Patent Grant
9181326
This invention provides methods, reagents and kits for analyzing polypeptides and their modifications from biological samples. In particular, the invention provides compositions, kits and methods for detecting ubiquitinated polypeptides and ubiquitination sites in proteins.
Personalized medicine is the application of genomic and molecular data to better target the delivery of health care to specific patients, facilitate the discovery and clinical testing of new products, and help determine a person's predisposition to a particular disease or condition.
On a technical level, personalized medicine depends on the identification and detection of proteins, genes and genetic variation (“biomarkers”) that play a role in a given disease. Rodland, Clin Biochem. 2004 July; 37(7):579-83. The presence or absence of certain biomarkers is then correlated with the incidence of a particular disease or disease predisposition. However, currently available methods for biomarker analysis are associated with long waiting periods, high cost and numerous technical hurdles.
The current standard for protein detection and/or quantification is based on immunoreactive detection (Western analysis). However, this technique requires the availability of an appropriately specific antibody. In addition, many antibodies only recognize proteins in an unfolded (denatured) form, cross-reactivity can be severely limiting, and quantification is generally relative.
The development of methods and instrumentation for automated, data-dependent electrospray ionization (ESI) tandem mass spectrometry (MS/MS) in conjunction with microcapillary liquid chromatography (LC) and database searching has significantly increased the sensitivity and speed of the identification of gel-separated proteins. Microcapillary LC-MS/MS has been used successfully for the large-scale identification of individual proteins directly from mixtures without gel electrophoretic separation (Link et al., 1999; Opitek et al., 1997). However, while these approaches accelerate protein identification, quantities of the analyzed proteins cannot be easily determined, and these methods have not been shown to substantially alleviate the dynamic range problem also encountered by the 2DE/MS/NIS approach. Therefore, low abundance proteins in complex samples are also difficult to analyze by the microcapillary LC/MS/MS method without their prior enrichment.
Protein ubiquitination is the one of the most common of all post-translational modifications. Ubiquitin is a highly conserved 76 amino acid protein which is linked to a protein target after a cascade of transfer reactions. Ubiquitin is activated through the formation of a thioester bond between its C-terminal glycine and the active site cysteine of the ubiquitin activating protein, E1 (Hershko, 1991, Trends Biochem. Sci. 16(7): 265-8). In subsequent trans-thiolation reactions, Ubiquitin is transferred to a cysteine residue on a ubiquitin conjugating enzyme, E2 (Hershko, et al., 1983, J. Biol. Chem. 267: 8807-8812). In conjunction with E3, a ubiquitin polypeptide ligase, E2 then transfers ubiquitin to a specific polypeptide target (see, e.g., Scheffner, et al., 1995, Nature 373(6509): 81-3), forming an isopeptide bond between the C-terminal glycine of ubiquitin and the 8-amino group of a lysine present in the target (See
The covalent attachment of ubiquitin to cellular polypeptides, in most cases, marks them for degradation by a multi-polypeptide complex called a proteosome. The ubiquitinproteosome system is the principal mechanism for the turnover of short-lived polypeptides, including regulatory polypeptides (Weissman, 2001, Nat. Rev. Mol. Cell. Biol. 2: 169-78). Some known targets of ubiquitination include: cyclins, cyclin-dependent kinases (CDK's), NFKB, cystic fibrosis transduction receptor, p53, ornithine decarboxylase (ODC), 7-membrane spanning receptors, Cdc25 (phosphotyrosme phosphatase), Rb, Ga, c-Jun and c-Fos. Polypeptides sharing consensus sequences such as PEST sequences, destruction boxes, and F-boxes generally are also targets for ubiquitin-mediated degradation pathways (see, e.g., Rogers, et al., 1986, Science 234: 364-368; Yamano, et al., 1998, The EMBO Journal 17: 5670-5678; Bai, et al., 1996, Cell 86: 263-274).
Ubiquitin has been implicated in a number of cellular processes including: signal transduction, cell-cycle progression, receptor-mediated endocytosis, transcription, organelle biogenesis, spermatogenesis, response to cell stress, DNA repair, differentiation, programmed cell death, and immune responses (e.g., inflammation). Ubiquitin also has been implicated in the biogenesis of ribosomes, nucleosomes, peroxisomes and myofibrils. Thus, ubiquitin can function both as signal for polypeptide degradation and as a chaperone for promoting the formation of organelles (see, e.g., Fujimuro, et al., 1997, Eur. J. Biochem. 249: 427-433).
Deregulation of ubiquitination has been implicated in the pathogenesis of many different diseases. For example, abnormal accumulations of ubiquitinated species are found in patients with neurodegenerative diseases such as Alzheimer's as well as in patients with cell proliferative diseases, such as cancer (see, e.g., Hershko and Ciechanover, 1998, Annu Rev. Biochem. 67: 425-79; Layfield, et al., 2001, Neuropathol. Appl. Neurobiol. 27:171-9; Weissman, 1997, Immunology Today 18(4): 189).
While the importance of its biological role is well appreciated, the ubiquitin pathway is inherently difficult to study. Generally, studies of ubiquitination have focused on particular polypeptides. For example, site-directed mutagenesis has been used to evaluate critical amino acids which form the “destruction boxes”, or “D-boxes”, of cyclin, sites which are rapidly poly-ubiquitinated when cyclin is triggered for destruction. See, e.g., Yamano, et al., 1998, The EMBO Journal 17: 5670-5678; Amon et al., 1994, Cell 77: 1037-1050; Glotzer, et al., 1991, Nature 349: 132-138; King, et al., 1996, Mol. Biol. Cell 7:1343. Corsi, et al., 1997, J. Biol. Chem. 272(5): 2977-2883, which describe a Western blotting approach to identify ubiquitination sites. In this technique, crude radiolabeled a-spectrin fractions were ubiquitinated in vitro, digested with proteases, and electrophoresed on gels. Ubiquitinated peptides were identified by their differences in mass from peptides generated by digestion of non-ubiquitinated α-spectrin.
Although mass spectrometry offers a powerful tool for identifying ubiquitin substrates, a number of unresolved issues remain. Despite many advances, MS data is inherently biased toward more abundant substrates. The effects of ubiquitin epitope tags used to enriched ubiquinated proteins remain incompletely understood, including whether purification biases exist and whether ubiquitin pathway enzymes utilize tagged and wild-type ubiquitin with equal efficiency. It is also not clear if ubiquitin-binding proteins or ubiquitin antibodies may work efficiently as affinity reagents in order to lessen the need for epitope. Kirkpatrick et al., Nat Cell Biol. 2005 August; 7(8): 750-757.
One aspect of the invention relates to a method for determining the presence of at least one ubiquitinated polypeptide in a biological sample comprising: Contacting the sample with at least one hydrolyzing agent, wherein the hydrolyzing agent is capable of cleaving a ubiquitinated polypeptide to produce at least one ubiquitin remnant peptide, to obtain a hydrolyzed sample; Contacting the hydrolyzed sample with a substrate comprising an at least one immobilized binding partner; wherein the at least one immobilized binding partner preferentially binds a ubiquitin remnant peptide over a peptide having the same amino acid sequence as the ubiquitin remnant peptide but lacking a ubiquitin remnant; Removing the hydrolyzed sample from the substrate in a manner such that the at least one ubiquitin remnant peptide would remain bound to the immobilized binding partner; Contacting the substrate with an elution solution, wherein the least one ubiquitin remnant peptide would dissociate from the immobilized binding partner into the elution solution; and Determining the presence of a least one ubiquitinated polypeptide in the biological sample when the elution solution contains the at least one least ubiquitin remnant peptide.
In one embodiment of this aspect of the invention the determining is performed by LC, MS and preferably LC-MS/MS. In a further embodiment, the amino acid sequence of at least one ubiquitin remnant peptide present in the elution solution, is determined. In yet another embodiment, the sequence is compared to the sequence of the ubiquitinated polypeptide and the site of ubiquitination in the ubiquitinated polypeptide is thereby determined. In still a further embodiment, the elution solution further comprises at least one standard peptide, wherein the at least one standard peptide has the substantially the same amino acid sequence as the at least one distinct peptide but a different measured accurate mass.
Another aspect of the invention relates to an isolated antibody that preferentially binds a ubiquitin remnant peptide over a peptide having the same amino acid sequence as the ubiquitin remnant peptide but lacking a ubiquitin remnant. In one embodiment, the antibody is a monoclonal antibody. In another embodiment, the antibody is a polyclonal antibody. In still yet another embodiment, the antibody is selected from the group consisting of single chain Fvs (scFvs), Fab fragments, Fab′ fragments, F(ab′) 2, disulfide linked Fvs (sdFvs), Fvs, and fragments thereof. In yet another embodiment, the antibody comprises a polypeptide of SEQ ID NO: 1. In a further embodiment, the antibody comprises a polypeptide of SEQ ID NO: 2. In yet another embodiment, the antibody comprises a light chain polypeptide of SEQ ID NO: 2 and a heavy chain polypeptide of SEQ ID NO: 1. In still another embodiment, the antibody comprises an antigen binding site comprising the variable region of the heavy chain set forth in SEQ ID NO: 1. In still a further embodiment, the antibody comprises an antigen binding site comprising the variable region of the light chain set forth in SEQ ID NO: 2.
Another aspect of the invention relates to an isolated nucleic acid encoding an antibody that preferentially binds a ubiquitin remnant peptide over a peptide having the same amino acid sequence as the ubiquitin remnant peptide but lacking a ubiquitin remnant.
A further aspect of the invention relates to a cell comprising a nucleic acid, preferably in the form of a vector, that encodes an antibody that preferentially binds a ubiquitin remnant peptide over a peptide having the same amino acid sequence as the ubiquitin remnant peptide but lacking a ubiquitin remnant.
Another aspect of the invention relates to the isolated ubiquitin remnant peptides listed in Table 4 and fragments and variants thereof.
Another aspect of the invention relates to nucleic acids encoding the ubiquitin remnant peptides listed in Table 4 and fragments and variants thereof.
Yet a further aspect of the invention relates to a method for determining whether a patient is has or is likely to have or develop a disease associated with a least one ubiquitinated polypeptide comprising: obtaining a biological sample from the patient; Contacting the sample with at least one hydrolyzing agent, wherein the hydrolyzing agent is capable of cleaving a ubiquitinated polypeptide to produce at least one ubiquitin remnant peptide, to obtain a hydrolyzed sample; Contacting the hydrolyzed sample with a substrate comprising an at least one immobilized binding partner; wherein the at least one immobilized binding partner preferentially binds a ubiquitin remnant peptide over a peptide having the same amino acid sequence as the ubiquitin remnant peptide but lacking a ubiquitin remnant; Removing the hydrolyzed sample from the substrate in a manner such that the at least one ubiquitin remnant peptide would remain bound to the immobilized binding partner; Contacting the substrate with an elution solution, where in the least one ubiquitin remnant peptide would dissociate from the immobilized binding partner into the elution solution; and Determining the presence of a least one ubiquitinated polypeptide in the biological sample when the elution solution contains the at least one least ubiquitin remnant peptide; Determining that the patient is has or is likely to have or develop the disease associated with a least one ubiquitinated polypeptide if the least one ubiquitinated polypeptide is present in the biological sample.
Another aspect of the invention relates to a method for determining whether a disease is associated with at least one ubiquitinated polypeptide comprising Obtaining a biological sample from a patient having the disease; Contacting the sample with at least one hydrolyzing agent, wherein the hydrolyzing agent is capable of cleaving a ubiquitinated polypeptide to produce at least one ubiquitin remnant peptide, to obtain a hydrolyzed sample; Contacting the hydrolyzed sample with a substrate comprising an at least one immobilized binding partner; wherein the at least one immobilized binding partner preferentially binds a ubiquitin remnant peptide over a peptide having the same amino acid sequence as the ubiquitin remnant peptide but lacking a ubiquitin remnant; Removing the hydrolyzed sample from the substrate in a manner such that the at least one ubiquitin remnant peptide would remain bound to the immobilized binding partner; Contacting the substrate with an elution solution, where in the least one ubiquitin remnant peptide would dissociate from the immobilized binding partner into the elution solution; Determining the presence of a least one ubiquitinated polypeptide in the biological sample when the elution solution contains the at least one least ubiquitin remnant peptide; and Determining that the disease is associated with the presence of the at least one ubiquitinated polypeptide if the least one ubiquitinated polypeptide is absent in the biological sample of a healthy individual.
Still another aspect of the invention relates to a method for determining whether a disease is associated with at least one ubiquitin remnant peptide Obtaining a biological sample from a patient having the disease to obtain a disease biological sample; Obtaining a biological sample from a healthy patient to obtains a healthy biological sample; Contacting the disease biological sample with at least one hydrolyzing agent, wherein the hydrolyzing agent is capable of cleaving a ubiquitinated polypeptide to produce the least one ubiquitin remnant peptide, to obtain a disease hydrolyzed sample; Contacting the healthy biological sample with at least one hydrolyzing agent, wherein the hydrolyzing agent is capable of cleaving a ubiquitinated polypeptide to produce the least one ubiquitin remnant peptide, to obtain a healthy hydrolyzed sample; Contacting the disease hydrolyzed sample with a substrate comprising an at least one immobilized binding partner; wherein the at least one immobilized binding partner preferentially binds a ubiquitin remnant peptide over a peptide having the same amino acid sequence as the ubiquitin remnant peptide but lacking a ubiquitin remnant; Removing the disease hydrolyzed sample from the substrate in a manner such that the at least one ubiquitin remnant peptide would remain bound to the immobilized binding partner; Contacting the substrate with an elution solution, where in the least one ubiquitin remnant peptide would dissociate from the immobilized binding partner into the elution solution; and Determining the presence of the a least one ubiquitin remnant peptide in the elution solution; Determining that the disease is associated with the presence of the at least one ubiquitin remnant peptide if the least one ubiquitin remnant peptide is absent in the healthy biological sample.
A more complete understanding of the present invention may be obtained by reference to the accompanying drawings, when considered in conjunction with the subsequent detailed description. The embodiments illustrated in the drawings are intended only to exemplify the invention and should not be construed as limiting the invention to the illustrated embodiments, in which:
The inventors have discovered antibody reagents that specifically bind peptides carrying a ubiquitin remnant from a digested or chemically treated biological sample. See also U.S. application Ser. No. 12/455,496 (which is incorporated by reference in its entirety for all purposes and without limitation).
These reagents allow the technician to identify ubiquitinated polypeptides as well as the sites of ubiquitination on them. The reagents are preferably employed in proteomic analysis using mass spectrometry. The antibody reagents (in both polyclonal and monoclonal form) specifically bind the remnant of ubiquitination, i.e., a diglycine modified epsilon amine of lysine left on a peptide which as been generated by digesting or chemically treating ubiquitinated proteins. The inventive antibody reagents' affinity to the ubiquitin remnant does not depend on the remaining amino acid sequences flanking the modified lysine, i.e., they are “context independent”. In addition, the antibodies of the invention do not cross react with peptides lacking the ubiquitin remnant. See for example, U.S. Pat. Nos. 6,441,140; 6,982,318; 7,198,896; 7,259,022; 7,300,753; 7,344,714; U.S. Ser. No. 11,484,485, all herein incorporated by reference in their entirety.
Notwithstanding the low abundance of ubiquitinated polypeptides in biological samples, the invention allows for high-throughput MS identification of ubiquitination sites. Immunoaffinity purification (IAP) with the inventive antibodies enrich those ubiquitinated peptides derived from the ubiquitinated portion of polypeptides relative to peptides lacking ubiquitination sites, as well as peptides from proteins which strongly interact with ubiquitin or ubiquitinated proteins, thereby significantly reducing the complexity of the peptide mixture. The purified digest sample can be directly applied to tandem MS for efficient peptide sequence analysis and protein identification to reveal ubiquitinated polypeptides and their sites of ubiquitination.
Prior to describing various embodiments of the current invention, the following definitions are provided:
As used herein the term “peptide” or “polypeptide” refers to a polymer formed from the linking, in a defined order, of preferably, α-amino acids, D-, L-amino acids, and combinations thereof. The link between one amino acid residue and the next is referred to as an amide bond or a peptide bond. Proteins are polypeptide molecules (or having multiple polypeptide subunits). The distinction is that peptides are preferably short and polypeptides/proteins are preferably longer amino acid chains. The term “protein” is intended to also encompass derivatized molecules such as glycoproteins and lipoproteins as well as lower molecular weight polypeptides.
As used herein, the term “ubiquitinated polypeptide” refers to a polypeptide bound to ubiquitin, a ubiquitin-like protein (e.g., NEDD8 or ISG15) or a portion thereof. Preferably, ubiquitination is the formation an isopeptide bond between the C-terminal glycine of ubiquitin (or ubiquitin-like protein see e.g., J Proteome Res. 2008 March; 7(3):1274-87) and the 8-amino group of a lysine present in the target. (See e.g.,
As used herein, a “ubiquitin remnant” or a “ubiquitin tag” is that portion of a ubiquitinated polypeptide which remains attached to the digestion product of the ubiquitinated polypeptide which has been exposed to a hydrolyzing agent such as trypsin. Preferably, the ubiquitin remnant is a diglycine modified epsilon amine of lysine, which adds about 114 daltons to the mass of the lysine residue (see
A “ubiquitin remnant peptide” is the product that results from the digestion of a ubiquitinated polypeptide with a hydrolyzing agent such as trypsin, i.e., a peptide containing at least one ubiquitin remnant. In the preferred embodiment of the invention, a binding partner is used that specifically recognizes and binds to a ubiquitin remnant peptide but does not cross react with other peptides having the same amino acid sequence but which lack the ubiquitin remnant. The preferred binding partner is an antiubiquitin remnant peptide antibody or fragment thereof.
The invention also encompasses the novel ubiquitin remnant peptides disclosed herein in Table 4 as well as fragments and variants thereof.
The term “variant” as used herein relative to ubiquitin remnant peptides, refers to a peptide having a ubiquitin remnant that possesses a similar or identical amino acid sequence as a ubiquitin remnant peptide (e.g., one disclosed in Table 4). A variant having a similar amino acid sequence refers to a peptide comprising, or alternatively
consisting of, an amino acid sequence that is at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98% or at least 99% identical to the predicate ubiquitin remnant peptide. Peptide variants also include those having a deletion, substitution and/or addition of about 1 to about 2; about 1 to about 3; or about 1 to about 4 amino acids relative to the
predicate ubiquitin remnant peptide.
To determine the percent identity of two amino acid sequences or of two nucleic acid sequences, the sequences are aligned for optimal comparison purposes (e.g., gaps can be introduced in the sequence of a first amino acid or nucleic acid sequence for optimal alignment with a second amino acid or nucleic acid sequence). The amino acid residues or nucleotides at corresponding amino acid positions or nucleotide positions are then compared. When a position in the first sequence is occupied by the same amino acid residue or nucleotide at the corresponding position in the second sequence, then the molecules are identical at that position. The percent identity between the two sequences is a function of the number of identical positions shared by the sequences (i.e., % identity number of identical overlapping positions/total number of positions.times.100%). In one embodiment, the two sequences are the same length.
The term “fragment” as used herein refers to a peptide comprising a ubiquitin remnant and an amino acid sequence of at least 3 amino acid residues, at least 5 amino acid residues, at least 7 amino acid residues, at least 10 amino acid residues, at least 15 amino acid residues, at least 20 amino acid residues, at least 25 amino acid residues, at least 30 amino acid residues of a ubiquitin remnant peptide.
The invention also includes nucleic acids that encode for the ubiquitin remnant peptides disclosed herein in Table 4 as well as fragments and variants thereof.
As used herein, the term “biological sample” refers to a readily obtainable mixture of a plurality of polypeptides present in varying concentrations. Preferred biological samples have about 5,000 to about 20,000 different polypeptides. More preferably, biological samples have about 7,500 to about 15,000 different polypeptides. Most preferably, biological samples have about 10,000 different polypeptides. Generally, such samples are environmental, industrial, veterinary or medical in origin and from an animal, plant, a bacterium, a fungus, a protist or a virus. The preferred biological samples include but are not limited to saliva, mucous, tears, blood, serum, lymph/interstitial fluids, buccal cells, mucosal cells, cerebrospinal fluid, semen, feces, plasma, urine, a suspension of cells, or a suspension of cells and viruses. The most preferred biological samples are mammalian, more preferably human, serum and urine.
Where the biological sample is blood, serum or lymph/interstitial fluid, the invention envisages an optional step of depleting the biological sample of common and disproportionally over-represented background proteins not suspected of being associated with ubiquitinated polypeptides. Such proteins include but are not limited to albumin, IgG, IgA, transferrin, haptoglobin, and anti-trypsin; or combinations thereof. The skilled artisan will recognized that such a step is carried out by basic affinity chromatography techniques. As used here in the term “depleted” or “depleting” means markedly lessening the concentration of a particular species in a solution, e.g., by more than or about 50%; more than or about 60%; more than or about 65%; more than or about 70%; more than or about 75%; more than or about 80%; more than or about 85%; more than or about 90%; more than or about 92%; more than or about 95%; more than or about 97%; more than or about 98%; more than or about 99%. Alternatively the biological sample may be a subcellular fraction of a cell line or tissue, enriched for specific cellular organelles such as nuclei, cytoplasm, plasma membranes, mitochondria, internal membrane structures, Golgi apparatus, endoplasmic reticulum, etc. or specific tissue organelles such as post-synaptic densities from brain, islets from pancreas, etc.
As used herein, the term “hydrolyzing agent” refers to any one or combination of a large number of different enzymes, including but not limited to trypsin, Lysine-C endopeptidase (LysC), arginine-C endopeptidase (ArgC), Asp-N, glutamic acid endopeptidase (GluC) and chymotrypsin, V8 protease and the like, as well as chemicals, such as cyanogen bromide. In the subject invention one or a combination of hydrolyzing agents cleave peptide bonds in a protein or polypeptide, in a sequence-specific manner, generating a predictable collection of shorter peptides (a “digest”). A portion of the biological samples are contacted with hydrolyzing agent(s) to form a digest of the biological sample. Given that the amino acid sequences of certain polypeptides and proteins in biological samples are often known and that the hydrolyzing agent(s) cuts in a sequence-specific manner, the shorter peptides in the digest are generally of a predicable amino acid sequence. Preferably, the treatment of a polypeptide with a hydrolyzing agents results in about 2 to about 20, more preferably about 5 to about 15 and most preferably about 10 peptides. If the polypeptide in a biological sample is a ubiquitinated polypeptide, at least one of the resulting peptides in the digest will be a ubiquitin remnant peptide. The preferred hydrolyzing agent is a protease, or chemical which cleaves ubiquitinated proteins in a manner that results in the formation of at least one ubiquitin remnant peptide. Most preferably, the protease is trypsin.
The term “mass spectrometer” means a device capable of detecting specific molecular species and measuring their accurate masses. The term is meant to include any molecular detector into which a polypeptide or peptide may be eluted for detection and/or characterization. In the preferred MS procedure, a sample, e.g., the elution solution, is loaded onto the MS instrument, and undergoes vaporization. The components of the sample are ionized by one of a variety of methods (e.g., by electrospray ionization or “ESI”), which results in the formation of positively charged particles (ions). The positive ions are then accelerated by a magnetic field. The computation of the mass-to-charge ratio of the particles is based on the details of motion of the ions as they transit through electromagnetic fields, and detection of the ions. The preferred mass measurement error of a mass spectrometer of the invention is 10 ppm or less, more preferable is 7 ppm or less; and most preferably 5 ppm or less.
Fragment ions in the MS/MS and MS3 spectra are generally highly specific and diagnostic for peptides of interest. In contrast, to prior art methods, the identification of peptide diagnostic signatures provides for a way to perform highly selective analysis of a complex protein mixture, such as a cellular lysate in which there may be greater than about 100, about 1000, about 10,000, or even about 100,000 different kinds of proteins. Thus, while conventional mass spectroscopy would not be able to distinguish between peptides with different sequences but similar m/z ratios (which would tend to co-elute with any labeled standard being analyzed), the use of peptide fragmentation methods and multistage mass spectrometry in conjunction with LC methods, provide a way to detect and quantify target proteins which are only a small fraction of a complex mixture (e.g., present in less than 2000 copies per cell or less than about 0.001% of total cellular protein) through these diagnostic signatures.
Test peptides are preferably examined by monitoring of a selected reaction in the mass spectrometer. This involves using the prior knowledge gained by the characterization of a standard peptide and then requiring the mass spectrometer to continuously monitor a specific ion in the MS/MS or MS spectrum for both the peptide of interest and the standard peptide. After elution, the areas-under-the-curve (AUC) for both the standard peptide and target peptide peaks may be calculated. The ratio of the two areas provides the absolute quantification that may then be normalized for the number of cells used in the analysis and the protein's molecular weight, to provide the precise number of copies of the protein per cell.
As used herein the term, “accurate mass” refers to an experimentally or theoretically determined mass of an ion that is used to determine an elemental formula. For ions containing combinations of the elements C, H, N, O, P, S, and the halogens, with mass less than 200 Unified Atomic Mass Units, a measurement about 5 ppm uncertainty is sufficient to uniquely determine the elemental composition.
As used herein the term, “predetermined peptide accurate mass” refers to the experimentally determined or calculated accurate mass of a peptide with a known amino acid sequence (along with any associated post-translational modifications). The accurate mass of any such specific amino acid sequence may be readily calculated by one of skill in the art.
As used herein, “a peptide fragmentation signature” refers to the distribution of mass-to-charge ratios of fragmented peptide ions obtained from fragmenting a peptide, for example, by collision induced disassociation, ECD, LID, PSD, IRNPD, SID, and other fragmentation methods. A peptide fragmentation signature which is “diagnostic” or a “diagnostic signature” of a target protein or target polypeptide is one which is reproducibly observed when a peptide digestion product of a target protein/polypeptide identical in sequence to the peptide portion of a standard peptide, is fragmented and which differs only from the fragmentation pattern of the standard peptide by the mass of the mass-altering label and/or the presence of a ubiquitin remnant. Preferably, a diagnostic signature is unique to the target protein (i.e., the specificity of the assay is at least about 95%, at least about 99%, and preferably, approaches 100%).
The term “substrate” includes any solid support or phase upon which a binding partner may be immobilized. Preferred supports are those well known in the art of affinity chromatography for example but not limited to polymeric and optionally magnetic beads, polystyrene, sepharose or agarose gel matrices, or nitrocellulose membranes.
The term “binding partner” refers to any of a large number of different molecules or aggregates. Preferably, a binding partner functions by binding to a polypeptide or peptide in order to enrich it prior to analysis, e.g., by MS, LC-MS, or LC-MS/MS. Preferably, binding partners bind ubiquitin remnant peptides to enrich in a digest. Proteins, polypeptides, peptides, nucleic acids (oligonucleotides and polynucleotides), antibodies, ligands, polysaccharides, microorganisms, receptors, antibiotics, and test compounds (particularly those produced by combinatorial chemistry) may each be a binding partner.
In the preferred one embodiment, the binding partner is immobilized by being directly or indirectly, covalently or non-covalently bound to the substrate. In another embodiment, the binding partner does not require a substrate and can be used to immuno-precipitate the ubiquitin remnant peptides for example. In a further embodiment, the binding partner can be used to bind ubiquitin remnant peptides in solution. The technician could then enrich for ubiquitin remnant peptides by filtering ubiquitin remnant peptide-binding partner complexes, through size cut-off or size exclusion chromatography for example.
The preferred binding partner is a “ubiquitin remnant peptide specific antibody” or an “anti-ubiquitin remnant antibody” which specifically yet reversibly binds ubiquitin remnant peptides and does not bind (i.e., cross react with) peptides having the same amino acid sequence but which lack the ubiquitin remnant. As such, the preferred ubiquitin remnant peptide-specific antibodies bind ubiquitin remnant peptides in a context independent manner.
Accordingly, the invention provides an isolated antibody or binding partner that preferentially binds a ubiquitin remnant peptide over a peptide having the same amino acid sequence as the ubiquitin remnant peptide but lacks the ubiquitin remnant. In some embodiments, the isolated antibody or binding partner specifically binds a ubiquitin remnant peptide but does not specifically bind a peptide having the same amino acid sequence as the ubiquitin remnant peptide but lacks the ubiquitin remnant. As used herein, by “specifically binds” is meant that a binding partner or an antibody of the invention interacts with its target molecule (e.g., a ubiquitin remnant peptide), where the interaction is dependent upon the presence of a particular structure (e.g., the antigenic determinant or epitope on the peptide); in other words, the reagent is recognizing and binding to a specific polypeptide structure rather than to all polypeptides in general. In some embodiments, the isolated antibodies or isolated binding partners do not specifically bind to a peptide having the same amino acid sequence as the ubiquitin remnant peptide but lacks the ubiquitin remnant.
The isolated antibodies and/or isolated binding partners of the invention can be used in the methods of the invention.
It should be understood that the substrate can have a number many different binding partners having a different binding specificity for a different polypeptide, peptide, subiquitin remnant peptide or epitopes thereof. As such, binding partners might be derived from monoclonal sources or polyclonal sera. Preferably, the substrate has about 2 to about 500, more preferably about 5 to about 400, even more preferably about 10 to about 300 and most preferably about 15 to about 200, yet even more preferably about 20 to about 100, about 25 to about 75 and about 30 to about 60 different binding partners each specifically binding to a different and/or distinct peptide. This allows the technician to simultaneously process and analyze the biological sample for the presence of a large number of polypeptides in a manner not feasible with multiplex PCR or ELISA techniques. Additional methods and reagents for immunoaffinity purification and/or enrichment of peptides containing certain motifs such as the ubiquitin remnant may be found in e.g., in U.S. Pat. Nos. 7,198,896 and 7,300,753.
The term “antibody” as used herein, refers to immunoglobulin molecules and immunologically active portions of immunoglobulin molecules, i.e., molecules that contain an antigen binding site that specifically binds to an antigen. As such, the term antibody encompasses not only whole antibody molecules, but also antibody multimers and antibody fragments, as well as variants (including derivatives) of antibodies, antibody multimers and antibody fragments. The preferred antibody disclosed herein is referred to as D4A7A10.
The basic antibody structural unit is known to comprise a tetramer. Each tetramer is composed of two identical pairs of polypeptide chains, each pair having one “light” (about 25 kilodalton) and one “heavy” chain (about 50-70 kilodalton).
The amino-terminal portion of each chain includes a variable region of about, 80, 85, 90, 95, 100, 105, preferably 100 to 110 or more amino acids primarily responsible for antigen recognition. Herein the terms “heavy chain” and “light chain” refer to the heavy and light chains of an antibody unless otherwise specified. The amino acid sequence of the D4A7A10 heavy chain is set forth in SEQ ID NO: 1. The amino acid sequence of the D4A7A10 light chain is set forth in SEQ ID NO: 2.
The carboxy-terminal portion of each chain preferably defines a constant region primarily responsible for effector function. Human light chains are classified as kappa and lambda light chains. Heavy chains are classified as mu, delta, gamma, alpha, or epsilon, and define the antibody's isotype as IgM, IgD, IgG, IgA, and IgE, respectively. See generally, Fundamental Immunology Ch. 7 (Paul, W., ed., 2nd ed. Raven Press, N.Y. (1989)) (incorporated by reference in its entirety for all purposes). The variable regions of each light (“VL”)/heavy chain (“VH”) pair preferably form the antibody binding site. Thus, an intact IgG antibody has two binding sites. Except in bifunctional or bispecific antibodies, the two binding sites are the same. The chains all exhibit the same general structure of relatively conserved framework regions (FR) joined by three hyper variable regions, also called complementarity determining regions or CDRs. The CDRs from the heavy and the light chains of each pair are aligned by the framework regions, enabling binding to a specific epitope. From N-terminal to C-terminal, both light and heavy chains comprise the domains FR1, CDR1, FR2, CDR2, FR3, CDR3 and FR4. The assignment of amino acids to each domain is in accordance with the definitions of Kabat Sequences of Proteins of Immunological Interest (National Institutes of Health, Bethesda, Md. (1987 and 1991)), or Chothia & Lesk, J. Mol. Biol. 196:901-917 (1987); Chothia et al., Nature 342:878-883 (1989).
A bispecific or bifunctional antibody is an artificial hybrid antibody having two different heavy/light chain pairs and two different binding sites. Bispecific antibodies can be produced by a variety of methods including fusion of hybridomas or linking of Fab′ fragments. See, e.g., Songsivilai & Lachmann Clin. Exp. Immunol. 79: 315-321 (1990), Kostelny et al. J. Immunol. 148:1547 1553 (1992). In addition, bispecific antibodies may be formed as “diabodies” (Holliger et al. “‘Diabodies’: small bivalent and bispecific antibody fragments” PNAS USA 90:6444-6448 (1993)) or “Janusins” (Traunecker et al. “Bispecific single chain molecules (Janusins) target cytotoxic lymphocytes on HIV infected cells” EMBO J. 10:3655-3659 (1991) and Traunecker et al. “Janusin: new molecular design for bispecific reagents” Int J Cancer Suppl 7:51-52 (1992)). Production of bispecific antibodies can be a relatively labor intensive process compared with production of conventional antibodies and yields and degree of purity are generally lower for bispecific antibodies.
Examples of molecules which are described by the term “antibody” herein include, but are not limited to: single chain Fvs (sdFvs), Fab fragments, Fab′ fragments, F(ab′)2, disulfide linked Fvs (sdFvs), Fvs, and fragments thereof comprising or alternatively consisting of, either a VL or a VH domain. The term “single chain Fv” or “scFv” as used herein refers to a polypeptide comprising a VL domain of antibody linked to a VH domain of an antibody.
Antibodies of the invention include, but are not limited to, monoclonal, multispecific, human or chimeric antibodies, single chain antibodies, Fab fragments, F(ab′) fragments, anti-idiotypic (anti-Id) antibodies (including, e.g., anti-Id antibodies to antibodies of the invention), intracellularly-made antibodies (i.e., intrabodies), and epitope-binding fragments of any of the above. The immunoglobulin molecules of the invention can be of any type (e.g., IgG, IgE, IgM, IgD, IgA and IgY), class (e.g., IgG1, IgG2, IgG3, IgG4, IgA1 and IgA2) or subclass of immunoglobulin molecule. Preferably, an antibody of the invention comprises, or alternatively consists of, a VH domain, VH CDR, VL domain, or VL CDR having an amino acid sequence of any one of the antibodies listed in Table 1, or a fragment or variant thereof. In a preferred embodiment, the immunoglobulin is an IgG1 isotype. In another preferred embodiment, the immunoglobulin is an IgG4 isotype. Immunoglobulins may have both a heavy and light chain. An array of IgG, IgE, IgM, IgD, IgA, and IgY heavy chains may be paired with a light chain of the kappa or lambda forms. Antibodies of the invention may also include multimeric forms of antibodies. For example, antibodies of the invention may take the form of antibody dimers, trimers, or higher-order multimers of monomeric immunoglobulin molecules. Dimers of whole immunoglobulin molecules or of F(ab′)2 fragments are tetravalent, whereas dimers of Fab fragments or scFv molecules are bivalent. Individual monomers withon an antibody multimer may be identical or different, i.e., they may be heteromeric or homomeric antibody multimers. For example, individual antibodies within a multimer may have the same or different binding specificities.
Multimerization of antibodies may be accomplished through natural aggregation of antibodies or through chemical or recombinant linking techniques known in the art. For example, some percentage of purified antibody preparations (e.g., purified IgG1 molecules) spontaneously form protein aggregates containing antibody homodimers, and other higher-order antibody multimers. Alternatively, antibody homodimers may be formed through chemical linkage techniques known in the art. For example, heterobifunctional crosslinking agents including, but not limited to, SMCC [succinimidyl 4-(maleimidomethyl)cyclohexane-1 carboxylate] and SATA [Nsuccinimidyl S-acethylthio-acetate] (available, for example, from Pierce Biotechnology, Inc. (Rockford, Ill.)) can be used to form antibody multimers. An exemplary protocol for the formation of antibody homodimers is given in Ghetie et al., Proceedings of the National Academy of Sciences USA (1997) 94:7509-7514, which is hereby incorporated by reference in its entirety. Antibody homodimers can be converted to Fab′2 homodimers through digestion with pepsin. Another way to form antibody homodimers is through the use of the autophilic T15 peptide described in Zhao and Kohler, The Journal of Immunology (2002) 25:396-404, which is hereby incorporated by reference in its entirety.
Alternatively, antibodies can be made to multimerize through recombinant DNA techniques. IgM and IgA naturally form antibody multimers through the interaction with the mature J chain polypeptide. Non-IgA or non-IgM molecules, such as IgG molecules, can be engineered to contain the J chain interaction domain of IgA or IgM, thereby conferring the ability to form higher order multimers on the non-IgA or non-IgM molecules. (see, for example, Chintalacharuvu et al., (2001) Clinical Immunology 101:21-31. and Frigerio et al., (2000) Plant Physiology 123:1483-94, both of which are hereby incorporated by reference in their entireties.) IgA dimers are naturally secreted into the lumen of mucosa-lined organs. This secretion is mediated through interaction of the J chain with the polymeric IgA receptor (pIgR) on epithelial cells. If secretion of an IgA form of an antibody (or of an antibody engineered to contain a J chain interaction domain) is not desired, it can be greatly reduced by expressing the antibody molecule in association with a mutant J chain that does not interact well with pIgR (Johansen et al., The Journal of Immunology (2001) 167:5185-5192 which is hereby incorporated by reference in its entirety). ScFv dimers can also be formed through recombinant techniques known in the art; an example of the construction of scFv dimers is given in Goel et al., (2000) Cancer Research 60:6964-6971 which is hereby incorporated by reference in its entirety. Antibody multimers may be purified using any suitable method known in the art, including, but not limited to, size exclusion chromatography.
Monoclonal and polyclonal context-independent ubiquitin remnant peptide antibodies have been identified. For example, the invention encompasses the monoclonal and polyclonal antibodies listed in Table 1 and the cell lines engineered to express them or capable of expressing them.
Further, the present invention encompasses the polynucleotides encoding the anti-ubiquitin remnant peptide antibodies or portions thereof. Molecules encoding e.g., VH domains, VH CDRs, VL domains, or VL CDRs having an amino acid sequence of the corresponding region of the inventive antibodies expressed by a cell that specifically bind to ubiquitin remnant peptides but not peptides having the same amino acid sequence but lacking the ubiquitin remnant, or fragments or variants thereof are also encompassed by the invention, as are nucleic acid molecules that encode these antibodies and/or molecules. In specific embodiments, the present invention encompasses antibodies, or fragments or variants thereof that bind to an epitope that comprises the ubiquitin remnant.
Methods for identifying the complementarity determining regions (CDRs) of an antibody by analyzing the amino acid sequence of the antibody are well known (see, e.g., Wu, T. T. and Kabat, E. A. (1970) J. Exp. Med. 132: 211-250; Martin et al., Methods Enzymol. 203:121-53 (1991); Morea et al., Biophys Chem. 68(1-3):9-16 (October 1997); Morea et al., J Mol. Biol. 275(2):269-94 (Jan. 1998); Chothia et al., Nature 342(6252):877-83 (December 1989); Ponomarenko and Bourne, BMC Structural Biology 7:64 (2007).
As one non-limiting example, the following method can be used to identify the CDRs of an antibody.
For the CDR-L1, the CDR-L1 is approximately 10-17 amino acid residues in length. Generally, the start is at approximately residue 24 (the residue before the 24th residue is typically a cysteine. The CDR-L1 ends on the residue before a tryptophan residue. Typically, the sequence containing the tryptophan is either Trp-Tyr-Gln, Trp-Leu-Gln Trp-Phe-Gln, or Trp-Tyr-Leu, where the last residue within the CDR-L1 domain is the residue before the TRP in all of these sequences.
For the CDR-L2, the CDR-L2 is typically seven residues in length. Generally, the start of the CDR-L2 is approximately sixteen residues after the end of CDR-L1 and typically begins on the on the residue after the sequences of Ile-Tyr, Val-Tyr, Ile-Lys, or Ile-Phe.
For the CDR-L3, the CDR-L3 is typically 7-11 amino acid residues in length. Generally, the domain starts approximately 33 residues after the end of the CDR-L2 domain. The residue before the start of the domain is often a cysteine and the domain ends on the residue before Phe in the sequence Phe-Gly-XXX-Gly (where XXX is the three letter code of any single amino acid.
For the CDR-H1, the CDR-H1 domain is typically 10-12 amino acid residues in length and often starts on approximately residue 26. The domain typically starts four or five residues after a cysteine residue, and typically ends on the residue before a Trp (the Trp is often found in one of the following sequences: Trp-Val, Trp-Ile, or Trp-Ala.
For the CDR-H2, the CDR-H2 domain is typically 16 to 19 residues in length and typically starts 15 residues after the final residue of the CDR-H1 domain. The domain typically ends on the amino acid residue before the sequence Lys/Arg-Leu/Ile/Val/Phe/Thr/Ala-Thr/Ser/Ile/Ala (which includes, for example, the sequences Lys-Leu-Thr and Arg-Ala-Ala).
For the CDR-H3, the CDR-H3 domain is typically 3-25 amino acids in length and typically starts 33 amino acid residues after the final residues of the CDR-H2 domain (which is frequently two amino acid residues after a cysteine residue, e.g., a cysteine in the sequence Cys-Ala-Arg). The domain ends on the amino acid immediately before the Trp in the sequence Trp-Gly-XXX-Gly (where XXX is the three letter code of any single amino acid).
The inventive anti-ubiquitin remnant peptide antibodies may be coupled to a detectable label such as an enzyme, a fluorescent label, a luminescent label, or a bioluminescent label. The present invention also provides anti-ubiquitin remnant peptide antibodies that are coupled to a therapeutic or cytotoxic agent. The present invention also provides anti-PA antibodies which are coupled, directly or indirectly, to a radioactive material.
In further embodiments, the anti-ubiquitin remnant peptide antibodies of the invention have a dissociation constant (KD) of 10−7 M or less for a ubiquitin remnant peptide. In preferred embodiments, the anti-ubiquitin remnant peptide antibodies of the invention have a dissociation constant (KD) of 10−9 M or less for a ubiquitin remnant peptide.
In further embodiments, antibodies of the invention have an off rate (koff) of 10−3/sec or less. In preferred embodiments, antibodies of the invention have an off rate (koff) of 10−4/sec or less. In other preferred embodiments, antibodies of the invention have an off rate (koff) of 10−5/sec or less.
The present invention also provides panels of the anti-ubiquitin remnant peptide antibodies (including molecules comprising, or alternatively consisting of, antibody fragments or variants) wherein the panel members correspond to one, two, three, four, five, ten, fifteen, twenty, or more different the anti-ubiquitin remnant peptide antibodies of the invention (e.g., whole antibodies, Fabs, F(ab′)2 fragments, Fd fragments, disulfide-linked Fvs (sdFvs), anti-idiotypic (anti-Id) antibodies, and scFvs). The present invention further provides mixtures of the anti-ubiquitin remnant peptide antibodies wherein the mixture corresponds to one, two, three, four, five, ten, fifteen, twenty, or more different the anti-ubiquitin remnant peptide antibodies of the invention (e.g., whole antibodies, Fabs, F(ab′)2 fragments, Fd fragments, disulfide-linked Fvs (sdFvs), anti-idiotypic (anti-Id) antibodies, and scFvs)). The present invention also provides for compositions comprising, or alternatively consisting of, one, two, three, four, five, ten, fifteen, twenty, or more the anti-ubiquitin remnant peptide antibodies of the present invention (including molecules comprising, or alternatively consisting of, antibody fragments or variants thereof). A composition of the invention may comprise, or alternatively consist of, one, two, three, four, five, ten, fifteen, twenty, or more amino acid sequences of one or more of the anti-ubiquitin remnant peptide antibodies or fragments or variants thereof. Alternatively, a composition of the invention may comprise, or alternatively consist of, nucleic acid molecules encoding one or more antibodies of the invention.
The present invention also provides for fusion proteins comprising an anti-ubiquitin remnant peptide antibody (including molecules comprising, or alternatively consisting of, antibody fragments or variants thereof) of the invention, and a heterologous polypeptide (i.e., a polypeptide unrelated to an antibody or antibody domain). Nucleic acid molecules encoding these fusion proteins are also encompassed by the invention. A composition of the present invention may comprise, or alternatively consist of, one, two, three, four, five, ten, fifteen, twenty or more fusion proteins of the invention.
Alternatively, a composition of the invention may comprise, or alternatively consist of, nucleic acid molecules encoding one, two, three, four, five, ten, fifteen, twenty or more fusion proteins of the invention.
The term “elution solution” refers to a solution that when brought into contact with the binding partner, results in the dissociation of the polypeptide or peptide and preferably the ubiquitin remnant peptide from the binding partner into the elution solution. Determining the salt, pH and ionic conditions necessary for such functionality is well with the ordinary skill in the art. Preferably, the elution solution is enriched for polypeptides and peptides which were bound to the binding partners relative to the polypeptides and peptides of the digest. Preferably, the elution solution has about 500 to about 5000, more preferably about 1000 to about 2000 different peptides. Most preferably, the elution solution is enriched for ubiquitin remnant peptides. Preferably, a portion of the elution solution is directly transferred to a mass spectrometer, LC-MS or LC-MS/MS. Alternatively, the elution solution is subject to further manipulation e.g., to concentrate the peptides and/or polypeptides contained therein. Mechanisms for directing solutions from liquid chromatography to mass spectrometers may be found for example in U.S. Pub. No. 20080217254.
The term “vaporizing a portion of the elution solution” means that a portion of the elution solution is preferably transferred to a mass spectrometer for vaporization and ionization.
The term “ionizing” refers to atmospheric pressure chemical ionization (APCI), chemical ionization (CI), electron impact (O), electrospray ionization (ESI), fast atom bombardment (FAB), field desorption/field ionization (FD/FI), matrix assisted laser desorption ionization (MALDI), and thermospray ionization. The preferred method of ionization is ESI as tends to minimize the propensity of macromolecules to fragment when ionized.
Preferably in ESI, liquid containing the peptides of interest is dispersed by electrospray into a fine aerosol. Preferred solvents for electrospray ionization are prepared by mixing water with volatile organic compounds (e.g. methanol, acetonitrile). To decrease the initial droplet size, compounds that increase the conductivity (e.g. acetic acid) are preferably added to the solution. Large-flow electrosprays may provide additional nebulization by an inert gas such as nitrogen. The aerosol is sampled into the first vacuum stage of a mass spectrometer through a capillary, which can be heated to aid further solvent evaporation from the charged droplets. Preferably, the solvent evaporates from a charged droplet until it becomes unstable upon reaching its Rayleigh limit. At this point, the droplet preferably deforms and emits charged jets in a process known as Rayleigh fission. During the fission, the droplet loses a small percentage of its mass along with a relatively large percentage of its charge
As used herein, “ionized molecule” refers to molecules in the elution solution that have become charged and are ready to move into the electric fields that will direct them into the mass analyzer of a mass spectrometer. Preferably, the ionized molecules include ionized polypeptides, peptides and/or ubiquitin remnant peptides present in the elution solution. Most preferably, the ionized molecules are ubiquitin remnant peptides.
The term “standard peptide” as used herein, refers to a peptide that is 1) recognized as equivalent to a peptide of interest in the digest generated by a hydrolyzing agent, e.g., the ubiquitin remnant peptide, by the appropriate binding partner; and 2) differs from the peptide of interest in a manner that can be distinguished by a mass spectrometer, e.g., by way of a mass-altering label. Preferably, the standard peptide has the same amino acid sequence as the ubiquitin remnant peptide but is synthesized utilizing elemental isotopes. Preferably, those isotopes are 15N, 13C, 18O or 2H. Alternatively, a standard peptide can 1) have the same amino acid sequence as a ubiquitin remnant peptide yet lack the ubiquitin remnant; and 2) differ from the ubiquitin remnant peptide in a manner that can be distinguished by a mass spectrometer, e.g., by lacking the ubiquitin remnant. Exemplary standard peptides are described in U.S. Pub. No. 20060154318 and 20060148093. One or more standard peptides may be added to the biological sample before or after treatment with a hydrolyzing agent such that it co-elutes with the peptide of interest into the elution solution. The standard peptide can be added directly to the elution solution.
One aspect of the invention relates to providing methods for determining a site of ubiquitination in a polypeptide. The method comprises obtaining a plurality of ubiquitinated polypeptides; digesting the ubiquitinated polypeptides with a protease, thereby generating a plurality of test peptides; enriching the plurality of test peptides for ubiquitin remnant peptides; and determining the presence of a ubiquitin remnant peptide by mass spectrometry, wherein the presence of the ubiquitin remnant peptide allows the technician to determine a site of ubiquitination of the polypeptide. The test peptide being evaluated can be ionized and/or fragmented prior to the determining step. Preferably, ionizing is performed by electrospray.
In one embodiment of this aspect of the invention, the method for determining a site of ubiquitination comprises obtaining a plurality of ubiquitinated polypeptides; digesting the ubiquitinated polypeptides with a protease; thereby generating a plurality of test peptides; at least some of which comprise a ubiquitin remnant, enriching the plurality of test peptides for ubiquitin remnant peptides; and identifying a mass difference between a test peptide and a standard peptide comprising a known identical amino acid sequence as the test peptide; the mass difference corresponding to the mass of the ubiquitin remnant, wherein detection of the mass difference indicates a site of ubiquitination in the test peptide.
In another aspect, the methods further comprise the step of mapping a sequence of a test peptide comprising a ubiquitin remnant to a polypeptide sequence comprising the same amino acid sequence as the test peptide, thereby determining the site of ubiquitination in the polypeptide sequence. In another embodiment, the ubiquitin remnant comprises GlyGly amino acid residues and has a mass of about 114 daltons. The methods can be used to detect one or more sites of ubiquitination in a polypeptide, as well as the amount of ubiquitination at particular sites in a population of polypeptides.
In a further aspect of the invention, ubiquitination sites are identified for a plurality of polypeptides in a first cell and in a second cell and the sites identified in the first cell are compared to those in the second cell. In one aspect, the first cell is a normal cell (e.g., from a healthy patient), while the second cell is from a patient with a pathological condition (e.g., a neurodegenerative disease, cancer, a disease of the immune system). Preferably, the second cell is the target of the pathology (e.g., a tumor cell from a cancer patient; a neural cell from a patient with a neurodegenerative disease). In another embodiment of this aspect of the invention, the second cell differs from the first cell in expressing one or more recombinant DNA molecules, but is otherwise genetically identical to the first cell. In a further embodiment, the site of ubiquitination is correlated with disease and detection of ubiquitination at the site is associated with risk of the disease. In another embodiment, the disease is a eurodegenerative disease, such as Alzheimer's or Pick's disease. In another aspect, the disease is cancer. In a further aspect, the disease is an abnormal immune response or inflammatory disease.
In another aspect of the invention, the methods disclosed herein are used to identify regulators of ubiquitination pathways. In one embodiment, the methods further comprise contacting a first cell with a compound and comparing ubiquitination sites identified in the first cell with ubiquitination sites in a second cell not contacted with the compound. The compound may be a therapeutic agent for treating a disease associated with an improper state of ubiquitination (e.g., abnormal sites or amounts of ubiquitination). Suitable agents include, but are not limited to, drugs, polypeptides, peptides, antibodies, nucleic acids (genes, cDNA's, RNA's, antisense molecules, siRNA/miRNA constructs, ribozymes, aptamers and the like), toxins, and combinations thereof.
Preferably, the methods further comprise generating a database comprising data files storing information relating to ubiquitination sites for a plurality of polypeptides for a plurality of different cells. Preferably, the data files also include information relating to amount of ubiquitination of a polypeptide in at least one cell. Additionally, the database comprises data relating to the source of the cell (e.g., such as a patient).
The invention further provides a computer memory comprising data files storing information relating to ubiquitination sites for a plurality of polypeptides for a plurality of different cells.
In another aspect of the invention, substantially purified test peptides, preferably ubiquitin remnant peptides, obtained after one or more separation steps are analyzed by a peptide analyzer that evaluates the mass of the peptide or a fragment thereof. Suitable peptide analyzers include, but are not limited to, a mass spectrometer, mass spectrograph, single-focusing mass spectrometer, static field mass spectrometer, dynamic field mass spectrometer, electrostatic analyzer, magnetic analyzer, quadropole analyzer, time of flight analyzer (e.g., a MALDI Quadropole time-of-flight mass spectrometer), Wien analyzer, mass resonant analyzer, double-focusing analyzer, ion cyclotron resonance analyzer, ion trap analyzer, tandem mass spectrometer, liquid secondary ionization MS, and combinations thereof in any order (e.g., as in a multi-analyzer system). Such analyzers are known in the art and are described in, for example, Mass Spectrometry for the Biological Sciences, Burlingame and Can eds., Human Press, Totowa, N.J.)
In general, any analyzer can be used that can separate matter according to its anatomic and molecular mass. Preferably, the peptide analyzer is a tandem MS system (an MS/MS system) since the speed of an MS/MS system enables rapid analysis of low femtomole levels of peptide and can be used to maximize throughput.
In a preferred embodiment of this aspect of the invention, the peptide analyzer comprises an ionizing source for generating ions of a test peptide and a detector for detecting the ions generated. The peptide analyzer further comprises a data system for analyzing mass data relating to the ions generated and for deriving mass data relating to the test peptide.
A sample comprising a test peptide can be delivered to the peptide analyzer using a delivery mechanism as described above. Interfaces between a sample source (e.g., an HPLC column) and ion source can be direct or indirect. For example, there may be an interface that provides for continuous introduction of the sample to the ion source. Alternatively, sample can be intermittently introduced to the ion source (e.g., in response to feedback from the system processor during the separation process, or while the separation system is off-line).
In another embodiment, the ion source is an electrospray which is used to provide droplets to the peptide analyzer, each droplet comprising a substantially purified test peptide obtained from previous separation step(s) (e.g., such as HPLC or reversed phase liquid chromatography). During electrospray, a high voltage is applied to a liquid stream causing large droplets to be subdivided into smaller and smaller droplets until a peptide enters the gas phase as an ion. Ionization generally is accomplished when the test peptide loses or gains a proton at one or more sites on the peptide (e.g., at the amino terminus, and/or at lysine and arginine residues). Ionization in electrospray is constant; MALDI can be used to achieve pulsed ionization. Other methods of ionization, include but are not limited to, plasma desorption ionization, thermospray ionization, and fast atom bombardment ionization as are known in the art.
When MALDI is used, peptides can be delivered to a solid support, e.g., sample plate inserted into the mass spectrometer. The support may comprise a light-absorbent matrix. In another embodiment, a substantially purified ubiquitinated polypeptide is provided on a sample plate and protease digestion occurs on the sample plate prior to ionization. For example, substantially purified ubiquitinated peptides also can be obtained from protease digests as described above and separated by a liquid chromatography method. Preferably, the peptide analyzer further comprises an ion transfer section through which ions are delivered from the ion source to the detector. The ion transfer section comprises an electric and/or magnetic field generator (e.g., an electrode ring) that modulates the acceleration of ions generated by the ionizing source. The electric/magnetic field generator directs ions through the ion transfer section of the peptide analyzer to the ion detector.
Preferably, the peptide analyzer further comprises an ion trap positioned between the ion transfer section of the analyzer and the detector, for performing one or more operations such as ion storage, ion selection and ion collision. The ion trap can be used to fragment ions produced by the ion source (e.g., causing ions to undergo collisional activated dissociation in the presence of a neutral gas ions, such as helium ions). The ion trap also can be used to store ions in stable orbits and to sequentially eject ions based on their mass-to-charge values (m/z) to the detector. An additional separation section can be provided between the ion trap and detector to separate fragments generated in the ion trap (e.g., as in tandem MS). The detector detects the signal strength of each ion (e.g., intensity), which is a reflection of the amount of protonation of the ion.
The peptide analyzer additionally preferably is associated with data system for recording and processing information collected by the detector. The data system can respond to instructions from a processor in communication with the separation system and also can provide data to the processor. Preferably, the data system includes one or more of: a computer; an analog to digital conversion module; and control devices for data acquisition, recording, storage and manipulation. More preferably, the device further comprises a mechanism for data reduction, i.e., a device to transform the initial digital or analog representation of output from the analyzer into a form that is suitable for interpretation, such as a graphical display, a table of masses, a report of abundances of ions, etc.)
The data system can perform various operations such as signal conditioning (e.g.,
providing instructions to the peptide analyzer to vary voltage, current, and other operating parameters of the peptide analyzer), signal processing, and the like. Data acquisition can be obtained in real time, e.g., at the same time mass data is being generated. However, data acquisition also can be performed after an experiment, e.g., when the mass spectrometer is off line.
The data system can be used to derive a spectrum graph in which relative intensity (i.e., reflecting the amount of protonation of the ion) is plotted against the mass to charge ratio (m/z ratio) of the ion or ion fragment. An average of peaks in a spectrum can be used to obtain the mass of the ion (e.g., peptide) (see, e.g., McLafferty and Turecek, 1993, Interpretation of Mass Spectra, University Science Books, CA).
Mass spectra can be searched against a database of reference peptides of known mass
and sequence to identify a reference peptide which matches a test peptide (e.g., comprises a mass which is smaller by the amount of mass attributable to a ubiquitin remnant). The database of standard peptides can be generated experimentally, e.g., digesting non-ubiquitinated peptides and analyzing these in the peptide analyzer. The database also can be generated after a virtual digestion process, in which the predicted mass of peptides is generated using a suite of programs such as PROWL (e.g., available from ProteoMetrics, LLC, New York; N.Y.). A number of database search programs exist which can be used to correlate mass spectra of test peptides with amino acid sequences from polypeptide and nucleotide databases, including, but not limited to: the SEQUEST program (Eng, et al., J. Am. Soc. Mass Spectrum. 5: 976-89; U.S. Pat. No. 5,538,897; Yates, Jr., III, et al., 1996, J. Anal. Chem. 68(17): 534-540A), available from Finnegan Corp., San Jose, Calif.
Data obtained from fragmented peptides can be mapped to a larger peptide or polypeptide sequence by comparing overlapping fragments. Preferably, a Ubiquitinated peptide is mapped to the larger polypeptide from which it is derived to identify the ubiquitination site on the polypeptide. Sequence data relating to the larger polypeptide can be obtained from databases known in the art, such as the nonredundant protein database compiled at the Frederick Biomedical Supercomputing Center at Frederick, Md.
In another aspect of the invention, the amount and location of ubiquitination is compared to the presence, absence and/or quantity of other types of polypeptide modifications. For example, the presence, absence, and/or quantity of phosphorylation, sulfation, glycosylation, and/or acetylation can be determined using methods routine in the art (see, e.g., Rossomando, et al., 1992, Proc. Natl. Acad. Sci. USA 89: 5779-578; Knight et al., 1993, Biochemistry 32: 2031-2035; U.S. Pat. No. 6,271,037). The amount and locations of one or more modifications can be correlated with the amount and locations of ubiquitination sites. Preferably, such a determination is made for multiple cell states.
Knowledge of ubiquitination sites can be used to identify compounds that modulate particular ubiquitinated polypeptides (either preventing or enhancing ubiquitination, as appropriate, to normalize the ubiquitination state of the polypeptide). Thus, in one aspect, the method described above may further comprise contacting a first cell with a compound and comparing ubiquitination sites/amounts identified in the first cell with ubiquitination sites/amounts in a second cell not contacted with the compound. Suitable cells that may be tested include, but are not limited to: neurons, cancer cells, immune cells (e.g., T cells), stem cells (embryonic and adult), undifferentiated cells, pluripotent cells, and the like. In one preferred aspect, patterns of ubiquitination are observed in cultured cells, such as P 19 cells, pluripotent embryonic carcinoma cells capable of differentiating into cardiac cells and skeletal myocytes upon exposure to DMSO (see Montross, et al., J. Cell Sci. 113 (Pt. 10): 1759-70).
Compounds which can be evaluated include, but are not limited to: drugs; toxins; proteins; polypeptides; peptides; amino acids; antigens; cells, cell nuclei, organelles, portions of cell membranes; viruses; receptors; modulators of receptors (e.g., agonists, antagonists, and the like); enzymes; enzyme modulators (e.g., such as inhibitors, cofactors, and the like); enzyme substrates; hormones; nucleic acids (e.g., such as oligonucleotides; polynucleotides; genes, cDNAs; RNA; antisense molecules, ribozymes, aptamers); and combinations thereof. Compounds also can be obtained from synthetic libraries from drug companies and other commercially available sources known in the art (e.g., including, but not limited to the LeadQuest® library) or can be generated through combinatorial synthesis using methods well known in the art. A compound is identified as a modulating agent if it alters the site of ubiquitination of a polypeptide and/or if it alters the amount of ubiquitination by an amount that is significantly different from the amount observed in a control cell (e.g., not treated with compound).
In further aspect of the invention, the ubiquitination states (e.g., sites and amount of ubiquitination) of first and second cells are evaluated. Preferably, the second cell differs from the first cell in expressing one or more recombinant DNA molecules, but is otherwise genetically identical to the first cell. Alternatively, or additionally, the second cell can comprise mutations or variant allelic forms of one or more genes. In one aspect,
DNA molecules encoding regulators of the ubiquitin pathway can be introduced into the second cell (e.g., E1, E2, E3, deubiquitinating proteins, fragments thereof, mutant forms thereof, variants, and modified forms thereof, or compounds identified as above) and alterations in the ubiquitination state in the second cell can be determined. DNA molecules can be introduced into the cell using methods routine in the art, including, but not limited to: transfection, transformation, electroporation, electro fusion, microinjection, and germline transfer.
The invention also provides methods for generating a database comprising data files for storing information relating to diagnostic peptide fragmentation signatures. Preferably, data in the data files include one or more peptide fragmentation signatures characteristic or diagnostic of a cell state (e.g., such as a state which is characteristic of a disease, a normal physiological response, a developmental process, exposure to a therapeutic agent, exposure to a toxic agent or a potentially toxic agent, and/or exposure to a condition). Data in the data files also preferably includes values corresponding to level of proteins corresponding to the peptide fragmentation signatures found in a particular cell state.
In one embodiment, for a cell state determined by the differential expression of at least one protein, a data file corresponding to the cell state will minimally comprise data relating to the mass spectra observed after peptide fragmentation of a standard peptide diagnostic of the protein. Preferably, the data file will include a value corresponding to
the level of the protein in a cell having the cell state. For example, a tumor cell state is associated with the overexpression of p53 (see, e.g., Kern, et al., 2001, Int. J. Oncol. 21(2): 243-9). The data file will comprise mass spectral data observed after fragmentation of a standard corresponding to a subsequence of p53. Preferably, the data file also comprises a value relating to the level of p53 in a tumor cell. The value may be expressed as a relative value (e.g., a ratio of the level of p53 in the tumor cell to the level of p53 in a normal cell) or as an absolute value (e.g., expressed in nM or as a % of total cellular proteins).
Preferably, the data files also include information relating to the presence or amount of a modified form of a target a polypeptide in at least one cell and to mass spectral data diagnostic of the modified form (i.e., peak data for a fragmented peptide internal standard which corresponds to the modified form). More preferably, the data files also comprise spectral data diagnostic of the unmodified form as well as data corresponding to the level of the unmodified form.
In one embodiment, data relating to ubiquitination sites and amounts of ubiquitination are stored in a database to create a proteome map of ubiquitinated proteins. Preferably, the database comprises a collection of data files relating to all ubiquitinated polypeptides in a particular cell type. The database preferably further comprises data relating to the origin of the cell, e.g., such as data relating to a patient from whom a cell was obtained. More preferably, the database comprises data relating to cells obtained from a plurality of patients. In one aspect, the database comprises data relating to the ubiquitination of a plurality of different cell types (e.g., cells from patients with a pathology, normal patients, cells at various stages of differentiation, and the like). In another aspect, data relating to ubiquitination patterns in cells obtained from patients with a neurological disease are stored in the database. For example, information relating to ubiquitination in cell samples from patients having any of Alzheimer's disease; amyotrophic lateral sclerosis; dementia; depression; Down's syndrome; Huntington's disease; peripheral neuropathy; multiple sclerosis; neurofibromatosis; Parkinson's disease; and schizophrenia, can be included in the database.
In a further embodiment, data relating to ubiquitination patterns in cells from patients with cancer are stored in the database, including, but not limited to patients with: adenocarcinoma; leukemia; lymphoma; melanoma; myeloma; sarcoma; teratocarcinoma; and, in particular, cancers of the adrenal gland; bladder; bone; bone marrow; brain; breast; cervix; gall bladder; ganglia; gastrointestinal; tract; heart, kidney; liver; lung; muscle; ovary; pancreas; parathyroid; prostate; salivary glands; skin; spleen; testes; thymus; thyroid; and uterus.
Additionally, data of ubiquitination patterns in cells from patients with an immune disorder may be included in the database. Such a disorder can include: acquired immunodeficiency syndrome (AIDS); Addison's disease; adult respiratory distress
syndrome; allergies; ankylosing spondylitis; amyloidosis; anemia; asthma; atherosclerosis; autoimmune hemolytic anemia; autoimmune thyroiditis; bronchitis; cholecystitis; contact dermatitis; Crohn's disease; atopic dermatitis; dermatomyositis; diabetes mellitus; emphysema; episodic lymphopenia with lymphocytotoxins; erythroblastosis fetalis; erythema nodosum; atrophic gastritis; glomerulonephritis; Goodpasture's syndrome; gout; Graves' disease; Hashimoto's thyroiditis; hypereosinophilia; irritable bowel syndrome; myasthenia gravis; myocardial or pericardial inflammation; osteoarthritis; osteoporosis; pancreatitis; polymyositis; psoriasis; Reiter's syndrome; rheumatoid arthritis; scleroderma; Sjogren's syndrome; systemic anaphylaxis; systemic lupus erythematosus; systemic sclerosis; thrombocytopenic purpura; ulcerative colitis; uveitis; Werner syndrome; and viral, bacterial, fungal, parasitic, protozoal, and helminthic infections.
Data regarding ubiquitination in apoptotic cells and in pathologies associated with the misregulation of apoptosis also can be obtained using methods according to the invention.
In a further embodiment, data regarding ubiquitination in cardiac cells and cells from patients exhibiting a cardiac disease or at risk for a cardiac disease are obtained. In one aspect, the disease is an infarction or a condition relating to ischemia. In another aspect, the disease is cardiomyopathy.
Another aspect of the invention provides for kits for detecting and/or quantifying a polypeptide modification, such as ubiquitination. In one embodiment, the kit comprises a ubiquitin remnant specific binding partner and one or more components, including, but not limited to: a protease, preferably trypsin; a ubiquitinated molecule comprising known ubiquitination sites; acetonitrile; silica resin; heptafluorobutyric acid; urea (e.g., 8M urea); a sample plate for use with a mass spectrometer; a light-absorbent matrix; an ion exchange resin; software for analyzing mass spectra (e.g., such as SEQUEST); fused silica capillary tubing; and access to a computer memory comprising data files storing information relating to ubiquitination sites for a plurality of polypeptides for a plurality of different cells. Access may be in the form of a computer readable program product comprising the memory, or in the form of a URL and/or password for accessing an internet site for connecting a user to such a memory.
Both polyclonal and monoclonal antibodies capable of recognizing the remnant of ubiquitin left from ubiquitinated proteins after digestion with the protease trypsin were generated. These antibodies were generated using a synthetic peptide library immunogen with the sequence CXXXXXXK(GG)XXXXXX, i.e., a Cysteine residue at the peptide amino-terminus, 6 “X” residues (X=any amino acid selected from all common amino acids excluding cysteine and tryptophan), a lysine residue (“K”) that has been modified by addition of a Glycine-Glycine dipeptide to the epsilon-amino group of that lysine residue and 6 more “X” residues.
Polyclonal antibodies were generated by injecting rabbits with the peptide library immunogen described above conjugated either to keyhole limpet hemocyanin (KLH) or blue carrier protein. K(GG)-specific polyclonal antibodies from 6 rabbits: BL3415, BL3416, BL4933, BL4934, BL4935, BL4936.
BL4933, BL4935 were used as starting material for monoclonal antibody development.
A monoclonal antibody from BL4933 was cloned and named recombinant antibody #3925 (D4A7A10). An additional monoclonal antibody was cloned from BL4935 (D24B6G9).
Table 1 shows the different monoclonal and polyclonal anti-ubiquitin remnant antibodies of the invention.
The heavy chain amino acid sequence of the D4A7A10 clone is provided in SEQ ID NO: 1. The light chain amino acid sequence of the D4A7A10 clone is provided in SEQ ID NO: 2. For the D4A7A10 clone (i.e., antibody #3925), using the CDR-defining rules set forth above, the CDR regions for the heavy and light chain are as follows:
The skilled artisan can readily determine the CDRs for the other antibodies disclosed herein including, without limitation, the antibody D24B6G9 cloned from BL4935.
Characterization and Screening of Ubiquitin Tag Motif Antibodies. Anti-ubiquitin remnant peptide antibodies were characterized by differential peptide ELISA against antigen peptides CXXXXXXK(GG)XXXXXX (C02-1257) and control peptides CXXXXXXKXXXXXX (173-92A). All antibodies gave strong positive signals with antigen peptides and showed no binding with control peptides. Antibodies were validated by the peptide immunoprecipitation-MS methods described below by identifying ubiquitin-modified peptides in a trypsin-digested Jurkat cell lysate: antibodies passed this validation test when their use resulted in identification of most of the seven known ubiquitination sites in ubiquitin itself. These seven sites are shown in Table 2. Note that the some of the sites are represented in more than one peptide produced by trypsin digestion due to more than one trypsin cleavage sequence near the ubiquitinated site and/or due to more than one ubiquitinatable lysine residue in the peptide. For example, the ubiquitinated site at residue 48 is found in three trypic peptides (see Table 2).
The antibodies of the invention were designed to recognize any peptide that contains ubiquitinated lysine residues regardless of surrounding peptide sequences. To illustrate the general context-independent recognition properties of one of these antibodies, the heat map shown in
Altogether 1458 non-redundant peptides were included in the frequency map shown in
Numerous experiments were performed using the isolated antibodies of the invention in the methods described in U.S. Pat. Nos. 7,198,896 and 7,300,753. Table 3 lists some of these experiments performed and the number of ubiquitinated peptides observed (both redundant and non-redundant) in each of these experiments.
The exemplary results shown below in Table 4 correspond to experiment number 3115 in Table 3. In the experiment, cellular proteins from 500 mg of mouse liver were denatured with urea, reduced with dithiothreitol, alkylated with iodoacetamide digested with the protease trypsin. The resulting peptides were separated from other cellular materials by reversed-phased solid phase extraction, then lyophilized and resuspended. Peptides containing the K(GG) modification were separated from other peptides by treatment with the immobilized polyclonal anti-ubiquitin remnant antibody BL4936. The BL4936 associated beads were washed, and bound K(GG)-peptides were eluted with dilute trifluouroacetic acid. The peptides were concentrated and then analyzed by liquid chromatography-tandem mass spectrometry LC-MS. See for example, U.S. Pat. Nos. 7,198,896 and 7,300,753, the entire disclosures of which are incorporated by reference.
This experiment resulted in the identification of 581 peptides that had been modified by ubiquitin or ubiquitin-like protein and allowed for the localization of the specific sites of ubiquitination within the predicate polypeptide. The experiment identified 6 of 7 known ubiquitination sites in ubiquitin itself. (See rows 39-48 of Table 4; Ikeda F, Dikic I. Atypical ubiquitin chains: new molecular signals. ‘Protein Modifications: beyond the Usual Suspects’ review series. EMBO Rep. 2008 June; 9(6):536-42.
Additionally, novel ubiquitination sites in enzymes responsible for linking ubiquitin to other proteins as part of the ubiquitin conjugating system were discovered (see rows 550-562 in Table 4).
Neddylation sites in ubiquitin-like molecules such as NEDD8 (see row 392 in Table 4) were also identified as trypsin digestion of neddylated proteins leaves the same K(GG) remnant as trypsin digestion of ubiquitinated proteins. Thus, the invention contemplates the use of the antibodies described herein in, for example, the methods described herein to identify neddylated proteins following digestion of such neddylated proteins with a hydrolyzing agent such as trypsin. NEDD8 is about 60% identical to ubiquitin and like ubiquitin can form polyneddylation chains (Jones J, Wu K, Yang Y, Guerrero C, Nillegoda N, Pan Z Q, Huang L. A targeted proteomic analysis of the ubiquitin-like modifier nedd8 and associated proteins. J Proteome Res. 2008 March; 7(3):1274-87). Several known ubiquitination sites in histones (e.g., H2A and H2B; see rows 13-26 and 27-30, respectfully, in Table 4) were identified. Ubiquitination of these histones is thought to regulate many nuclear processes such as transcription, silencing, and DNA repair (Weake V M, Workman J L. Histone ubiquitination: triggering gene activity. Mol. Cell. 2008 Mar. 28; 29(6):653-63).
The invention also contemplates the use of the antibodies described herein in, for example, the methods described herein to identify proteins modified by the Interferon-induced 17 kDa protein, also called the I5G15 protein because it is encoded by the I5G15 gene (see Blomstrom et al., J Biol Chem 261 (19): 8811-8816, 1986). Following digestion of such I5G15-modified proteins with a hydrolyzing agent such as trypsin, the antibodies of the invention will specifically bind to and recognize the modified lysine residues in the hydrolyzed ISG15-modified proteins (see, e.g., Zhao et al., Proc. Natl. Acad. Sci. 107(5): 2253-2258, 2010).
Unless defined otherwise, all technical and scientific terms and any acronyms used herein have the same meanings as commonly understood by one of ordinary skill in the art in the field of this invention. Although any compositions, methods, kits, and means for communicating information similar or equivalent to those described herein can be used to practice this invention, the preferred compositions, methods, kits, and means for communicating information are described herein.
All references cited above are incorporated herein by reference in their entirety to the extent allowed by law. The discussion of those references is intended merely to summarize the assertions made by their authors. No admission is made that any reference (or a portion of any reference) is relevant prior art. Applicants reserve the right to challenge the accuracy and pertinence of any cited reference.
This Application is a divisional of U.S. Ser. No. 12/967,824 filed Dec. 14, 2010, which claims benefit from U.S. provisional patent application Ser. No. 61/286,486, filed Dec. 15, 2009, the entire disclosures of which are hereby incorporated by reference. The entire disclosures of U.S. Ser. No. 11/823,775 filed Jun. 28, 2007, U.S. Ser. No. 10/777,893, filed Feb. 12, 2004, now U.S. Pat. No. 7,300,753, U.S. Ser. No. 10/175,486, filed Jun. 19, 2002, now U.S. Pat. No. 7,198,896, U.S. Ser. No. 60/299,893, filed Jun. 21, 2001, and U.S. Ser. No. 60/337,012, filed Nov. 8, 2001, are hereby incorporated by reference.
| Number | Name | Date | Kind |
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| 5538897 | Yates, III et al. | Jul 1996 | A |
| 5593844 | Carlsson et al. | Jan 1997 | A |
| 5716836 | Suiko | Feb 1998 | A |
| 5759787 | Strulovici | Jun 1998 | A |
| 5885841 | Higgs, Jr. et al. | Mar 1999 | A |
| 5932102 | Wyllie et al. | Aug 1999 | A |
| 5965352 | Stoughton et al. | Oct 1999 | A |
| 6001580 | Tani et al. | Dec 1999 | A |
| 6017693 | Yates, III et al. | Jan 2000 | A |
| 6291645 | Shin et al. | Sep 2001 | B1 |
| 6322970 | Little et al. | Nov 2001 | B1 |
| 6379970 | Liebler et al. | Apr 2002 | B1 |
| 6441140 | Comb et al. | Aug 2002 | B1 |
| 6451591 | Edwards | Sep 2002 | B1 |
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| 6818454 | Goshe et al. | Nov 2004 | B2 |
| 6982318 | Comb et al. | Jan 2006 | B1 |
| 7198896 | Rush et al. | Apr 2007 | B2 |
| 7259022 | Comb et al. | Aug 2007 | B2 |
| 7300753 | Rush et al. | Nov 2007 | B2 |
| 7344714 | Comb et al. | Mar 2008 | B2 |
| 20060148093 | Gygi et al. | Jul 2006 | A1 |
| 20080008699 | Li et al. | Jan 2008 | A1 |
| 20090022659 | Olson et al. | Jan 2009 | A1 |
| 20090317409 | Xu et al. | Dec 2009 | A1 |
| 20120149883 | Gygi et al. | Jun 2012 | A1 |
| Number | Date | Country |
|---|---|---|
| WO 9919597 | Apr 1999 | WO |
| WO 0014536 | Mar 2000 | WO |
| WO 0127624 | Apr 2001 | WO |
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| Number | Date | Country | |
|---|---|---|---|
| 20130245237 A1 | Sep 2013 | US |
| Number | Date | Country | |
|---|---|---|---|
| 61286486 | Dec 2009 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12967284 | Dec 2010 | US |
| Child | 13856933 | US |
