Molecular cloning of the human beta1,4 N-acetylgalactosaminyltransferase responsible for the biosynthesis of the Sd(a) histo-blood group antigen: the sequence predicts a very long cytoplasmic domain.
The Sd(a) antigen is a carbohydrate determinant expressed on erythrocytes, the colonic mucosa and other tissues. This epitope, whose structure is Siaalpha2,3[GalNAcbeta1,4]Gal beta1,4GlcNAc, is synthesized by a beta1,4 N-acetylgalactosaminyltransferase (beta4GalNAc-T) that transfers a beta1,4-linked GalNAc to the galactose residue of an alpha2,3-sialylated chain. We have cloned from human colon carcinoma Caco2 cells a cDNA whose transfection in COS cells induces a GalNAc-T active on sialylated but not on asialylated fetuin and putatively represents the human Sd(a) beta4GalNAc-T. The cDNA predicts a 566 aa protein showing 66.6% and 39% identity with mouse CT beta4GalNAc-T and human GM2/GD2 synthase, respectively, with a typical type II glycosyltransferase organization, no potential N-glycosylation sites and a 67 aa cytoplasmic tail, which is probably the longest among the glycosyltransferases cloned to date. The gene maps in chromosome 17q23, and is composed of at least 11 exons. Exons 2-11 are homologous to exons 2-11 of the previously cloned CT beta4GalNAc-T from murine cytotoxic T lymphocytes while exons 1 of the two enzymes are totally different. The mRNA is expressed at a high level in differentiated Caco2 cells and in colonic mucosa and at a much lower level in lymphocytes and other colon cancer cell lines.
Lo Presti
Libera
L
Dipartimento di Patologia Sperimentale, Università di Bologna, Via S. Giacomo 14, 40126, Bologna, Italy.
Cabuy
Erik
E
Chiricolo
Mariella
M
Dall'Olio
Fabio
F
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001789:Blood Group Antigens / Q000096:biosynthesis* / Q000378:metabolism; D019556:COS Cells; D018938:Caco-2 Cells; D002886:Chromosomes, Human, Pair 17 / Q000235:genetics; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000378:metabolism*; D018076:DNA, Complementary / Q000235:genetics; D005091:Exons / Q000235:genetics; D005786:Gene Expression Regulation; D023281:Genomics; D006801:Humans; D007438:Introns / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D017350:N-Acetylgalactosaminyltransferases / Q000235:genetics* / Q000378:metabolism*; D009844:Oligosaccharides / Q000096:biosynthesis* / Q000378:metabolism; D016366:Open Reading Frames / Q000235:genetics; D020161:Physical Chromosome Mapping; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
D001789:Blood Group Antigens; D018076:DNA, Complementary; D009844:Oligosaccharides; D012333:RNA, Messenger; C106678:Sd(a) determinant; D017350:N-Acetylgalactosaminyltransferases; C023220:(N-acetylneuraminyl)-galactosylglucosylceramide N-acetylgalactosaminyltransferase