The Influence of an Intramolecular Hydrogen Bond in Differential Recognition of Inhibitory Acceptor Analogs by Human ABO(H) Blood Group A and B Glycosyltransferases

Human ABO(H) blood group glycosyltransferases GTA and GTB catalyze the final monosaccharide addition in the biosynthesis of the human A and B blood group antigens. GTA and GTB utilize a common acceptor, the H antigen disaccharide α-l-Fucp-(1→2)-β-d-Galp-OR, but different donors, where GTA transfers GalNAc from UDP-GalNAc and GTB transfers Gal from UDP-Gal. GTA and GTB are two of the most homologous enzymes known to transfer different donors and differ in only 4 amino acid residues, but one in particular (Leu/Met-266) has been shown to dominate the selection between donor sugars. The structures of the A and B glycosyltransferases have been determined to high resolution in complex with two inhibitory acceptor analogs α-l-Fucp(1→2)-β-d-(3-deoxy)-Galp-OR and α-l-Fucp-(1→2)-β-d-(3-amino)-Galp-OR, in which the 3-hydroxyl moiety of the Gal ring has been replaced by hydrogen or an amino group, respectively. Remarkably, although the 3-deoxy inhibitor occupies the same conformation and position observed for the native H antigen in GTA and GTB, the 3-amino analog is recognized differently by the two enzymes. The 3-amino substitution introduces a novel intramolecular hydrogen bond between O2′ on Fuc and N3′ on Gal, which alters the minimum-energy conformation of the inhibitor. In the absence of UDP, the 3-amino analog can be accommodated by either GTA or GTB with the l-Fuc residue partially occupying the vacant UDP binding site. However, in the presence of UDP, the analog is forced to abandon the intramolecular hydrogen bond, and the l-Fuc residue is shifted to a less ordered conformation. Further, the residue Leu/Met-266 that was thought important only in distinguishing between donor substrates is observed to interact differently with the 3-amino acceptor analog in GTA and GTB. These observations explain why the 3-deoxy analog acts as a competitive inhibitor of the glycosyltransferase reaction, whereas the 3-amino analog displays complex modes of inhibition. Human ABO(H) blood group glycosyltransferases GTA and GTB catalyze the final monosaccharide addition in the biosynthesis of the human A and B blood group antigens. GTA and GTB utilize a common acceptor, the H antigen disaccharide α-l-Fucp-(1→2)-β-d-Galp-OR, but different donors, where GTA transfers GalNAc from UDP-GalNAc and GTB transfers Gal from UDP-Gal. GTA and GTB are two of the most homologous enzymes known to transfer different donors and differ in only 4 amino acid residues, but one in particular (Leu/Met-266) has been shown to dominate the selection between donor sugars. The structures of the A and B glycosyltransferases have been determined to high resolution in complex with two inhibitory acceptor analogs α-l-Fucp(1→2)-β-d-(3-deoxy)-Galp-OR and α-l-Fucp-(1→2)-β-d-(3-amino)-Galp-OR, in which the 3-hydroxyl moiety of the Gal ring has been replaced by hydrogen or an amino group, respectively. Remarkably, although the 3-deoxy inhibitor occupies the same conformation and position observed for the native H antigen in GTA and GTB, the 3-amino analog is recognized differently by the two enzymes. The 3-amino substitution introduces a novel intramolecular hydrogen bond between O2′ on Fuc and N3′ on Gal, which alters the minimum-energy conformation of the inhibitor. In the absence of UDP, the 3-amino analog can be accommodated by either GTA or GTB with the l-Fuc residue partially occupying the vacant UDP binding site. However, in the presence of UDP, the analog is forced to abandon the intramolecular hydrogen bond, and the l-Fuc residue is shifted to a less ordered conformation. Further, the residue Leu/Met-266 that was thought important only in distinguishing between donor substrates is observed to interact differently with the 3-amino acceptor analog in GTA and GTB. These observations explain why the 3-deoxy analog acts as a competitive inhibitor of the glycosyltransferase reaction, whereas the 3-amino analog displays complex modes of inhibition. The human blood group A and B oligosaccharide antigens are respectively formed by the transfer of GalNAc by glycosyltransferase GTA 1The abbreviations used are: GTAhuman ABO(H) blood group glycosyltransferase AGTBhuman ABO(H) blood group glycosyltransferase BCNScrystallography NMR softwareADA bufferN-[2-acetamido]-2-iminodiacetic acidFucL-fucoseGald-galactose.1The abbreviations used are: GTAhuman ABO(H) blood group glycosyltransferase AGTBhuman ABO(H) blood group glycosyltransferase BCNScrystallography NMR softwareADA bufferN-[2-acetamido]-2-iminodiacetic acidFucL-fucoseGald-galactose. or Gal by glycosyltransferase GTB to the common H-disaccharide α-l-Fucp-(1→2)-β-d-Galp-OR, where R is a glycoprotein or glycolipid (1.Watkins W.M. Harris H. Hirschhorn K. Advances in Human Genetics. Vol. 10. Plenum Publishing Corp., New York1980: 1-136Google Scholar). Generally, humans with the gene for GTA have blood group A, those with GTB have blood group B, those with both genes have blood group AB, and those with neither have blood group O. Glycosyltransferases in general have been implicated as indicators of cancer progression, susceptibility to infectious diseases, glycoprotein activity, and heart and autoimmune diseases (for review, see Ref. 2.Greenwell P. Glycoconj J. 1997; 14: 159-173Crossref PubMed Scopus (131) Google Scholar), and the human ABO(H) blood group glycosyltransferases in particular are viewed as a model system for the study of action and specificity of this class of enzyme. human ABO(H) blood group glycosyltransferase A human ABO(H) blood group glycosyltransferase B crystallography NMR software N-[2-acetamido]-2-iminodiacetic acid L-fucose d-galactose. human ABO(H) blood group glycosyltransferase A human ABO(H) blood group glycosyltransferase B crystallography NMR software N-[2-acetamido]-2-iminodiacetic acid L-fucose d-galactose. When the primary structures of GTA and GTB were determined, it was found that they differ in only four amino acid residues which, given that they share a common acceptor, were assumed to confer their ability to distinguish between the donor substrate molecules (3.Yamamoto F. Clausen H. White T. Marken J. Hakomori S. Nature. 1990; 345: 229-233Crossref PubMed Scopus (890) Google Scholar). X-ray crystallographic studies of the catalytic domains of the two enzymes revealed that their structures are almost identical outside of these four residues, that only two of these four residues served to distinguish between donor substrates, and that the acceptor substrate binding sites were nearly superimposable (4.Patenaude S.I. Seto N.O. Borisova S.N. Szpacenko A. Marcus S.L. Palcic M.M. Evans S.V. Nat. Struct. Biol. 2002; 9: 685-690Crossref PubMed Scopus (201) Google Scholar). To assist in further elucidating the mechanisms of these glycosyltransferases, specific analogs of the acceptor molecules were made and characterized kinetically by their ability to inhibit the enzyme reaction. The targeting of the acceptor moiety at the 3-OH linkage site (the point at which the monosaccharide is transferred to the acceptor) of the Gal ring via modification to 3-deoxy and 3-amino analogs (5.Lowary T.L. Hindsgaul O. Carbohydr. Res. 1993; 249: 163-195Crossref PubMed Scopus (61) Google Scholar, 6.Lowary T.L. Hindsgaul O. Carbohydr. Res. 1994; 251: 33-67Crossref PubMed Scopus (91) Google Scholar) produced potent inhibitors of glycosyltransferase activity (Fig. 1). The 3-deoxy analog was found to be a competitive inhibitor of both GTA and GTB, with Ki ranging from 14 to 68 μm, and was shown to inhibit GTA in cell culture such that the expression of surface A antigen was significantly reduced (7.Laferte S. Chan N.W. Sujino K. Lowary T.L. Palcic M.M. Eur. J. Biochem. 2000; 267: 4840-4849Crossref PubMed Scopus (25) Google Scholar). The Ki of the 3-amino analog could not be determined, as the mode of inhibition for both GTA and GTB was observed not to fit standard models of inhibition. However, it was estimated that Ki for the 3-amino analog is in the 200-nm range for GTA (5.Lowary T.L. Hindsgaul O. Carbohydr. Res. 1993; 249: 163-195Crossref PubMed Scopus (61) Google Scholar, 6.Lowary T.L. Hindsgaul O. Carbohydr. Res. 1994; 251: 33-67Crossref PubMed Scopus (91) Google Scholar). To understand the different behaviors of the two inhibitors and, specifically, the mode of binding of the 3-amino analog, we determined structures of both GTA and GTB in complex with the 3-deoxy and 3-amino analogs both in the absence and presence of UDP. Protein Production—Protein production was carried out as described in Ref. 8.Marcus S.L. Polakowski R. Seto N.O. Leinala E. Borisova S. Blancher A. Roubinet F. Evans S.V. Palcic M.M. J. Biol. Chem. 2003; 278: 12403-12405Abstract Full Text Full Text PDF PubMed Scopus (87) Google Scholar. Inhibitor Synthesis—Acceptor analogs were synthesized as reported previously (5.Lowary T.L. Hindsgaul O. Carbohydr. Res. 1993; 249: 163-195Crossref PubMed Scopus (61) Google Scholar, 6.Lowary T.L. Hindsgaul O. Carbohydr. Res. 1994; 251: 33-67Crossref PubMed Scopus (91) Google Scholar) except for the coupling reaction to produce the protected 3-deoxydisaccharide. For this step, octyl 4,6-O-benzylidene-3-deoxy-β-d-xylo-hexopyranoside (61 mg, 16.7 mmol) and phenyl-2,3,4-tri-O-benzyl-1-thio-β-l-fucopyranoside (105 mg, 20 mmol) were dissolved in dry CH2Cl2/ether (6 ml, ratio of 1/5, v/v) at room temperature and cooled to 0 °C. Then N-iodosuccinimide (45 mg, 20 mmol) and a catalytic amount of trifluoromethanesulfonic acid were added, and the mixture was stirred for 3 h. The reaction was quenched by the addition of Et3N. The mixture was diluted with CH2Cl2 (20 ml) and washed with saturated Na2SO3 (2 × 10 ml), water, and brine. The organic phase was dried over anhydrous Na2SO4. Removal of the solvent followed by chromatography on silica gel (6:1, hexane:ethyl acetate) gave the desired 3-deoxydisaccharide as a white solid (96 mg, 74%), which was hydrogenated as originally described. Protein Crystallization—Crystals of native GTA and GTB were grown as reported previously (4.Patenaude S.I. Seto N.O. Borisova S.N. Szpacenko A. Marcus S.L. Palcic M.M. Evans S.V. Nat. Struct. Biol. 2002; 9: 685-690Crossref PubMed Scopus (201) Google Scholar). Crystals were soaked with various combinations of UDP-GalNAc, UDP-Gal, UDP, and acceptor analogs. Soaking solution contained 7.5% polyethylene glycol 4000 (Sigma), 15% glycerol (BDH), 75 mm ADA buffer (Sigma), pH 7.5, 10 mm MnCl2 (Fisher), and 10 mm acceptor for 3–4 days. UDP, UDP-GalNAc, or UDP-Gal (Sigma) was added to the soaking solution at a concentration of 10–15 mm for 20–25 h. At the end of the soaking period, crystals were frozen in liquid propane using magnetic crystal caps (Hampton Research), and the caps were stored in liquid nitrogen for transport to the beamline. Data Collection and Structure Determination—Data was collected at beamline X8C at the National Synchrotron Light Source at Brookhaven National Laboratories at a wavelength of 1.15 Å. Two data sets (GTA+DI and GTA+AI) were collected on a MAR 300 mounted on a Rigaku RU300 generator at Queen's University (Kingston, Ontario, Canada). All data were collected at low temperature using a Cryostream 600 cooler. Data was reduced and scaled with HKL2000 software (9.Otwinowski Z. Minor W. Methods Enzymol. 1997; 276: 307-326Crossref PubMed Scopus (38526) Google Scholar). Initial rigid body refinement in CNS (10.Brunger A.T. Adams P.D. Clore G.M. DeLano W.L. Gros P. GrosseKunstleve R.W. Jiang J.S. Kuszewski J. Nilges M. Pannu N.S. Read R.J. Rice L.M. Simonson T. Warren G.L. Acta Crystallogr. Sec. D. 1998; 54 (Pt. 5): 905-921Crossref PubMed Scopus (16957) Google Scholar) was carried out by using the native GTA and GTB structures with and without H-antigen and UDP bound (PDB codes 1LZ0, 1LZ7, 1LZI, and 1LZJ). This procedure was followed by overall structural refinement using CNS. Leastsquared overlaps of structures were calculated by using LSQKAB within the CCP4 program suite (11.Collaborative Computational Project Number 4 Acta Crystallogr. Sec. D. 1994; 50: 760-763Crossref PubMed Scopus (19748) Google Scholar). All overlaps shown are based on protein-protein overlaps to the GTB structure (PDB code 1LZJ). Diagrams were made using ChemSketch and SETOR (12.Evans S.V. J. Mol. Graphics. 1993; 11: 127-138Crossref Scopus (1249) Google Scholar). Data Collection and Structure Refinement—Details of the data collection and structure refinement are shown in Tables I and II. Data were collected to a maximum of 2.09–1.55 Å resolution, with R and Rfree for the final models from ∼0.188–0.208 and from 0.209–0.227, respectively. All structures show excellent electron density over the course of the polypeptide chain, with the exception of the disordered loop between residues 177–195 and the final 10 residues of the C terminus, which were also absent in the native structures (4.Patenaude S.I. Seto N.O. Borisova S.N. Szpacenko A. Marcus S.L. Palcic M.M. Evans S.V. Nat. Struct. Biol. 2002; 9: 685-690Crossref PubMed Scopus (201) Google Scholar). These data sets (see Table I) are GTA + 3-deoxy inhibitor (GTA+DI), GTB + 3-deoxy inhibitor (GTB+DI), GTA + 3-amino inhibitor (GTA+AI), and GTB + 3-amino inhibitor (GTB+AI). UDP was present in the soaking solution of four crystals, and UDP appears clearly in the corresponding electron density maps. These data sets (see Table II) are GTA + 3-amino inhibitor + UDP (GTA+AI+UDP), and GTB + 3-amino inhibitor + UDP (GTB+AI+UDP). GTA and GTB were also co-crystallized with 3-amino inhibitors in the presence of UDP-GalNAc and UDP-Gal, respectively, (GTA+AI+UDP-GalNAc and GTB+AI+ UDP-Gal). The structures have been deposited with the Protein Data Bank with accession codes 1R7T, 1R7U, 1R7V, 1R7X, 1R7Y, 1R80, 1R81, and 1R82, respectively.Table IData collection and structure refinement statistics for GTA and GTB crystallized with inhibitors in the absence of UDPData setGTA + DIaDI = 3-deoxy inhibitor.GTB + DIGTA + AIbAI = 3-amino inhibitor.GTB + AIResolution (Å)20-2.0920-1.6120-2.0920-1.97Space groupC2221C2221C2221C2221 a (Å)52.552.652.652.4 b (Å)149.5149.9150.6150.2 c (Å)79.879.079.779.2R-merge (%)cValues in parentheses represent highest resolution shell.,dR-merge, Σ|Iobs — Iave|/ΣIave.5.1 (37.9)5.2 (37.0)4.6 (37.6)5.6 (38.3)Completeness (%)aDI = 3-deoxy inhibitor.98.1 (96.4)98.5 (87.4)96.6 (91.9)98.3 (99.8)Unique reflections18,77740,50418,56022,211Refinement resolution (Å)20-2.0920-1.6120-2.0920-1.97R-work (%)cValues in parentheses represent highest resolution shell.,eR-work, Σ|Fo| — |Fc||/Σ|Fo|.18.8 (20.9)19.6 (22.1)19.9 (24.9)19.3 (19.7)R-free (%)cValues in parentheses represent highest resolution shell.,f10% of reflections were omitted in R-free calculations.22.8 (21.4)20.9 (24.3)23.7 (27.0)22.6 (25.9)rms bond (Å)grms, root-mean-square.0.0060.0050.0060.005rms angle (°)1.31.31.21.3a DI = 3-deoxy inhibitor.b AI = 3-amino inhibitor.c Values in parentheses represent highest resolution shell.d R-merge, Σ|Iobs — Iave|/ΣIave.e R-work, Σ|Fo| — |Fc||/Σ|Fo|.f 10% of reflections were omitted in R-free calculations.g rms, root-mean-square. Open table in a new tab Table IIData collection and structure refinement statistics for GTA and GTB crystallized with inhibitors in the presence of UDP or UDP-donorData setGTA + AIaAI = 3-amino inhibitor + UDPGTB + AI + UDPGTA + AI + UDP-GalNAcGTB + AI + UDP-GalResolution (Å)50-1.7550-1.6550-1.7550-1.55Space groupC2221C2221C2221C2221 a (Å)52.552.652.652.8 b (Å)149.4150.5149.4150.4 c (Å)79.479.379.779.5R-merge (%)bValues in parentheses represent highest resolution shell.,cR-merge, Σ|Iobs — Iave|/ΣIave.4.6 (14.8)3.6 (9.5)4.0 (14.8)4.3 (52.5)Completeness (%)dDI, 3-deoxy inhibitor.99.1 (99.0)99.9 (100)99.6 (100)99.1 (97.7)Unique reflections32,16438,31532,01045,914Refinement resolution (Å)20-1.7520-1.6520-1.7520-1.55R-work (%)bValues in parentheses represent highest resolution shell.,eR-work = Σ||Fo| — |Fc||/Σ|Fo|20.7 (19.4)20.8 (20.4)21.0 (21.6)22.2 (25.5)R-free (%)bValues in parentheses represent highest resolution shell.,f10% of reflections were omitted in R-free calculations.21.5 (22.4)22.7 (23.0)22.3 (23.9)24.2 (31.6)rms bond (Å)grms, root-mean-square.0.0050.0050.0050.005rms angle (°)1.31.31.31.3a AI = 3-amino inhibitorb Values in parentheses represent highest resolution shell.c R-merge, Σ|Iobs — Iave|/ΣIave.d DI, 3-deoxy inhibitor.e R-work = Σ||Fo| — |Fc||/Σ|Fo|f 10% of reflections were omitted in R-free calculations.g rms, root-mean-square. Open table in a new tab Structural Analysis of 3-Deoxy Acceptor Analog—The 3-deoxy acceptor analog of the H-disaccharide bound to both GTA and GTB in the absence of UDP (Fig. 2, a and b), which was surprising given that UDP is known to form an integral part of the acceptor-binding site (4.Patenaude S.I. Seto N.O. Borisova S.N. Szpacenko A. Marcus S.L. Palcic M.M. Evans S.V. Nat. Struct. Biol. 2002; 9: 685-690Crossref PubMed Scopus (201) Google Scholar). This 3-deoxy inhibitor has the same overall conformation and binding interactions observed for the GTA and GTB structures containing H-antigen and UDP (Fig. 3a; Ref. 4.Patenaude S.I. Seto N.O. Borisova S.N. Szpacenko A. Marcus S.L. Palcic M.M. Evans S.V. Nat. Struct. Biol. 2002; 9: 685-690Crossref PubMed Scopus (201) Google Scholar). No significant changes in polypeptide structures were observed. The acceptor analog displayed the same position and orientation in the binding site as the native acceptor (Fig. 4a; Ref. 4.Patenaude S.I. Seto N.O. Borisova S.N. Szpacenko A. Marcus S.L. Palcic M.M. Evans S.V. Nat. Struct. Biol. 2002; 9: 685-690Crossref PubMed Scopus (201) Google Scholar). As in the structures of the native the of the acceptor analog occupies a different specific in GTA and GTB to the presence of in GTB with the in GTA (Fig. 2, a and Ref. 4.Patenaude S.I. Seto N.O. Borisova S.N. Szpacenko A. Marcus S.L. Palcic M.M. Evans S.V. Nat. Struct. Biol. 2002; 9: 685-690Crossref PubMed Scopus (201) Google Scholar). The conformation and orientation of the analog not with the presence of UDP not These observations are with the reported for the 3-deoxy analog that it as a competitive inhibitor of the H-antigen with (5.Lowary T.L. Hindsgaul O. Carbohydr. Res. 1993; 249: 163-195Crossref PubMed Scopus (61) Google observed between GTB and 3-deoxy inhibitor and 3-amino inhibitor both in the absence of UDP. The made by GTA with these two acceptor analogs are except for which with the 3-amino of the binding of GTA and GTB with the acceptor the of residues and and and DI bound to GTA and GTB AI bound to GTA and GTB in the absence of UDP. AI bound to GTA and GTB in the presence of UDP This analog from the H-disaccharide acceptor by the of the 3-OH group on the Gal residue and the transfer of from it was that this the of enzyme with acceptor analog and However, to UDP-GalNAc and UDP-Gal with GTA and GTB, respectively, not electron density corresponding to the donor density with by UDP was observed to that described for the 3-amino of Acceptor the 3-deoxy the data the 3-amino analog that was a complex mode of binding in inhibition of both GTA and GTB T.L. Hindsgaul O. Carbohydr. Res. 1994; 251: 33-67Crossref PubMed Scopus (91) Google Scholar). the electron density the acceptor analogs in GTA and GTB to the 3-amino analog crystallized in the absence (Fig. 2, c and and presence (Fig. 2, and of UDP. In the absence of UDP, the analog is to a conformation that is significantly different from that observed for either the native acceptor or 3-deoxy analog, which is by the presence of the amino This group be at pH and is observed in the crystal structures of the to form a hydrogen bond with on of the This new conformation has the Gal residue in the same as the native acceptor, with the of the and hydrogen observed in structures (Fig. with the that the l-Fuc residue the surface of the and the by UDP. This new position is further by the of a new hydrogen bond from Fuc a to residue in both GTA and GTB and In the presence of UDP, the Gal moiety of the 3-amino analog in the same position observed for the native acceptor and The residue is the 3-amino analog to abandon the intramolecular hydrogen bond and the hydrogen bond to the The ring a less ordered with with part of the enzyme (Fig. and displays significantly temperature the Gal As with the 3-deoxy analog, made to the 3-amino analog with GTA and GTB in the presence of UDP-GalNAc and UDP-Gal not a density corresponding to either as was found for the analog, the enzyme was to significant of donor over the such that for UDP was observed. In these crystal structures (GTA+AI+UDP-GalNAc and excellent density was observed for the Gal but the l-Fuc residue was in GTA over the two to the that the electron density corresponding to this residue was (Fig. a and The of the 3-amino acceptor analog is not to the of UDP and in the absence of UDP, the analog occupies different in GTA and GTB, which to changes in the of amino acid residue the four amino acid between GTA and GTB, residue has been shown to dominate the selection between UDP donors (4.Patenaude S.I. Seto N.O. Borisova S.N. Szpacenko A. Marcus S.L. Palcic M.M. Evans S.V. Nat. Struct. Biol. 2002; 9: 685-690Crossref PubMed Scopus (201) Google Scholar), with GTA and GTB between the binding of H-disaccharide acceptor to GTA and GTB have been in the S.L. Polakowski R. Seto N.O. Leinala E. Borisova S. Blancher A. Roubinet F. Evans S.V. Palcic M.M. J. Biol. Chem. 2003; 278: 12403-12405Abstract Full Text Full Text PDF PubMed Scopus (87) Google Scholar) and to the of both the native (4.Patenaude S.I. Seto N.O. Borisova S.N. Szpacenko A. Marcus S.L. Palcic M.M. Evans S.V. Nat. Struct. Biol. 2002; 9: 685-690Crossref PubMed Scopus (201) Google Scholar) and the 3-deoxy acceptor analogs in GTA and GTB are nearly The in position observed for the 3-amino analog the that Leu/Met-266 can have on acceptor although the are to in the of the acceptor they are at the same position as the glycoprotein or glycolipid substrate of the A and B and their the of these substrates by GTA and GTB (4.Patenaude S.I. Seto N.O. Borisova S.N. Szpacenko A. Marcus S.L. Palcic M.M. Evans S.V. Nat. Struct. Biol. 2002; 9: 685-690Crossref PubMed Scopus (201) Google Scholar). the of the observed for the where the in conformation is to that observed in the native and can be to one of the four residue between GTA and GTB The observed of the Fuc residue to form a hydrogen bond with the 3-amino Gal in the absence of UDP a in the binding site which the (Fig. The presence of UDP in the binding site the Fuc ring on the inhibitor to disordered but the to the same general conformation. The crystal structures of the 3-deoxy and 3-amino analogs in complex with GTA and GTB show that the binding of these H-antigen acceptor analogs are with their observed activity as inhibitors of acceptor binding in GTA and GTB. The binding of the 3-amino analog a from that displayed by the H-disaccharide acceptor and 3-deoxy analog, where this binding changes in the presence or absence of UDP. given that GTA and GTB share a common acceptor, the binding of acceptor analog is significantly by the enzyme is GTA or GTB. The of the 3-amino acceptor with UDP for the same binding site in the is with the observed complex mode of inhibition.

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.