Identification and characterization of three novel β1,3-N-acetylglucosaminyltransferases structurally related to the β1,3-galactosyltransferase family

We have isolated three types of cDNAs encoding novel beta1,3-N-acetylglucosaminyltransferases (designated beta 3Gn-T2, -T3, and -T4) from human gastric mucosa and the neuroblastoma cell Line SK-N-MC, These enzymes are predicted to be type 2 transmembrane proteins of 397, 372, and 378 amino acids, respectively, They share motifs conserved among members of the beta1,3-galactosyltransferase family and a beta1,3-N-acetylglucosaminyltransferase (designated beta 3Gn-T1), but show no structural similarity to another type of pl,3-N-acetylglucosaminyltransferase (iGnT). Each of the enzymes expressed by insect cells as a secreted protein fused to the FLAG peptide showed beta1,3N-acetylglucosaminyltransferase activity for type 2 oligosaccharides but not pl,3-galactosyltransferase activity. These enzymes exhibited different substrate specificity. Transfection of Namalwa KJM-1 cells with beta 3Gn-T2, -T3, or -T4 cDNA led to an increase in poly-N-acetyllactosamines recognized by an anti-i-antigen antibody or specific lectins, The expression profiles of these beta 3Gn-Ts were different among 35 human tissues, beta 3Gn-T2 was ubiquitously expressed, whereas expression of beta 3Gn-T3 and -T4 was relatively restricted. beta 3Gn-T3 was expressed in colon, jejunum, stomach, esophagus, placenta, and trachea beta 3Gn-T4 was mainly expressed in brain. These results have revealed that several beta1,3-N-acetylglucosaminyltransferases form a family with structural similarity to the pl,3-galactosyltransferase family. Considering the differences in substrate specificity and distribution, each pl,3-N-acetylglucosaminyltransferase may play different roles,