Molecular cloning, gene organization and expression of the human UDP-GalNAc:Neu5Acalpha2-3Galbeta-R beta1,4-N-acetylgalactosaminyltransferase responsible for the biosynthesis of the blood group Sda/Cad antigen: evidence for an unusual extended cytoplasmic domain

Abstract

The nucleotide sequence of the short and long transcripts of beta1,4- N -acetylgalactosaminyltransferase have been submitted to the DDBJ, EMBL, GenBank(R) and GSDB Nucleotide Sequence Databases under accession nos AJ517770 and AJ517771 respectively. The human Sd(a) antigen is formed through the addition of an N -acetylgalactosamine residue via a beta1,4-linkage to a sub-terminal galactose residue substituted with an alpha2,3-linked sialic acid residue. We have taken advantage of the previously cloned mouse cDNA sequence of the UDP-GalNAc:Neu5Acalpha2-3Galbeta-R beta1,4- N -acetylgalactosaminyltransferase (Sd(a) beta1,4GalNAc transferase) to screen the human EST and genomic databases and to identify the corresponding human gene. The sequence spans over 35 kb of genomic DNA on chromosome 17 and comprises at least 12 exons. As judged by reverse transcription PCR, the human gene is expressed widely since it is detected in various amounts in almost all cell types studied. Northern blot analysis indicated that five Sd(a) beta1,4GalNAc transferase transcripts of 8.8, 6.1, 4.7, 3.8 and 1.65 kb were highly expressed in colon and to a lesser extent in kidney, stomach, ileum and rectum. The complete coding nucleotide sequence was amplified from Caco-2 cells. Interestingly, the alternative use of two first exons, named E1(S) and E1(L), leads to the production of two transcripts. These nucleotide sequences give rise potentially to two proteins of 506 and 566 amino acid residues, identical in their sequence with the exception of their cytoplasmic tail. The short form is highly similar (74% identity) to the mouse enzyme whereas the long form shows an unusual long cytoplasmic tail of 66 amino acid residues that is as yet not described for any other mammalian glycosyltransferase. Upon transient transfection in Cos-7 cells of the common catalytic domain, a soluble form of the protein was obtained, which catalysed the transfer of GalNAc residues to alpha2,3-sialylated acceptor substrates, to form the GalNAcbeta1-4[Neu5Acalpha2-3]Galbeta1-R trisaccharide common to both Sd(a) and Cad antigens.

Identification of New Carbohydrate and Membrane Protein Antigens in Cardiac Xenotransplantation

“…In humans and mice, the B4GALNT2 enzyme catalyzes the ␤1-4 addition of N-acetylgalactosamine (GalNAc) to terminal ␣2-3 sialylated Gal residues to produce the SD a antigen (also known as CAD) (26,27). This carbohydrate structure is most abundant on the Tamm-Horsfall urinary glycoprotein.…”

Selectin Ligands Sialyl-Lewis a and Sialyl-Lewis x in Gastrointestinal Cancers

“…In a recent review [20], we have proposed that the right question to answer is not “why are sLe x levels high in colon cancer?” but rather “why are sLe x levels low in the normal colon?” Competition between FUT6 and enzymes synthesizing alternative structures, such as Siaα2,3(GalNAcβ1,4)Galβ1,3/4GlcNAc (the Sd a antigen) [21,22] or the sialyl 6-sulfo-Lewis x antigen [23] has been proposed. The Sd a antigen is the product of β1,4 N -acetylgalactosaminyltransferase-II (B4GALNT2) [24,25]. Both the Sd a antigen and B4GALNT2 are highly expressed in normal colon and down-regulated in colon cancer [26,27].…”

Copy number variation and evolution in humans and chimpanzees

“…Fig. 2) (results from the third CNV were inconclusive), including one that encompassed the promoter region and first exon of the B4GALNT2 gene, whose product is required for synthesis of the Sda and CAD antigens in human erythrocytes and colon mucins (Montiel et al 2003). In this way, distinguishing among fixed and polymorphic deletions at sequence gap locations-which has implications for evolutionary analyses of patterns of gene gain and loss in primates (Hahn et al 2007)-and identifying individuals for subsequent recovery of missing sequences is practicable for chimpanzees.…”