Distinct expression profiles of UDP-galactose: beta-D-galactoside alpha1,4-galactosyltransferase and UDP-galactose: beta-D-galactoside beta1,4-galactosyltransferase in pigeon, ostrich and chicken.

摘要

We previously identified two novel enzymes in pigeon, alpha1,4- and beta1,4-galactosyltransferases (GalTs), which are responsible for the biosynthesis of the Galalpha1-4Gal and Galbeta1-4Gal sequences on glycoproteins, respectively. No such glycan structures and/or enzymes have been found in mammals, suggesting that the expression of these enzymes diverged during the course of vertebrate evolution. To compare their expression profiles among avian species, we first established a method for detecting the activities of these two GalTs based on the two-dimensional high pressure liquid chromatography mapping technique, using 2-aminopyridine-derivatized asialo-biantennary N-glycans as an acceptor substrate. When we analyzed the activities of GalTs in pigeon liver extracts in the presence of UDP-Gal, 13 different products containing Galalpha1-4Galbeta1-4GlcNAc, Galbeta1-4Galbeta1-4GlcNAc and/or Galalpha1-4Galbeta1-4Galbeta1-4GlcNAc branches were identified. The newly formed glycosidic linkages of the enzymatic products were determined by nuclear magnetic resonance and methylation analysis, as well as by galactosidase digestions. The activities of both alpha1,4- and beta1,4-GalTs were detected in various tissues in pigeon, although their relative activities were different in each tissue. In contrast, ostrich expressed beta1,4-GalT, but not alpha1,4-GalT, in all tissues analyzed, whereas neither alpha1,4- nor beta1,4-GalT activity was detected in chicken. These results indicate that alpha1,4- and beta1,4-GalTs are expressed in a species-specific manner and are distributed throughout the entire body of pigeon or ostrich when the enzymes are present.