Description
B3GNT8 is a galactosyltransferase involved in the synthesis of poly-N-acetyllactosamine (polyLacNAc), a linear chain of repeating LacNAc units made up of galactose (Gal) and N-acetylglucosamine (GlcNAc) with the structure (Gal-beta-1-4-GlcNAc-beta-1-3)n. By genomic sequence analysis, the B3GNT8 gene is mapped to chromosome 19q13.2. It was showed that a soluble form of B3GNT8 overexpressed by transfected HEK293 cells selectively transferred GlcNAc from UDP-GlcNAc to the nonreducing terminus of Gal-beta-1-4-GlcNAc-alpha-p-nitrophenyl phosphate and to lactoside-alpha-benzoyl. It did not utilize keratan sulfates or polylactosamine oligosaccharide as substrate. B3GNT8 activity required Mn(2+) and showed less efficiency with Co(2+). The pH optimum was between 7 and 7.5. B3GNT8 also transferred GlcNAc onto alpha-1-acid glycoprotein and ovomucoid, which possess tetraantennary complex type and pentaantennary complex type N-glycans. With a tetraantennary N-glycan substrate, B3GNT8 appeared to prefer the beta-1-2 branch over the beta-1-6 branch. When overexpressed in HCT15 human colon cancer cells, B3GNT8 increased cell surface expression of both polyLacNAc and beta-1-6-branched N-glycans