The Molecular Basis for the Absence ofN-Glycolylneuraminic Acid in Humans

N-Glycolylneuraminic acid (NeuGc) is abundantly expressed in most mammals, but it is not detectable in humans. The expression of NeuGc is controlled by cytidine monophospho-N-acetylneuraminic acid (CMP-NeuAc) hydroxylase activity. We previously cloned a cDNA for mouse CMP-NeuAc hydroxylase and found that the human genome contains a homologue. We report here the molecular basis for the absence of NeuGc in humans. We cloned a cDNA for human CMP-NeuAc hydroxylase from a HeLa cell cDNA library. The cDNA encodes a 486-amino acid protein, and its deduced amino acid sequence lacks a domain corresponding to the N-terminal 104 amino acids of the mouse CMP-NeuAc hydroxylase protein, although the human protein is highly identical (93%) to the rest of the mouse hydroxylase protein. The N-terminal truncation of the human hydroxylase is caused by deletion of a 92-base pair-long exon in human genomic DNA. The human hydroxylase expressed in COS-7 cells exhibited no enzymatic activity, and a mouse hydroxylase mutant, which lacks the N-terminal domain, was also inactive. A chimera composed of the human hydroxylase and the N-terminal domain of the mouse hydroxylase displayed the enzyme activity. These results indicate that the human homologue of CMP-NeuAc hydroxylase is inactive because it lacks an N-terminal domain that is essential for enzyme activity. The absence of NeuGc in human glycoconjugates is due to a partial deletion in the gene that encodes CMP-NeuAc hydroxylase. N-Glycolylneuraminic acid (NeuGc) is abundantly expressed in most mammals, but it is not detectable in humans. The expression of NeuGc is controlled by cytidine monophospho-N-acetylneuraminic acid (CMP-NeuAc) hydroxylase activity. We previously cloned a cDNA for mouse CMP-NeuAc hydroxylase and found that the human genome contains a homologue. We report here the molecular basis for the absence of NeuGc in humans. We cloned a cDNA for human CMP-NeuAc hydroxylase from a HeLa cell cDNA library. The cDNA encodes a 486-amino acid protein, and its deduced amino acid sequence lacks a domain corresponding to the N-terminal 104 amino acids of the mouse CMP-NeuAc hydroxylase protein, although the human protein is highly identical (93%) to the rest of the mouse hydroxylase protein. The N-terminal truncation of the human hydroxylase is caused by deletion of a 92-base pair-long exon in human genomic DNA. The human hydroxylase expressed in COS-7 cells exhibited no enzymatic activity, and a mouse hydroxylase mutant, which lacks the N-terminal domain, was also inactive. A chimera composed of the human hydroxylase and the N-terminal domain of the mouse hydroxylase displayed the enzyme activity. These results indicate that the human homologue of CMP-NeuAc hydroxylase is inactive because it lacks an N-terminal domain that is essential for enzyme activity. The absence of NeuGc in human glycoconjugates is due to a partial deletion in the gene that encodes CMP-NeuAc hydroxylase. Sialic acids are components of the carbohydrate chains of glycoconjugates and are involved in cell-cell recognition (1Rutishauser U. Acheson A. Hall A.K. Mann D.M. Sunshine J. Science. 1988; 240: 53-57Crossref PubMed Scopus (671) Google Scholar, 2Kelm S. Schauer R. Crocker P.R. Glycoconj. J. 1996; 13: 913-926Crossref PubMed Scopus (108) Google Scholar) and cell-pathogen interactions (3Smit H. Gaastra W. Kamerling J.P. Vliegenthart J.F. de Graaf F.K. Infect. Immun. 1984; 46: 578-584Crossref PubMed Google Scholar, 4Suzuki Y. Nagao Y. Kato H. Suzuki T. Matsumoto M. Murayama J. Biochim. Biophys. Acta. 1987; 903: 417-424Crossref PubMed Scopus (47) Google Scholar). Sialic acid is a generic designation used for N-acylneuraminic acids and their derivatives (5,6Varki A. Glycobiology. 1992; 2: 25-40Crossref PubMed Scopus (479) Google Scholar). N-Acetylneuraminic acid (NeuAc) 1The abbreviations used are: NeuAc,N-acetylneuraminic acid; NeuGc,N-glycolylneuraminic acid; CMP-NeuAc, cytidine monophospho-N-acetylneuraminic acid; RT-PCR, reverse transcriptase-polymerase chain reaction; bp, base pair(s). 1The abbreviations used are: NeuAc,N-acetylneuraminic acid; NeuGc,N-glycolylneuraminic acid; CMP-NeuAc, cytidine monophospho-N-acetylneuraminic acid; RT-PCR, reverse transcriptase-polymerase chain reaction; bp, base pair(s). andN-glycolylneuraminic acid (NeuGc) are two of the most abundant derivatives. Previous studies suggest that some adhesion molecules recognize glycoconjugates containing NeuGc and NeuAc with different affinities. Sialoadhesin, a cell adhesion molecule of marginal zone macrophages, recognizes NeuAcα2–3Gal but not NeuGcα2–3Gal (7Kelm S. Schauer R. Manuguerra J.C. Gross H.J. Crocker P.R. Glycoconj. J. 1994; 11: 576-585Crossref PubMed Scopus (179) Google Scholar). On the other hand, mouse CD22, a B cell-restricted adhesion molecule, binds more strongly to NeuGcα2–6Gal than to NeuAcα2–6Gal (7Kelm S. Schauer R. Manuguerra J.C. Gross H.J. Crocker P.R. Glycoconj. J. 1994; 11: 576-585Crossref PubMed Scopus (179) Google Scholar). Influenza hemagglutinins recognize glycoconjugates that contain NeuAc and NeuGc with different affinities (8Higa H.H. Rogers G.N. Paulson J.C. Virology. 1985; 144: 279-282Crossref PubMed Scopus (113) Google Scholar). These studies suggest that the diversity of sialic acids is biologically important in recognition events mediated by glycoconjugates.Although NeuGc-containing glycoconjugates are found in most mammals (5,6Varki A. Glycobiology. 1992; 2: 25-40Crossref PubMed Scopus (479) Google Scholar), NeuGc is not detectable in normal human tissues. Glycoconjugates containing NeuGc are immunogenic in human, and an antibody against NeuGc, which is known as Hanganutziu-Deicher antibody, is produced by patients who receive therapeutic injections of animal antisera (9Higashi H. Naiki M. Matuo S. Okouchi K. Biochem. Biophys. Res. Commun. 1977; 79: 388-395Crossref PubMed Scopus (163) Google Scholar,10Merrick J.M. Zadarlik K. Milgrom F. Int. Arch. Allergy Appl. Immunol. 1978; 57: 477-480Crossref PubMed Scopus (112) Google Scholar).NeuGc is assumed to be produced from NeuAc through enzymatic hydroxylation of the N-acetyl residue of free NeuAc, CMP-NeuAc, or glycoconjugate-linked NeuAc (11Schauer R. Wember M. Hoppe-Seyler's Z. Physiol. Chem. 1971; 352: 1282-1290Crossref PubMed Scopus (33) Google Scholar, 12Buscher H.P. Casals-Stenzel J. Schauer R. Mestres-Ventura P. Eur. J. Biochem. 1977; 77: 297-310Crossref PubMed Scopus (40) Google Scholar). Previous studies showed that the major mechanism for biosynthesis of NeuGc is hydroxylation of CMP-NeuAc (13Shaw L. Schauer R. Biol. Chem. Hoppe-Seyler. 1988; 369: 477-486Crossref PubMed Scopus (126) Google Scholar, 14Muchmore E.A. Milewski M. Varki A. Diaz S. J. Biol. Chem. 1989; 264: 20216-20223Abstract Full PubMed Google Scholar, L. Schauer R. Biochem. J. 1989; PubMed Scopus Google Scholar, A. L. P. R. A. Schauer R. Eur. J. Biochem. PubMed Scopus Google Scholar). the of CMP-NeuAc hydroxylase a in the of NeuGc expression in We showed previously that the of CMP-NeuAc to is by an that and CMP-NeuAc hydroxylase Y. T. T. Suzuki A. J. Biochem. PubMed Scopus Google Scholar, Y. T. H. Suzuki K. T. Suzuki A. J. Biochem. PubMed Scopus Google Scholar, T. Y. H. T. Suzuki A. Glycoconj. J. PubMed Scopus Google Scholar). The of CMP-NeuAc hydroxylase the of the hydroxylation T. Y. H. T. Suzuki A. Glycoconj. J. PubMed Scopus Google Scholar). T. Y. T. Suzuki A. J. Biol. Chem. 1994; Full PubMed Google Scholar) and cloned mouse CMP-NeuAc hydroxylase T. S. H. Y. H. S. T. Suzuki A. J. Biol. Chem. Full Full PubMed Scopus Google Scholar) and showed that the of NeuGc to NeuAc in glycoconjugates is by the expression of CMP-NeuAc hydroxylase T. S. H. Y. H. S. T. Suzuki A. J. Biol. Chem. Full Full PubMed Scopus Google Scholar). The human genome contains a that with the mouse CMP-NeuAc hydroxylase cDNA T. S. H. Y. H. S. T. Suzuki A. J. Biol. Chem. Full Full PubMed Scopus Google Scholar). the molecular basis for the absence of NeuGc in cloned and expressed the human homologue. We report here that the human CMP-NeuAc hydroxylase protein is inactive because of a partial deletion in the human CMP-NeuAc hydroxylase from animal to and in the NeuGc is of the abundant derivatives of sialic acid and is expressed in most NeuGc and of sialic acids expressed in mouse and A. L. P. R. A. Schauer R. Eur. J. Biochem. PubMed Scopus Google Scholar). sialic acid in and is NeuGc Crocker P.R. M. Schauer R. S. J. Biol. Chem. 1996; Full Full PubMed Scopus Google Scholar). no expression of NeuGc was in normal human tissues. The absence of NeuGc in is by the that NeuGc is highly immunogenic to humans. that recognize containing NeuGc of animal to (9Higashi H. Naiki M. Matuo S. Okouchi K. Biochem. Biophys. Res. Commun. 1977; 79: 388-395Crossref PubMed Scopus (163) Google Scholar, J.M. Zadarlik K. Milgrom F. Int. Arch. Allergy Appl. Immunol. 1978; 57: 477-480Crossref PubMed Scopus (112) Google Scholar). of the absence of a carbohydrate sequence and its in is the is expressed in mammals but not in and U. J. Biol. Chem. 1988; Full PubMed Google Scholar). against glycoconjugates containing the are in U. J. J. 1985; PubMed Scopus Google Scholar). The for the absence of the in is that human gene is a which contains in because of J. Biol. Chem. Full PubMed Google Scholar, J. Biol. Chem. Full PubMed Google Scholar). The molecular mechanism for the absence of NeuGc from that of the of the human genome that the CMP-NeuAc hydroxylase gene is in human genome in not for the human CMP-NeuAc hydroxylase homologue is and and the protein was the human hydroxylase is inactive because of the deletion of exon in the hydroxylase genome in the of the mouse CMP-NeuAc hydroxylase is essential for enzyme activity. W. L. S. F. Schauer R. 1996; PubMed Scopus Google Scholar) cloned a partial cDNA for CMP-NeuAc hydroxylase and that CMP-NeuAc hydroxylase is an protein of the and the N-terminal domain of the mouse CMP-NeuAc hydroxylase contains the for the essential of domain for hydroxylase is by the in W. L. S. F. Schauer R. 1996; PubMed Scopus Google Scholar) also that the for CMP-NeuAc and for are in the of the mouse CMP-NeuAc hydroxylase are no the for CMP-NeuAc or are highly in the the and the human acid of are to but the amino acid of the the and the human are highly the human hydroxylase is inactive. We cloned a cDNA for a mouse CMP-NeuAc hydroxylase that lacks amino acids in the of the normal hydroxylase S. T. H. T. Y. Suzuki A. T. Glycoconj. J. 1996; 13: PubMed Scopus Google Scholar). The is expressed in mouse and no enzyme activity. The of the is of hydroxylase S. T. H. T. Y. Suzuki A. T. Glycoconj. J. 1996; 13: PubMed Scopus Google Scholar). The of the inactive mouse is the of the inactive human hydroxylase and the inactive mouse hydroxylase the of other of CMP-NeuAc hydroxylase. studies are to absence of NeuGc results in a partial of diversity of human binds more strongly to NeuGcα2–6Gal than to NeuAcα2–6Gal (7Kelm S. Schauer R. Manuguerra J.C. Gross H.J. Crocker P.R. Glycoconj. J. 1994; 11: 576-585Crossref PubMed Scopus (179) Google Scholar, Crocker P.R. M. Schauer R. S. J. Biol. Chem. 1996; Full Full PubMed Scopus Google Scholar). On the other hand, human binds to NeuAcα2–6Gal and to NeuGcα2–6Gal S. Schauer R. Crocker P.R. Glycoconj. J. 1996; 13: 913-926Crossref PubMed Scopus (108) Google Scholar), NeuAc for NeuGc in the of human of the expression of NeuGc-containing in S. S. S. J. A. T. J. Biochem. 1978; PubMed Scopus Google Scholar, Y. T. Y. J. Biochem. 1984; PubMed Scopus Google Scholar), S. S. J. A. T. J. Biochem. PubMed Scopus Google Scholar), and J.F. J. Biol. Chem. 1988; Full PubMed Google Scholar). These studies suggest that NeuGc is not essential for it is that NeuAc or other components of cells for the of NeuGc in or in The absence of NeuGc against by an of to but not to in cells (3Smit H. Gaastra W. Kamerling J.P. Vliegenthart J.F. de Graaf F.K. Infect. Immun. 1984; 46: 578-584Crossref PubMed Google Scholar). in and which On the other hand, not to human because of the absence of in K. Infect. Immun. 1984; PubMed Google Scholar). These results indicate that the of diversity of sialic acids is not to studies that human cells NeuGc-containing glycoconjugates A. Glycobiology. 1992; 2: 25-40Crossref PubMed Scopus (479) Google Scholar), but are of studies used against NeuGc-containing but not to NeuGc in a studies the of NeuGc expression in by their results are also K. H. J. Biol. Chem. 1988; Full PubMed Google Scholar) that no NeuGc expression was in human or cell but H. K. A. R. S. Res. 1996; Google Scholar) that NeuGc-containing expressed in tissues. the of the biosynthesis of NeuGc by CMP-NeuAc hydroxylation in humans. We that the hydroxylation of CMP-NeuAc is the major and that other because the of and of CMP-NeuAc hydroxylase with the expression of NeuGc T. S. H. Y. H. S. T. Suzuki A. J. Biol. Chem. Full Full PubMed Scopus Google Scholar). that the NeuGc is by the hydroxylation of CMP-NeuAc, and molecular for the expression of NeuGc in human to be NeuGc and hydroxylase are in On the basis of molecular of CMP-NeuAc of is in in to the partial deletion of the hydroxylase genome in that the human CMP-NeuAc hydroxylase is the inactive protein because of the of the N-terminal domain, which is essential for CMP-NeuAc hydroxylase activity. We that the absence of NeuGc in is due to the deletion of exon in CMP-NeuAc hydroxylase to of molecular basis for the diversity of in Sialic acids are components of the carbohydrate chains of glycoconjugates and are involved in cell-cell recognition (1Rutishauser U. Acheson A. Hall A.K. Mann D.M. Sunshine J. Science. 1988; 240: 53-57Crossref PubMed Scopus (671) Google Scholar, 2Kelm S. Schauer R. Crocker P.R. Glycoconj. J. 1996; 13: 913-926Crossref PubMed Scopus (108) Google Scholar) and cell-pathogen interactions (3Smit H. Gaastra W. Kamerling J.P. Vliegenthart J.F. de Graaf F.K. Infect. Immun. 1984; 46: 578-584Crossref PubMed Google Scholar, 4Suzuki Y. Nagao Y. Kato H. Suzuki T. Matsumoto M. Murayama J. Biochim. Biophys. Acta. 1987; 903: 417-424Crossref PubMed Scopus (47) Google Scholar). Sialic acid is a generic designation used for N-acylneuraminic acids and their derivatives (5,6Varki A. Glycobiology. 1992; 2: 25-40Crossref PubMed Scopus (479) Google Scholar). N-Acetylneuraminic acid (NeuAc) 1The abbreviations used are: NeuAc,N-acetylneuraminic acid; NeuGc,N-glycolylneuraminic acid; CMP-NeuAc, cytidine monophospho-N-acetylneuraminic acid; RT-PCR, reverse transcriptase-polymerase chain reaction; bp, base pair(s). 1The abbreviations used are: NeuAc,N-acetylneuraminic acid; NeuGc,N-glycolylneuraminic acid; CMP-NeuAc, cytidine monophospho-N-acetylneuraminic acid; RT-PCR, reverse transcriptase-polymerase chain reaction; bp, base pair(s). andN-glycolylneuraminic acid (NeuGc) are two of the most abundant derivatives. Previous studies suggest that some adhesion molecules recognize glycoconjugates containing NeuGc and NeuAc with different affinities. Sialoadhesin, a cell adhesion molecule of marginal zone macrophages, recognizes NeuAcα2–3Gal but not NeuGcα2–3Gal (7Kelm S. Schauer R. Manuguerra J.C. Gross H.J. Crocker P.R. Glycoconj. J. 1994; 11: 576-585Crossref PubMed Scopus (179) Google Scholar). On the other hand, mouse CD22, a B cell-restricted adhesion molecule, binds more strongly to NeuGcα2–6Gal than to NeuAcα2–6Gal (7Kelm S. Schauer R. Manuguerra J.C. Gross H.J. Crocker P.R. Glycoconj. J. 1994; 11: 576-585Crossref PubMed Scopus (179) Google Scholar). Influenza hemagglutinins recognize glycoconjugates that contain NeuAc and NeuGc with different affinities (8Higa H.H. Rogers G.N. Paulson J.C. Virology. 1985; 144: 279-282Crossref PubMed Scopus (113) Google Scholar). These studies suggest that the diversity of sialic acids is biologically important in recognition events mediated by NeuGc-containing glycoconjugates are found in most mammals (5,6Varki A. Glycobiology. 1992; 2: 25-40Crossref PubMed Scopus (479) Google Scholar), NeuGc is not detectable in normal human tissues. Glycoconjugates containing NeuGc are immunogenic in human, and an antibody against NeuGc, which is known as Hanganutziu-Deicher antibody, is produced by patients who receive therapeutic injections of animal antisera (9Higashi H. Naiki M. Matuo S. Okouchi K. Biochem. Biophys. Res. Commun. 1977; 79: 388-395Crossref PubMed Scopus (163) Google Scholar,10Merrick J.M. Zadarlik K. Milgrom F. Int. Arch. Allergy Appl. Immunol. 1978; 57: 477-480Crossref PubMed Scopus (112) Google Scholar). NeuGc is assumed to be produced from NeuAc through enzymatic hydroxylation of the N-acetyl residue of free NeuAc, CMP-NeuAc, or glycoconjugate-linked NeuAc (11Schauer R. Wember M. Hoppe-Seyler's Z. Physiol. Chem. 1971; 352: 1282-1290Crossref PubMed Scopus (33) Google Scholar, 12Buscher H.P. Casals-Stenzel J. Schauer R. Mestres-Ventura P. Eur. J. Biochem. 1977; 77: 297-310Crossref PubMed Scopus (40) Google Scholar). Previous studies showed that the major mechanism for biosynthesis of NeuGc is hydroxylation of CMP-NeuAc (13Shaw L. Schauer R. Biol. Chem. Hoppe-Seyler. 1988; 369: 477-486Crossref PubMed Scopus (126) Google Scholar, 14Muchmore E.A. Milewski M. Varki A. Diaz S. J. Biol. Chem. 1989; 264: 20216-20223Abstract Full PubMed Google Scholar, L. Schauer R. Biochem. J. 1989; PubMed Scopus Google Scholar, A. L. P. R. A. Schauer R. Eur. J. Biochem. PubMed Scopus Google Scholar). the of CMP-NeuAc hydroxylase a in the of NeuGc expression in We showed previously that the of CMP-NeuAc to is by an that and CMP-NeuAc hydroxylase Y. T. T. Suzuki A. J. Biochem. PubMed Scopus Google Scholar, Y. T. H. Suzuki K. T. Suzuki A. J. Biochem. PubMed Scopus Google Scholar, T. Y. H. T. Suzuki A. Glycoconj. J. PubMed Scopus Google Scholar). The of CMP-NeuAc hydroxylase the of the hydroxylation T. Y. H. T. Suzuki A. Glycoconj. J. PubMed Scopus Google Scholar). T. Y. T. Suzuki A. J. Biol. Chem. 1994; Full PubMed Google Scholar) and cloned mouse CMP-NeuAc hydroxylase T. S. H. Y. H. S. T. Suzuki A. J. Biol. Chem. Full Full PubMed Scopus Google Scholar) and showed that the of NeuGc to NeuAc in glycoconjugates is by the expression of CMP-NeuAc hydroxylase T. S. H. Y. H. S. T. Suzuki A. J. Biol. Chem. Full Full PubMed Scopus Google Scholar). The human genome contains a that with the mouse CMP-NeuAc hydroxylase cDNA T. S. H. Y. H. S. T. Suzuki A. J. Biol. Chem. Full Full PubMed Scopus Google Scholar). the molecular basis for the absence of NeuGc in cloned and expressed the human homologue. We report here that the human CMP-NeuAc hydroxylase protein is inactive because of a partial deletion in the human CMP-NeuAc hydroxylase from animal to and in the NeuGc is of the abundant derivatives of sialic acid and is expressed in most NeuGc and of sialic acids expressed in mouse and A. L. P. R. A. Schauer R. Eur. J. Biochem. PubMed Scopus Google Scholar). sialic acid in and is NeuGc Crocker P.R. M. Schauer R. S. J. Biol. Chem. 1996; Full Full PubMed Scopus Google Scholar). no expression of NeuGc was in normal human tissues. The absence of NeuGc in is by the that NeuGc is highly immunogenic to humans. that recognize containing NeuGc of animal to (9Higashi H. Naiki M. Matuo S. Okouchi K. Biochem. Biophys. Res. Commun. 1977; 79: 388-395Crossref PubMed Scopus (163) Google Scholar, J.M. Zadarlik K. Milgrom F. Int. Arch. Allergy Appl. Immunol. 1978; 57: 477-480Crossref PubMed Scopus (112) Google Scholar). of the absence of a carbohydrate sequence and its in is the is expressed in mammals but not in and U. J. Biol. Chem. 1988; Full PubMed Google Scholar). against glycoconjugates containing the are in U. J. J. 1985; PubMed Scopus Google Scholar). The for the absence of the in is that human gene is a which contains in because of J. Biol. Chem. Full PubMed Google Scholar, J. Biol. Chem. Full PubMed Google Scholar). The molecular mechanism for the absence of NeuGc from that of the of the human genome that the CMP-NeuAc hydroxylase gene is in human genome in not for the human CMP-NeuAc hydroxylase homologue is and and the protein was the human hydroxylase is inactive because of the deletion of exon in the hydroxylase genome in the of the mouse CMP-NeuAc hydroxylase is essential for enzyme activity. W. L. S. F. Schauer R. 1996; PubMed Scopus Google Scholar) cloned a partial cDNA for CMP-NeuAc hydroxylase and that CMP-NeuAc hydroxylase is an protein of the and the N-terminal domain of the mouse CMP-NeuAc hydroxylase contains the for the essential of domain for hydroxylase is by the in W. L. S. F. Schauer R. 1996; PubMed Scopus Google Scholar) also that the for CMP-NeuAc and for are in the of the mouse CMP-NeuAc hydroxylase are no the for CMP-NeuAc or are highly in the the and the human acid of are to but the amino acid of the the and the human are highly the human hydroxylase is inactive. We cloned a cDNA for a mouse CMP-NeuAc hydroxylase that lacks amino acids in the of the normal hydroxylase S. T. H. T. Y. Suzuki A. T. Glycoconj. J. 1996; 13: PubMed Scopus Google Scholar). The is expressed in mouse and no enzyme activity. The of the is of hydroxylase S. T. H. T. Y. Suzuki A. T. Glycoconj. J. 1996; 13: PubMed Scopus Google Scholar). The of the inactive mouse is the of the inactive human hydroxylase and the inactive mouse hydroxylase the of other of CMP-NeuAc hydroxylase. studies are to absence of NeuGc results in a partial of diversity of human binds more strongly to NeuGcα2–6Gal than to NeuAcα2–6Gal (7Kelm S. Schauer R. Manuguerra J.C. Gross H.J. Crocker P.R. Glycoconj. J. 1994; 11: 576-585Crossref PubMed Scopus (179) Google Scholar, Crocker P.R. M. Schauer R. S. J. Biol. Chem. 1996; Full Full PubMed Scopus Google Scholar). On the other hand, human binds to NeuAcα2–6Gal and to NeuGcα2–6Gal S. Schauer R. Crocker P.R. Glycoconj. J. 1996; 13: 913-926Crossref PubMed Scopus (108) Google Scholar), NeuAc for NeuGc in the of human of the expression of NeuGc-containing in S. S. S. J. A. T. J. Biochem. 1978; PubMed Scopus Google Scholar, Y. T. Y. J. Biochem. 1984; PubMed Scopus Google Scholar), S. S. J. A. T. J. Biochem. PubMed Scopus Google Scholar), and J.F. J. Biol. Chem. 1988; Full PubMed Google Scholar). These studies suggest that NeuGc is not essential for it is that NeuAc or other components of cells for the of NeuGc in or in The absence of NeuGc against by an of to but not to in cells (3Smit H. Gaastra W. Kamerling J.P. Vliegenthart J.F. de Graaf F.K. Infect. Immun. 1984; 46: 578-584Crossref PubMed Google Scholar). in and which On the other hand, not to human because of the absence of in K. Infect. Immun. 1984; PubMed Google Scholar). These results indicate that the of diversity of sialic acids is not to studies that human cells NeuGc-containing glycoconjugates A. Glycobiology. 1992; 2: 25-40Crossref PubMed Scopus (479) Google Scholar), but are of studies used against NeuGc-containing but not to NeuGc in a studies the of NeuGc expression in by their results are also K. H. J. Biol. Chem. 1988; Full PubMed Google Scholar) that no NeuGc expression was in human or cell but H. K. A. R. S. Res. 1996; Google Scholar) that NeuGc-containing expressed in tissues. the of the biosynthesis of NeuGc by CMP-NeuAc hydroxylation in humans. We that the hydroxylation of CMP-NeuAc is the major and that other because the of and of CMP-NeuAc hydroxylase with the expression of NeuGc T. S. H. Y. H. S. T. Suzuki A. J. Biol. Chem. Full Full PubMed Scopus Google Scholar). that the NeuGc is by the hydroxylation of CMP-NeuAc, and molecular for the expression of NeuGc in human to be NeuGc and hydroxylase are in On the basis of molecular of CMP-NeuAc of is in in to the partial deletion of the hydroxylase genome in that the human CMP-NeuAc hydroxylase is the inactive protein because of the of the N-terminal domain, which is essential for CMP-NeuAc hydroxylase activity. We that the absence of NeuGc in is due to the deletion of exon in CMP-NeuAc hydroxylase to of molecular basis for the diversity of in from animal to and in the NeuGc is of the abundant derivatives of sialic acid and is expressed in most NeuGc and of sialic acids expressed in mouse and A. L. P. R. A. Schauer R. Eur. J. Biochem. PubMed Scopus Google Scholar). sialic acid in and is NeuGc Crocker P.R. M. Schauer R. S. J. Biol. Chem. 1996; Full Full PubMed Scopus Google Scholar). no expression of NeuGc was in normal human tissues. The absence of NeuGc in is by the that NeuGc is highly immunogenic to humans. that recognize containing NeuGc of animal to (9Higashi H. Naiki M. Matuo S. Okouchi K. Biochem. Biophys. Res. Commun. 1977; 79: 388-395Crossref PubMed Scopus (163) Google Scholar, J.M. Zadarlik K. Milgrom F. Int. Arch. Allergy Appl. Immunol. 1978; 57: 477-480Crossref PubMed Scopus (112) Google Scholar). of the absence of a carbohydrate sequence and its in is the is expressed in mammals but not in and U. J. Biol. Chem. 1988; Full PubMed Google Scholar). against glycoconjugates containing the are in U. J. J. 1985; PubMed Scopus Google Scholar). The for the absence of the in is that human gene is a which contains in because of J. Biol. Chem. Full PubMed Google Scholar, J. Biol. Chem. Full PubMed Google Scholar). The molecular mechanism for the absence of NeuGc from that of the of the human genome that the CMP-NeuAc hydroxylase gene is in human genome in not for the human CMP-NeuAc hydroxylase homologue is and and the protein was the human hydroxylase is inactive because of the deletion of exon in the hydroxylase genome in the of the mouse CMP-NeuAc hydroxylase is essential for enzyme activity. W. L. S. F. Schauer R. 1996; PubMed Scopus Google Scholar) cloned a partial cDNA for CMP-NeuAc hydroxylase and that CMP-NeuAc hydroxylase is an protein of the and the N-terminal domain of the mouse CMP-NeuAc hydroxylase contains the for the essential of domain for hydroxylase is by the in W. L. S. F. Schauer R. 1996; PubMed Scopus Google Scholar) also that the for CMP-NeuAc and for are in the of the mouse CMP-NeuAc hydroxylase are no the for CMP-NeuAc or are highly in the the and the human acid of are to but the amino acid of the the and the human are highly the human hydroxylase is inactive. We cloned a cDNA for a mouse CMP-NeuAc hydroxylase that lacks amino acids in the of the normal hydroxylase S. T. H. T. Y. Suzuki A. T. Glycoconj. J. 1996; 13: PubMed Scopus Google Scholar). The is expressed in mouse and no enzyme activity. The of the is of hydroxylase S. T. H. T. Y. Suzuki A. T. Glycoconj. J. 1996; 13: PubMed Scopus Google Scholar). The of the inactive mouse is the of the inactive human hydroxylase and the inactive mouse hydroxylase the of other of CMP-NeuAc hydroxylase. studies are to The absence of NeuGc results in a partial of diversity of human binds more strongly to NeuGcα2–6Gal than to NeuAcα2–6Gal (7Kelm S. Schauer R. Manuguerra J.C. Gross H.J. Crocker P.R. Glycoconj. J. 1994; 11: 576-585Crossref PubMed Scopus (179) Google Scholar, Crocker P.R. M. Schauer R. S. J. Biol. Chem. 1996; Full Full PubMed Scopus Google Scholar). On the other hand, human binds to NeuAcα2–6Gal and to NeuGcα2–6Gal S. Schauer R. Crocker P.R. Glycoconj. J. 1996; 13: 913-926Crossref PubMed Scopus (108) Google Scholar), NeuAc for NeuGc in the of human of the expression of NeuGc-containing in S. S. S. J. A. T. J. Biochem. 1978; PubMed Scopus Google Scholar, Y. T. Y. J. Biochem. 1984; PubMed Scopus Google Scholar), S. S. J. A. T. J. Biochem. PubMed Scopus Google Scholar), and J.F. J. Biol. Chem. 1988; Full PubMed Google Scholar). These studies suggest that NeuGc is not essential for it is that NeuAc or other components of cells for the of NeuGc in or in The absence of NeuGc against by an of to but not to in cells (3Smit H. Gaastra W. Kamerling J.P. Vliegenthart J.F. de Graaf F.K. Infect. Immun. 1984; 46: 578-584Crossref PubMed Google Scholar). in and which On the other hand, not to human because of the absence of in K. Infect. Immun. 1984; PubMed Google Scholar). These results indicate that the of diversity of sialic acids is not to humans. studies that human cells NeuGc-containing glycoconjugates A. Glycobiology. 1992; 2: 25-40Crossref PubMed Scopus (479) Google Scholar), but are of studies used against NeuGc-containing but not to NeuGc in a studies the of NeuGc expression in by their results are also K. H. J. Biol. Chem. 1988; Full PubMed Google Scholar) that no NeuGc expression was in human or cell but H. K. A. R. S. Res. 1996; Google Scholar) that NeuGc-containing expressed in tissues. the of the biosynthesis of NeuGc by CMP-NeuAc hydroxylation in humans. We that the hydroxylation of CMP-NeuAc is the major and that other because the of and of CMP-NeuAc hydroxylase with the expression of NeuGc T. S. H. Y. H. S. T. Suzuki A. J. Biol. Chem. Full Full PubMed Scopus Google Scholar). that the NeuGc is by the hydroxylation of CMP-NeuAc, and molecular for the expression of NeuGc in human to be NeuGc and hydroxylase are in On the basis of molecular of CMP-NeuAc of is in in to the partial deletion of the hydroxylase genome in that the human CMP-NeuAc hydroxylase is the inactive protein because of the of the N-terminal domain, which is essential for CMP-NeuAc hydroxylase activity. We that the absence of NeuGc in is due to the deletion of exon in CMP-NeuAc hydroxylase to of molecular basis for the diversity of in We T. of for and and M. of for with the