A semi-multifunctional sialyltransferase from Bibersteinia trehalosi and its comparison to the Pasteurella multocida ST1 mutants

Sialic acids are well known for their crucial roles in many physiological and pathological processes. Improvement in the efficacy of protein drugs, an increase in the anti-inflammatory activity of intravenous immunoglobulin, preparation of infant milk and the diagnosis of diseases are examples of why there is a need for efficient in vitro sialylation. Sialyltransferases are crucial enzymes for the synthesis of sialo-oligosaccharides. Here, we introduce a new α2,3-sialyltransferase from bacteria Bibersteinia trehalosi (BtST1), which is homological to sialyltransferase from Pasteurella multocida (PmST1), Pasteurella dagmatis (PdST1) and Haemophilus ducreyi (Hd0053). BtST1 is active in a wide pH range and shows considerable acceptor flexibility. Very good specific activities have been detected with lactose and LacNAc as acceptors, and these activities were comparable to those of efficient multifunctional PmST1 and higher than PdST1, Hd0053 and also PmST1 M144D which was constructed to decrease the high sialidase activity of PmST1. Testing of PmST1 mutant forms revealed that mutations that included S143 caused only the restriction of sialyltransferase activity, whereas mutations including G142 resulted in the loss of activity with lactose. BtST1 possesses only low sialidase and trans-sialidase activities that are comparable to mutant PmST1 M144D, which are detected only in the presence of CMP. The combination of large acceptor flexibility, high activity for lactose and LacNAc and naturally low sialidase activity make BtST1 an attractive enzyme for biotechnological applications.