A4GalT_like proteins catalyze the addition of galactose or glucose residues to the lipooligosaccharide (LOS) or lipopolysaccharide (LPS) of the bacterial cell surface.
The members of this family of glycosyltransferases catalyze the addition of galactose or glucose residues to the lipooligosaccharide (LOS) or lipopolysaccharide (LPS) of the bacterial cell surface. The enzymes exhibit broad substrate specificities. The known functions found in this family include: Alpha-1,4-galactosyltransferase, LOS-alpha-1,3-D-galactosyltransferase, UDP-glucose:(galactosyl) LPS alpha1,2-glucosyltransferase, UDP-galactose: (glucosyl) LPS alpha1,2-galactosyltransferase, and UDP-glucose:(glucosyl) LPS alpha1,2-glucosyltransferase. Alpha-1,4-galactosyltransferase from N. meningitidis adds an alpha-galactose from UDP-Gal (the donor) to a terminal lactose (the acceptor) of the LOS structure of outer membrane. LOSs are virulence factors that enable the organism to evade the immune system of host cells. In E. coli, the three alpha-1,2-glycosyltransferases, that are involved in the synthesis of the outer core region of the LPS, are all members of this family. The three enzymes share 40 % of sequence identity, but have different sugar donor or acceptor specificities, representing the structural diversity of LPS.