 1.4 Hz, 2H), 7.87 (dd, J=8.5, 5.2 Hz, 1H), 7.81 (dd, J=8.3, 5.2 Hz, 1H), 7.66 (d, J=5.6 Hz, 2H), 7.56 (ddt, J=7.5, 5.6, 1.7 Hz, 2H), 7.34 (ddt, J=7.3, 5.6, 1.5 Hz, 2H), 2.88 (t, J=7.0 Hz, 2H), 2.70 (dd, J=7.0, 2.6 Hz, 2H), 2.43 (s, 1H). 13C NMR (126 MHz, MeOD) δ 172.83, 172.72, 157.41, 157.39, 157.16, 157.14, 152.26, 151.51, 151.41, 151.38, 147.93, 145.79, 137.90, 137.78, 136.45, 134.06, 133.93, 132.86, 130.68, 127.63, 127.52, 127.49, 127.45, 127.42, 126.16, 125.57, 124.23, 124.21, 124.17, 124.15, 121.73, 82.27, 69.35, 35.05, 14.17.
CuBr (50 mM, DMSO) was combined with tris-hydroxypropyltriazolylmethylamine (THPTA) (50 mM, DMSO) in a 1:4 ratio (1 μL of CuBr (50 mM) and 4 μL of THPTA (50 mM). To a 1.5 mL centrifuge tube, 1 nmol of azide modified DNA (100 μM, water) was added followed by 50 eq of CuBr complexed with THPTA and 10 eq of Ru(bpy)2(phen-alkyne) (5 mM, water). The sample was vortexed thoroughly, spun down in a bench-top centrifuge, and incubated at 37° C. for 1 hour with 300 rpm shaking while covered with foil to block light. Five identical crude reaction mixtures were combined for work-up using Amicon 3K ultra 0.5 mL devices, then diluted to 500 μL total volume with nuclease free water (NFW). Devices were spun for 8 minutes at 14,000 rcf 2 times, removing flow through and diluting to 500 μL with NFW each time. A third spin was performed for 15 minutes at 14,000 rcf. Samples were recovered by inverting the Amicon device into a clean tube and centrifuging for 2 minutes at 1,000 rcf. The conjugate was then purified by HPLC by injection of up to 5 nmol of DNA at a time. The fraction containing product was then buffer-exchanged using PBS, pH 7.4 with a second Amicon Ultra filtration device to remove residual triethyl ammonium acetate (TEAA) from the HPLC purification. Agarose gel electrophoresis was done to verify the complete removal of excess Ru-alkyne from the product. The concentration of Ru-DNA was calculated using UV-Vis absorbance at 260 and 450 nm. A standard curve of the A260 and A450 for the Ru-alkyne substrate was created (A260 extinction coefficient=21,800 cm−1 M−1, A450 extinction coefficient=10,800 cm−1 M−1), and DNA concentration was determined by subtracting the absorbance at 260 nm due to the Ru complex to find the DNA A260 contribution and using the extinction coefficient of DNA provided by IDT. To verify the identity of conjugates, intact mass analysis via electrospray mass spectrometry (ESI-MS) was performed on Ru-dna02 (see “Mass Spectrometry”). Az-dna02 had an observed mass of 6426.1902 and the Ru conjugate Ru-dna02 had an observed mass of 7113.3427. The difference of the observed masses was 687.1525 which corresponds to an m/z of 343.5763 of the +2 charge state (344.0742 m/z, +2 charge state observed for Ru(bpy)2(phen-alkyne)).
Using external stimuli to control catalysts for polymerization has garnered recent interest for its potential in additive manufacturing, patterning, and potential for controlling the microstructure of synthesized polymers. Modulating catalyst reactivity during synthesis could open routes to finely tuned microstructures, analogous to the control in bio-polymer syntheses, that are not feasible with traditional syntheses of co-polymers by timed addition of monomers and inherent monomer reactivities. In recent years, photo-controlled radical polymerization has especially garnered interest since light is an easily manipulated external stimuli, allowing spatio-temporal control. Other stimuli-responsive catalysts have used stimuli such as temperature, pH, chemical reagents, and redox state to control catalyst activity.
While there has been progress on expanding the list of stimuli ‘targets’, many of these catalysts involved significant rational design or require the target to directly modify the catalyst for activation. This leads to catalyst designs that are not easily adaptable to work with other stimuli. This is in contrast to biology which uses a broad array of stimuli including proteins, metal ions, small molecules such as hormones or nutrients (e.g. hydrocortisone, glucose), pH, etc that trigger responses or complex behavior. As a step towards bridging the gap between biological and synthetic catalysts, inventors envisioned that a hybrid biological-synthetic platform would be a promising strategy for creating a class of stimuli-responsive catalysts where the platform is readily adaptable to the types of stimuli that biological polymerization machinery responds to.
Specifically, inventors envisioned that switchable DNA scaffolded photocatalysts can be used as a generalizable platform for stimuli-responsive photocatalysts. These switchable catalysts use covalently modified DNA to control the proximity of a photocatalyst and a quencher dye. When these components are in proximity, Förster resonance energy transfer (FRET) or static quenching can occur where an excited photocatalyst transfers energy to the quencher (FRET acceptor) to undergo vibrational relaxation, preventing fluorescence or productive photocatalytic events. Controlling the proximity of the photocatalyst/quencher pair can then switch the photocatalyst between inactive and active states.
A benefit of these DNA scaffolded catalysts is that the responsive behavior originates from the DNA sequence and conformation, not the catalyst/photocatalyst itself. This allows for a potential “mix and match” where the catalyst of interest can be matched with the target specific DNA sequence. For nucleic acid type triggers (i.e. DNA and RNA strands), this scaffold follows the principles of molecular beacons. For non-nucleic acid type triggers, this scaffold takes advantage of aptamer sensors. Aptamers are sequences of nucleic acids that fold into specific conformations that allow binding of targets. Aptamers are capable of targeting a wide range of analytes from simple ions to small molecules to entire proteins. While there are already thousands of published sequences of aptamers, 12 new sequences for novel targets can be found through a process called systematic evolution of ligands by exponential enrichment (SELEX). Some of the most common approaches for sensor development from aptamers already involve the attachment of a fluorophore to the target binding DNA sequence and the partial hybridization of another DNA oligomer modified with a quencher dye. The partial hybridization brings the quencher dye into proximity of the fluorophore, allowing FRET to occur. Upon binding of the target, a conformational change in the DNA secondary structure disrupts the partial hybridization and removes the proximity of the fluorophore/quencher pair. Aptamer sensors can be developed to incorporate fluorophore/quencher pairs directly as part of the SELEX discovery process or by modifying existing aptamer sequences. These fluorescent sensors have been used for the detection of analytes and as probes in biological systems, but reports using aptamer sensors as switchable photocatalysts are primarily limited to the production of reactive oxygen species.
As an initial demonstration, inventors explored the bulk formation of a hydrogel through uncontrolled radical polymerization. This offered a sensitive detection method with an easily identified macroscopic output. Inventors explored reported aptamer sensors that targeted a range of analytes from DNA to ions to small molecules. A wide range of analyte types were chosen to demonstrate the generalizability of the chemical stimuli for this approach. Fluorescein modified DNA aptamers were commercially ordered since this was the most commonly used fluorophore in these systems. While fluorescein is predominately used as a fluorophore, it can act as a photocatalyst, albeit less potent than structurally similar photocatalysts such as Eosin Y.
DNA aptamer sensors were dissolved in buffer and a reaction solution containing 25% v/v poly-ethylene glycol (Mn-700) diacrylate (PEGDA), 210 mM triethanolamine, and 35 mM N-Vinylpyrrolidone. The kinetics of DNA conformational switching were rapid and similar for the reaction conditions and fully aqueous buffer conditions.
To demonstrate the specificity for the desired target, the switchable DNA catalyst for hydrocortisone was tested against the presence of all other targets and a structurally similar steroid, deoxycholic acid.
After validating photocatalytic turn-on using DNA aptamers and a range of target analytes, inventors aimed to demonstrate switchable polymerization activity on living cells. Polymer coatings on the surface of living cells have potential applications such as cell encapsulation/capture, functional cell coatings, and labeling through signal amplification. Inventors anchored a DNA ‘molecular hook’ scaffold to yeast cells through covalent labeling of nucleophilic residues using NHS-biotin followed by a streptavidin-biotin sandwich assay with a biotin modified DNA anchor strand (see
The same constructs were made but with fluorescein photocatalyst instead of Cy5 fluorophore. Cells labeled with the fluorescein scaffolds were suspended in a similar solution of PEGDA monomer to test for bulk hydrogel formation.
While the uncontrolled radical polymerizations demonstrated above offer a sensitive detection method, controlled radical polymerization techniques, such as reversible addition fragmentation chain-transfer (RAFT) polymerization, can be used for the synthesis of complex polymer architectures (e.g. block copolymers) and for modifying the surfaces of materials or even living cells. RAFT controls the chain growth of polymers through a reversible-deactivation process using chain transfer agents. This allows for targeted molecular weights, predictable growth kinetics, relatively narrow molecular weight distributions, and high end-group fidelity to be achieved. Combining photochemistry with RAFT, photoinduced electron/energy transfer-RAFT (PET-RAFT) is a type of photocontrolled polymerization that allows spatio-temporal control of polymer synthesis. Recent advances in PET-RAFT have demonstrated compatibility with aqueous conditions, ambient oxygen, biomolecules such as proteins and DNA, and even live cell surfaces. While PET-RAFT and similar photo-controlled polymerizations have myriad applications, there has been little work exploring other stimuli or dual-gated systems beyond light and pH or temperature.
Inventors used the hybridization of DNA to reversibly activate and deactivate a photocatalyst during a PET-RAFT polymerization (
In summary, inventors demonstrated a modular platform to generate switchable photocatalysts for polymerizations using a DNA scaffolded system that depends on the DNA sequence and conformational state to control catalysis rather than the inherent properties of the catalyst. Inventors expect that DNA aptamer sensors modified with potent photocatalysts can be used as a dual-gated system for photocontrolled polymerization where the biological/chemical signal is as generalizable as aptamer targets. Inventors expect that these switchable photocatalysts can be designed for complex responses such as the growth of polymer coatings on whole or sub-regions of cells for specific chemical targets. The union of photocatalysis with DNA scaffolds and aptamers demonstrates a near limitless number of chemical stimuli can be used to tune the activation of catalysis, taking one step closer to mimicking the complicated signaling that is important in biological systems. Future studies will be aimed towards applications of this system on the surface of living cells for creating unique surface modifications and coatings.
The present application claims priority to U.S. Provisional Patent Application No. 63/275,722 filed Nov. 4, 2021, the entire contents of which are hereby incorporated by reference.
This invention was made with government support under W911NF-21-1-0073 awarded by the ARMY/ARO. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63275722 | Nov 2021 | US |
