SEQUENCE OF BOVINE CARBONIC-ANHYDRASE-VI - POTENTIAL RECOGNITION SITES FOR N-ACETYLGALACTOSAMINYLTRANSFERASE

Carbonic anhydrases (CAs I-VII) are products of a gene family that enc odes seven isoenzymes and several CA-related proteins. We report the c loning and sequencing of the cDNA clones encoding one of these isoenzy mes, CA VI, from bovine submaxillary gland. The translated polypeptide consists of 319 amino acids, including a signal peptide (14 amino aci ds) typical of secreted proteins. The predicted mature protein contain s 305 amino acids including a 13-amino-acid C-terminal sequence that i s also present in the sheep but absent in human CA VI. The deduced mat ure bovine protein is 87 % and 68 %, identical to that of sheep and hu man CA VI, respectively. Active-site residues of the enzyme, as well a s the three zinc-binding histidines and the two cysteines involved in an intra-chain disulphide bond, are all conserved in the three species . Two potential Asn-glycosylation sites are also conserved, both of wh ich appear to be glycosylated in sheep and bovine CA VI. Two potential peptide recognition sequences are present in bovine CA VI for the gly coprotein hormone: N-acetylgalactosaminyltransferase (GalNAc-transfera se), which is one of the two transferases required to form GalNAc-4-SO 4 in bovine CA VI-linked oligosaccharides. Specifically, these two seq uences are Asp-Leu-Lys-Met-Lys-Lys and Ile-Thr-Lys-Arg-Lys-Lys. Compar ison of these sequences with sheep and human CA VI sequences indicates that distinct glycoforms of CA VI could exist in submaxillary gland f rom different species.