Patent Application
20110065148
The present invention relates to the field of carbohydrate-binding peptides, particularly monovalent carbohydrate-binding peptides. More specifically the invention relates to monovalent fucose-binding peptides. The peptides may be recombinantly produced or chemically synthesized. Preferably the peptides are derived from a lectin, in particular Aleuria aurantia lectin. Furthermore the invention relates to methods for producing the peptides, assays using the peptides for diagnosis of disorders, as well as methods using the peptides for separation and detection of fucose-containing compounds.
Lectins are a class of proteins of non-immune origin that binds carbohydrates without modifying them. They are involved in many recognition events at molecular and cellular levels. Since lectins differ in the types of carbohydrate structures they can recognize they are used to detect and separate cells, bacteria, and viruses with different carbohydrate content. Lectins are also useful tools for investigating the structure, distribution and function of different carbohydrate chains on glycoproteins and glycolipids [Liljeblad et al., 2002; Rudiger et al., 2001; Yamashita et al., 1985].
The Aleuria aurantia lectin (AAL) from the fruit bodies of Aleuria aurantia mushroom has been extensively used in structural studies of oligosaccharides. AAL is specific for L-fucose and differs from other fucose-binding lectins by having a broad specificity towards fucosylated oligosaccharides [Debray et al., 1989; Fukumori et al., 1989; Kochibe et al., 1980; Nagata et al., 1991]. AAL can bind to oligosaccharides with fucose in α1-2, α1-3, α1-4 and α1-6 linkages, with the strongest affinity towards fucose in α1-6 linkage, but is relatively insensitive to structural differences in the oligosaccharide backbone [Debray et al., 1989; Wimmerova et al., 2003]. Since AAL is one of the few fucose-binding lectins with a preferential binding to α1-6 linked fucose it has been widely used in fractionation of glycoproteins with core-fucosylated complex-type N-glycans. Since changes in fucosylation is often associated with inflammatory conditions and oncogenic transformation AAL has also been used for fractionation and analysis of disease-associated glycosylation [Rydén et al., 1999; Rydén et al., 2002; Rydén et al., 2002]. Native AAL has been shown to agglutinate human erythrocytes of both A, B and 0 subtypes [Fukumori et al., 1989]
Recombinant AAL has been produced by expression in both E. coli and Pichia Pastoris, and subsequent purification. The recombinant forms of AAL have been shown to retain their agglutinating properties [Amano et al., 2003;].
AAL is a non-glycosylated protein that has a molecular weight of 72 kDa and is composed of two identical 312 amino acid subunits [Kochibe et al., 1980]. The lectin was recently crystallized and each monomer was shown to have a six fold β-propeller structure with five binding sites for L-fucose [Fujihashi et al., 2003; Wimmerova et al., 2003]. The slight structural differences at the five binding sites as well as the results from site specific mutagenesis studies indicated that the five possible binding sites for fucose differ in affinities towards fucose [Amano et al., 2003; Fujihashi et al., 2003; Wimmerova et al., 2003]. Site 2 and 4 seems to have the highest affinity towards fucose, site 1 to have medium affinity whereas site 3 and 5 seems to bind fucose with the weakest affinity [Fujihashi et al., 2003; Wimmerova et al., 2003].
Lectin-oligosaccharide interactions are generally characterized by a weak affinity (millimolar range) for monovalent binding. This low affinity is usually compensated by the fact that most lectins are multivalent. In contrast, several bacterial and fungal lectins have been shown to display unusually high affinity towards carbohydrate ligands compared to plant or animal lectins, with Kd-values in the micromolar range [Imberty et al., 2005; Kostlanova et al., 2005; Tateno et al., 2004]. A further understanding of the binding properties of these lectins will be important for designing high-affinity carbohydrate-binding proteins.
The multivalent nature of plant lectins is important for creating high avidity binding in nature. But the fact that most lectins show variation in binding affinity and binding specificity between different binding sites in the molecule presents problems, especially when plant lectins are used for diagnostic and preparative purposes.
Several diagnostic assays have been developed which measure pathological changes in carbohydrate composition using plant lectins as reagents [Hashimoto et al., 2004; Rydén et al., 1999; Rydén et al., 2002; Rydén et al., 2002]. However, since most target glycoproteins express multimers of the carbohydrate ligand and the lectins employed are multimeric in nature, linear relationships between expressed antigen and amount of bound lectin is seldom obtained. Thus these assays are usually only diagnostically relevant in a limited part of a concentration range.
There have been few previous attempts to produce monovalent carbohydrate-binding lectins. Procedures for preparing reduced valency Concanavalin A (a mannose and glucose-binding lectin) includes chemical modification such as succinylation and/or photoaffinity labelling (Fraser et al, 1976, Beppu et al 1976, Beppu et al 1975, Tanaka et al 1981, Gunther et al 1973,). Monovalent forms of Concanavalin A have also been prepared by proteolytic digestion (Wands et al 1976,). These methods were referred to in a previous patent application (WO9855869A1). Monovalent forms of the sialic acid-binding lectins Sambucus sieboldiana and Maackia amurensis as well as the galactose-binding lectin Anthocidaris crassispina and the Gal-NAc-binding lectin Wistaria floribunda have been prepared by disulfide-bridge reduction and subsequent protection with iodoacetamide (Kaku and Shibuya 1992, Kaku et al 1993, Ozeki 1991, Kurokawa 1976). These methods are not generally applicable to other lectins, and would not work to produce monovalent binding peptides from fucose-binding lectins such as Aleuria aurantia. No prior art of producing recombinant monovalent fucose-binding lectin peptides has been found. In a study of peptides containing GlcNAc-binding hevein domains Espinosa and co-workers [Espinosa et al, 2000] used a monovalent form of wheat-germ agglutinin—the isolated B-domain (WGA-B). They found that WGA-B retained its binding capacity towards chitotriose but that the binding affinity was too low to be considered useful for practical purposes (millimolar range).
Carbohydrate-binding peptides in prior art struggle with at least three problems arising from the multivalent nature of these peptides. Firstly, the problem of agglutination when carbohydrate-binding peptides bind more than one carbohydrate-expressing entity. This is a major drawback in cell surface e analysis of carbohydrates by flow cytometry, where concentrations of lectin have to be kept below agglutinating concentration, thereby significantly hampering sensitivity of the assay. Secondly, the problem of not achieving a linear relationship between carbohydrate expression and lectin-binding in more than just a limited part of a concentration range in an assay. Thirdly, the individual binding sites in multimeric lectins such as Aleuria aurantia differ in binding affinity and specificity towards carbohydrate ligands, which makes them unreliable for diagnostic purposes.
The present invention meets at least partly needs of prior art by providing isolated monovalent fucose-binding peptides, methods for productions thereof, assays using the peptides for diagnosis of disorders, as well as methods using the peptides for separation and detection of fucose-containing compounds. The peptides of the invention prevent agglutination and simultanously show reasonable binding affinities (micromolar range). Furthermore the peptides enable linear relationships between carbohydrate expression and lectin binding, thus enhancing the diagnostic range of an assay and the further applicability in biotechnological fields. Furthermore the peptides show a narrower specificity range than the native lecin.
In a first aspect the present invention relates to isolated monovalent fucose-binding peptides. In preferred embodiments the peptides are derived from lectin or show at least 80% homology to a lectin.
In one embodiment the peptides are derived from Aleuria aurantia lectin. In another embodiment the peptides comprise amino acid sequences showing at least 80% homology to the Aleuria aurantia lectin domains Mono-F1 (SEQ ID NO: 2), Mono-F2 (SEQ ID NO: 4), Mono-F3 (SEQ ID NO: 6), Mono-F4 (SEQ ID NO: 8) and Mono-F5 (SEQ ID NO: 10), respectively, particularly the Mono-F2 domain.
The invention further provides nucleic acid molecules coding for peptides of the invention, vectors comprising the nucleic acid molecules and host cells comprising the vectors. The nucleic acid sequences encoding Mono-F1, Mono-F2, Mono-F3, Mono-F4 and Mono-F5 are given as SEQ ID NOs: 1, 3, 5, 7 and 9, respectively, in the appended sequence listing.
In another aspect the invention relates to methods for producing peptides according to the invention, in which above-mentioned host cells are cultivated and peptides isolated.
Furthermore the invention relates to assays for the diagnosis of disorders as well as to methods for separation and detection of fucose-containing compounds.
With “AAL” is meant Aleuria aurantia lectin, i.e. lectin derived from the Aleuria aurantia mushroom.
With “fucose-containing compounds” is meant fucose or any free oligosaccharide or oligosaccharide conjugated or bound to an aglycon such as polypeptide, lipid, biomolecule or mechanical support, containing one or more fucose residues.
With “ability to bind fucose and/or fucose containing compounds” is meant an ability to bind with a binding affinity with Kd of less than 100 μM, if not otherwise specified.
By “peptides having X % identity to a sequence” is meant peptides, in which one or more amino acid residues have been added, deleted, replaced, or chemically modified, but where at least X % of the amino acids are the same as in the specified amino acid sequence. Algorithms for computing such percentages of identity are known in the art, e.g. CLUSTAL W.
The term “comprising” shall be construed as open, i.e. an entity comprising a certain matter may also contain further matter.
The term “consisting” shall be construed as closed, i.e. an entity consisting of certain matter does not include any further matter.
For the purposes of this disclosure, the definition of an entity as comprising certain subject matter shall be construed as including the specific case of the same entity consisting of said subject matter.
Drawing 1—Amino acid sequence of Mono-F2.
Amino acids 1-16 (italic) correspond to his-tag and thrombin recognition site.
Amino acids 17-127 (bold) correspond to AAL sequence (aa 51-161)
Arrow indicate thrombin cleavage site. The calculated molecular weight of Mono-F2 is 14037 Da. The calculated molecular weight of Mono-F2 without the His-tag is 12141 Da.
Drawing 2—Nucleotide sequence of Mono-F2.
Sequence in italic corresponds to start codon (ATG) and sequence coding for his-tag and thrombin recognition site. Bold sequence corresponds to sequence encoding Ser51 to Gly 161 in native AAL
Drawing 3—SDS-PAGE analysis of purified Mono-F2
Drawing 4—Oligosaccharide affinity analysis of Mono-F2 using surface plasmon resonance analysis (BIACORE).
FIG. A shows sensorgrams for binding of a glycopeptide carrying one B-tri epitope (B-tri-KE2) to immobilized Mono-F2. The sensorgrams were obtained by injection of B-tri KE2 in concentrations of (from bottom to top curve) 0.05, 0.1, 1, 2, 5, 10, 25, 50, 75, and 100 μM. FIG. B shows the steady state analysis of the interaction of B-tri KE2 with sensor-bound Mono-F2. ΔRU values determined from the steady state plateau region were plotted as a function of analyte concentration, and the data was fitted by nonlinear regression according to a single site Langmuir binding model. The obtained Kd-value for the interaction was 31 μM.
Drawing 5—chromatograms of some fucosylated human milk oligosaccharides (LNnF I, LNF II and LNF III) and a non-fucosylated control (LNT) on a silica column with immobilized Mono-F2.
Drawing 6—Table showing oligosaccharide structures
Drawing 7—Differences in specificity of binding between Mono-F2 and recombinant full length AAL.
ELISA showing binding of Mono-F2 and recombinant AAL (rAAL) to oligosaccharide glycoconjugates.
Drawing 8—Similar binding of Mono-F2 with and without His-tag in binding to fucosylated oligosaccharides.
ELISA showing binding of Mono-F2 with (MonoF2) or without (MonoF2-T) His-tag to oligosaccharide glycoconjugates.
Using a small monovalent carbohydrate-binding peptide would set aside the agglutination tendency and enable linear relationships between carbohydrate expression and lectin binding, thus enhancing the diagnostic range of an assay. Monovalent carbohydrate-binding peptides with reasonable binding affinities (less than 100 μM) would consequently provide important reagents that could be valuable for diagnostic and therapeutic purposes as well as in biotechnological applications. However, previous attempts to use monovalent carbohydrate-binding peptides have failed due to low binding affinities of these peptides.
Thus, in a first aspect the present invention provides isolated monovalent fucose-binding peptides. In one embodiment the peptides are derived from lectins.
Crystallization analysis has shown that AAL forms dimers of two structurally identical subunits. The three-dimensional structure of each subunit is arranged as six “blades” of four-stranded anti-parallel β-sheet structural elements in a cylindrical arrangement. A so called “six-bladed β-propeller fold”. The fucose binding sites are located between two consecutive blades as pockets at the external face of the cylinder. Since the overall three-dimensional structure of the five fucose binding sites are similar, it should be possible to construct monovalent fucose-binding peptides corresponding to all five individual binding sites in AAL.
Since it is likely that the different binding sites differ in terms of binding specificity and affinity, the use of monovalent fucose-binding peptides will provide more specific reagents for diagnostic and separation purposes.
In another embodiment the invention relates to isolated monovalent fucose-binding peptides derived from Aleuria aurantia lectin (AAL), in particular peptides comprising an amino acid sequence of any of the AAL fucose-binding sites Mono-F1 (SEQ ID NO: 2), Mono-F2 (SEQ ID NO: 4), Mono-F3 (SEQ ID NO: 6), Mono-F4 (SEQ ID NO: 8) and Mono-F5 (SEQ ID NO: 10), respectively.
In still another embodiment the invention relates to a peptide comprising the site 2 of AAL (Mono-F2) or a peptide showing at least 80% homology thereto. It was found that this monovalent peptide retains the ability to bind fucosylated oligosaccharides with micromolar affinities. Furthermore the Mono-F2 site preferentially binds fucose linked α1-2 as opposed to the native AAL molecule that preferentially bind fucose linked α1-6.
It is envisioned that the peptides derived from naturally occurring lectins, such as AAL, may retain some or all of their fucose-binding ability also if some amino acid residues in the peptides are deleted or changed, or if further amino acid residues are inserted or added. The invention includes all such variants, and especially such variants the amino acid sequence of which retain a certain percentage of identity to the amino acid sequence of the naturally occurring lectin sequence, such as 80%, 85%, 90%, 95% or 98%.
Furthermore the peptide of the invention has a binding affinity for fucose with a Kd value of less than 100 μM, more preferably less than 50 μM and most preferred less than 10 μM.
In still another embodiment the invention is related to monovalent fucose-binding peptides for purification, separation and detection, wherein the peptides are conjugated or fused with tags. Tags may be conjugated or fused with peptides of the invention by way of recombinant or chemical procedures, as is known to the skilled person in the art. By tags meaning a peptide such as poly-histidine, FLAG or Myc or a biomolecule such as biotin, with high affinity (Kd less than 10−7 M) to its ligand. The tag is used in purification of lectin from cell culture using affinity chromatography where the affinity support is conjugated with the tag ligand. This purification procedure renders possible purification of lectin without addition of free fucose to the elution buffers, which may otherways affect lectin properties.
In still another aspect the invention provides nucleic acid sequences coding for the peptides of the invention.
In another aspect the invention relates to recombinant expression vectors comprising the above nucleic acid sequences. Such recombinant vectors may be one capable of being expressed in eukaryotic and prokaryotic hosts. The vector containing, in addition to the above nucleic acid sequences, other sequences such as sequences that are known for expression of the desired sequence and the maintenance and propagation of the vector in the host cell. Constructions of such vectors are known to the skilled person in the art.
In yet another aspect the invention provides host cells comprising the above vectors, the host cells being a mammalian cell, a bacterium, a fungal cell, a yeast cell or an insect cell.
In a further aspect the invention relates to methods for producing the peptides of the invention, comprising the steps of:
In particular, the invention relates to methods for recombinant production of peptides homologous to the AAL sequence that comprises two consecutive blades with one fucose-binding site in-between, preferably the Mono-F2 site.
A person skilled in the art is familiar with the appropriate conditions for culturing the host cells and isolating the peptides. The peptide can be collected from the host cell medium. On the other hand the peptide can also remain in the host cell and can be isolated from there. When E. coli are transformed with a vector encoding Mono-F2, the resulting Mono-F2 peptide is present both in soluble form and as insoluble protein aggregates (inclusion bodies). Thus, there are two methods for isolating peptides of the invention from transformed E. coli. Soluble peptides of the invention are obtained after sonication of transformed E. coli. After centrifugation the supernatant is applied to an affinity column preferentially consisting of a matrix with immobilized ligands towards fused tags on the peptide of the invention.
In order to isolate peptides from inclusion bodies the sediment of E. coli sonicate is dissolved under reducing and denaturing conditions after removal of soluble proteins. The denatured protein solution is applied to an affinity column. Renaturation is carried out by dilution of the denaturing buffer. Active carbohydrate binding peptide is obtained after elution from the affinity column.
The invention also relates to methods for separation and detection of fucose-containing compounds for diagnostic procedures using a peptide of the invention and/or a chimeric molecule or complex comprising said peptide, as a reagent in diagnostic assays for analysis of disease-associated changes in fucosylation of oligosaccharides on glycosylated proteins in humans or animals.
In one aspect the invention relates to methods for detecting a fucose-containing compound in a sample, comprising the steps of:
Oligosaccharides are detected by its content of fucose. Altered fucose levels may be seen—as a marker for disease—in a number of pathological processes such as inflammation, infectious disease recognition and neoplastic progression (Listinsky et al 1998)
We have previously shown that fucosylation of the acute phase protein al-acid glycoprotein is elevated as a consequence of pathological conditions such as chronic inflammatory disease and liver disease. We developed a lectin-based immunoassay for specific measurement of AGP fucosylation. The assay was based on quantization of the number of fucose residues on AGP isolated from patient serum using AAL. Using this assay we could show that elevated AGP fucosylation was a marker for inflammation status in rheumatic patients and furthermore useful for diagnosis of liver fibrosis and cirrhosis. The peptides of the invention would have the potential to further increase specificity and diagnostic detection range of these types of glycodiagnostic assays.
Thus, in one aspect the invention provides an assay for the diagnosis of disorders, such as liver fibrosis, cirrhosis, inflammatory diseases and cancer, comprising the steps of
In one application of the invention antibodies directed against AGP are coated in wells of a polystyrene microtiter plate. Diluted serum or plasma are added to the wells and AGP is captured on the antibodies in the wells. After washing, the peptide of the invention covalently conjugated with a tag for detection such as biotin is added to the wells. After additional washing horse-radish peroxidase (HRP) labeled streptavidin are added. HRP will catalyze the conversion of a substrate to a colored substance and the amount of color in the wells is proportional to the fucose level on AGP (Rydén et al 1999).
The invention also relates to the use of the peptides of the invention for separation and detection of fucose-containing compounds in laboratory or industrial use. The separation and detection procedures may be used for purification of fucose-containing compounds.
In another aspect the invention provides a method for separation of fucose-containing compounds from other compounds comprising the steps of
The invention will now be described by way of the following non-limiting examples and accompanying drawings.
A pET-28b-plasmid containing cDNA encoding full length His-tagged AAL was obtained as described (Olausson et al. 2008). A pET-28b-plasmid containing cDNA encoding Mono-F2 (SEQ ID NO: 4) was obtained by
1. Insertion of a NdeI restriction enzyme cleavage site at nucleotide position 150 in the AAL coding sequence
2. Insertion of a stop codon site at nucleotide position 480 in the AAL coding sequence to remove the 3′ segment of AAL corresponding to nucleotides 481-939.
3. Restriction enzyme cleavage of the plasmid with NdeI to remove the 5′ segment of AAL corresponding to nucleotides 1-150.
4. Ligation of the plasmid using T4 ligase.
The amino acid sequence of the His-tagged form of Mono-F2 and its corresponding cDNA sequence are shown in Drawing 1 and Drawing 2. The cDNA sequence was confirmed by Sanger dideoxy sequencing.
Site specific mutagenesis was performed using QuickChange Multi Site-Directed Mutagenesis kit from Stratagene (La Jolla, Calif.). The primers used are shown below.
The resulting plasmid was transformed into the E. coli strain BL21/DE3 (Invitrogen). BL21/DE3 harbouring the recombinant pET-28b-Mono-F2 plasmid was added to 500 mL of LB-medium containing 30 μg/mL kanamycin and incubated at 37° C. with shaking until OD600 was between 0.6-0.9. To induce the synthesis of Mono-F2, isopropyl-beta-D-thiogalactopyranoside (IPGT) was added to a final concentration of 0.5 mM and the cells were incubated at room temperature over night with shaking. Cells were collected by centrifugation and sonicated for 4×30 seconds in 10 mM phosphate buffer saline, pH 7.2 (PBS). The sonicate was centrifuged first at 3200 g for 20 minutes then at 19000 g for 15 minutes both at 4° C. to remove debris. The supernatant containing Mono-F2 was purified by affinity chromatography using a 1 mL Ni-column (HiTrap™ Chelating HP column, Amersham Biosciences, Uppsala, Sweden) at a flow rate of 1 mL/min.
Purified Mono-F2 was analyzed by SDS-PAGE and migrated as a single band with a molecular weight of approximately 14 kDa. The result is shown in Drawing 3.
The hemagglutination activity of full length rAAL and Mono-F2 was determined by serial dilutions of the lectins in PBS and mixing with an equal volume (50 μL) of 2% human type 0 erythrocytes suspended in PBS. After incubation at room temperature for 1 h the minimum lectin concentration that gave a positive reaction was determined. The minimal concentration of rAAL to produce hemagglutination was 2.5 μg/ml (˜71 nM) whereas Mono-F2 did not give hemagglutination even in concentrations up to 200 μg/ml (˜14000 nM).
Purified Mono-F2 was analyzed on a 1 mL fucose-agarose column (Sigma-Aldrich, Stockholm, Sweden). The column was equilibrated with 20 mL PBS. Mono-F2 was added and the column was incubated for 20 minutes at 4° C. with gentle rocking. After incubation the column was washed with PBS until the absorbance at 280 nm had reached zero. Elution was performed with 4 mL of 0.15 M L-fucose in PBS, 4 mL of 1 M L-fucose in PBS, and lastly with glycine buffer pH 2.5. Fractions (1 mL) were collected with monitoring of absorbance at 280 nm. The fractions were further analysed by SDS-PAGE. The analysis showed that Mono-F2 could not be eluted with 0.15 M fucose. Very little was eluted with 1 M fucose. A low-pH buffer had to be used to get full elution of Mono-F2 from the fucose-agarose column indicating high affinity binding to fucose.
Surface Plasmon resonance (SPR) measurements were performed using a Biacore 2000 (BiacoreAB, Uppsala, Sweden) at 25° C. with PBS as running buffer and a flow rate of 5 μL/min. Channel two contained Mono-F2 (6748 RU) whereas channel one was used as the control flow cell. A research grade CM5 sensor chip was activated with a 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide/Nhydroxysuccinimide solution for 7 min. Then 10 μL, of 1.1 μM Mono-F2 in acetate buffer (pH 5.0) was injected into flow cell two. The unreacted species on the sensor surface were blocked by a 35 μL, injection of 1 M ethanolamine. The blank channel was treated identically except for the lectin injection. Then 30 μL, of carbohydrate or glycopeptide solutions (concentrations between 0.001 and 150 μM) in running buffer were injected into the flow cells using the kinject mode. The equilibrium response (after subtraction from the response of the reference surface) of each experiment was used to create curves of analyte binding, which were fitted to a 1:1 steady-state affinity model using Scrubber version 2.0 software (BioLogic Software Pty Ltd, Campbell, Australia). When using a synthesized glycopeptide glycosylated in a single site with the B-tri oligosaccharide (Fucα1-2[Galα1-3]Galβ1-) the sensorgrams obtained revealed an affinity (Kd) of Mono-F2 towards the fucosylated oligosaccharide of 16 μM. The results are shown in Drawing 4.
Mono-F2 was immobilized on silica particles (5 μM, 300 Å) and packed in an affinity column (50×0.32 mm) and chromatography of a number of oligosaccharides were examined. LNF I, LNF II and LNF III was retarded on the column with increasing retention times whereas LNT (non fucosylated) was not bound to the column. The results are shown in Drawing 5. Elutions of oligosaccharides were detected by UV absorbance at 210 nm.
Purified Mono-F2 and full length rAAL were biotinylated using IMMUNOPROBE™ Biotinylation Kit (Sigma-Aldrich, Stockholm, Sweden) according to the manufacturer's instruction. The biotin/protein ratio was determined to 1.1 biotin moieties per protein molecule for both Mono-F2 and rAAL. Microtiter plates (Nunc MaxiSorp™ eBioscience, San Diego, Calif.) were coated with 0.2 μg of LNnF I-BSA, LNF II-BSA, LNF III-HSA, LNT-BSA; 0.1 μg of B-tri-HSA, SLex-HSA and SLea-HSA in 100 μL coating buffer (15 mM Na2CO3, mM NaHCO3, 0.02% NaN3, pH 9.6). Then 100 μL of biotinylated Mono-F2 or full length rAAL was added to the wells. After addition of ExtrAvidin (E-2632 Sigma-Aldrich, Stockholm, Sweden) and phosphatase substrate (Sigma 104®, Sigma-Aldrich, Stockholm, Sweden) the amount of Mono-F2 or full length AAL binding to each well were measured at 405 nm using a VERSAmax microplate reader (Molecular Devices Corporation, Sunnyvale, Calif.).
Structures of the analyzed oligosaccharides are depicted in Drawing 6.
Both rAAL and Mono-F2 showed only low background binding to the non-fucosylated oligosaccharide LNT. rAAL bound to all fucosylated oligosaccharides in the ELISA assay, whereas Mono-F2 showed a much more restricted binding specificity binding only non-sialylated oligosaccharide structures with α1-2 or α1-4 linked fucose (Drawing 7).
This may make it suitable for detecting disease-related changes such as hyper-fucosylation of glycoproteins in liver disease, and cancer.
To analyze whether the His-tag on Mono-F2 affected the fucose binding the ELISA analysis was also performed using Mono-F2 pre-treated with thrombin protease to remove the His-tag. Biotin labelled Mono-F2 (50 μg) in PBS was incubated with 2 units of thrombin protease (Amersham Biosciences, Uppsala, Sweden) for 2 hours at room temperature. SDS-PAGE analysis of Mono-F2 after thrombin treatment showed a single band with a molecular weight about 2000 Da lower than for non treated rAAL confirming complete cleavage of the His-tag. ELISA analysis using the thrombin treated Mono-F2 (Mono-F2-T) showed identical binding as non-treated Mono-F2 to LNnF I-, LNF II- and LNF III-BSA conjugates indicating that the His-tag does not contribute to the binding of fucosylated oligosaccharides (Drawing 8).
A pET-28b-plasmid containing cDNA encoding Mono-F4 (SEQ ID NO: 8) was obtained exactly as for Mono-F2 (Example 1). Except that the primers used were the following:
| Number | Date | Country | Kind |
|---|---|---|---|
| 0801032-4 | May 2008 | SE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2009/050505 | 5/8/2009 | WO | 00 | 11/8/2010 |
