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 β1,3-N-acetylglucosaminyltransferases (designated β3Gn-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 β1,3-galactosyltransferase family and a β1,3-N-acetylglucosaminyltransferase (designated β3Gn-T1), but show no structural similarity to another type of β1,3-N-acetylglucosaminyltransferase (iGnT). Each of the enzymes expressed by insect cells as a secreted protein fused to the FLAG peptide showed β1,3-N-acetylglucosaminyltransferase activity for type 2 oligosaccharides but not β1,3-galactosyltransferase activity. These enzymes exhibited different substrate specificity. Transfection of Namalwa KJM-1 cells with β3Gn-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 β3Gn-Ts were different among 35 human tissues. β3Gn-T2 was ubiquitously expressed, whereas expression of β3Gn-T3 and -T4 was relatively restricted. β3Gn-T3 was expressed in colon, jejunum, stomach, esophagus, placenta, and trachea. β3Gn-T4 was mainly expressed in brain. These results have revealed that several β1,3-N-acetylglucosaminyltransferases form a family with structural similarity to the β1,3-galactosyltransferase family. Considering the differences in substrate specificity and distribution, each β1,3-N-acetylglucosaminyltransferase may play different roles.