Molecular cloning and characterization of a novel UDP-Gal:GaINAcα peptide β1,3-galactosyltransferase (ClGal-T2), an enzyme synthesizing a core 1 structure of O-glycan

Recently, a UDP-Gal:GalNAcalpha peptide beta1,3-galactosyltransferase (core 1 synthase 1; C1Gal-T1) has been purified from rat liver and its complementary DNA cloned from several species. We isolated a second candidate for core 1 synthase from a Colo205 cDNA library and named it C1Gal-T2. The deduced amino acid sequence of C1Gal-T2, having 26% homology to C1Gal-T1, showed a topology typical of a type II membrane protein. Real time PCR analysis revealed that the expression of C1Gal-T2 transcripts was widespread in many tissues and of relatively high level in salivary gland, stomach, small intestine, kidney, testis, thymus, and spleen. LSC cells, having no core 1 synthase activity, were transfected stably with the C1Gal-T2 gene. Their microsome fraction showed beta1,3-galactosyltransferase activity toward GalNAc-alpha-para-nitrophenyl and GalNAcalpha1 peptides resulting in the synthesis of the core 1 structure. The core 1 synthesizing activity of C1Gal-T2 was also determined by flow cytometry and lectin blotting using the LSC cells stably expressing C1Gal-T2. Finally, LSC cells, and Jurkat cells that also lack the core 1 synthase activity, were found to have null alleles of C1Gal-T2. These results indicated that C1Gal-T2 is the second candidate for core 1 synthase that plays an important role in synthesizing O-glycans in digestive organs.