Mutated PglB oligosaccharyl transferase enzymes

An engineered PglB oligosaccharyltransferase (OST) polypeptide comprising an amino acid sequence that is at least 90%, 95%, 96%, 97%, 98%, or 99% identical to the amino acid sequence of SEQ ID NO:

• 1 or SEQ ID NO:
• 2 wherein the engineered PglB OST polypeptide comprises a substitution at the amino acid residue corresponding to the amino acid at position 57 of the amino acid sequence of SEQ ID NO:
• 1, wherein said substitution is to R, K or T and
• at least one substitution at an amino acid residue at a position selected from the group consisting of R63, Y77, Y78, A84, P94, 1101, M155, I172, D176, L191, W193, L233, S234, Q255, Y286, F293, S295, N300, L301, M306, F308, N311, N319, V397, Q402, Y425, Q435, N446, Y462, V464, H479, T523, D532, D601, G605, E606, S610, Y645, K676, and N695, wherein said position(s) correspond to the amino acid sequence of SEQ ID NO:1, and
• wherein the engineered PglB OST polypeptide increases the yield of glycosylation of a protein with a saccharide by at least 1.5 fold compared to a corresponding PglB OST polypeptide comprising the amino acid sequence of SEQ ID NO:1.