Dolichyl-phosphate-mannose-protein mannosyltransferase. This is a family of Dolichyl-phosphate-mannose-protein mannosyltransferase proteins EC:2.4.1.109. These proteins are responsible for O-linked glycosylation of proteins, they catalyze the reaction:- Dolichyl phosphate D-mannose + protein <=> dolichyl phosphate + O-D-mannosyl-protein. Also in this family is Drosophila rotated abdomen protein which is a putative mannosyltransferase. This family appears to be distantly related to pfam02516 (A Bateman pers. obs.). This family also contains sequences from ArnTs (4-amino-4-deoxy-L-arabinose lipid A transferase). They catalyze the addition of 4-amino-4-deoxy-l-arabinose (l-Ara4N) to the lipid A moiety of the lipopolysaccharide. This is a critical modification enabling bacteria (e.g. Escherichia coli and Salmonella typhimurium) to resist killing by antimicrobial peptides such as polymyxins. Members such as undecaprenyl phosphate-alpha-4-amino-4-deoxy-L-arabinose arabinosyl transferase are predicted to have 12 trans-membrane regions. The N-terminal portion of these proteins is hypothesized to have a conserved glycosylation activity which is shared between distantly related oligosaccharyltransferases ArnT and PglB families.
Oligosaccharyl transferase STT3 subunit. This family consists of the oligosaccharyl transferase STT3 subunit and related proteins. The STT3 subunit is part of the oligosaccharyl transferase (OTase) complex of proteins and is required for its activity. In eukaryotes, OTase transfers a lipid-linked core-oligosaccharide to selected asparagine residues in the ER. In the archaea STT3 occurs alone, rather than in an OTase complex, and is required for N-glycosylation of asparagines.