Trans-sialidase activity of Photobacterium damsela α2,6-sialyltransferase and its application in the synthesis of sialosides

Trans-sialidases catalyze the transfer of a sialic acid from one sialoside to an acceptor to form a new sialoside. alpha 2,3-Trans-sialidase activity was initially discovered in the parasitic protozoan Trypanosoma cruzi, and more recently was found in a multifunctional Pasteurella multocida sialyltransferase PmST1. alpha 2,8-Trans-sialidase activity was also described for a multifunctional Campylobacter jejuni sialyltransferase CstII. We report here the discovery of the alpha 2,6-trans-sialidase activity of a previously reported recombinant truncated bacterial alpha 2,6-sialyltransferase from Photobacterium damsela (delta 15Pd2,6ST). This is the first time that the alpha 2,6-trans-sialidase activity has ever been identified. Kinetic studies indicate that delta 15Pd2,6ST-catalyzed trans-sialidase reaction follows a ping-pong bi-bi reaction mechanism. Cytidine 5'-monophosphate, the product of sialyltransferase reactions, is not required by the trans-sialidase activity of the enzyme but enhances the trans-sialidase activity modestly as a non-essential activator. Using chemically synthesized Neu5Ac alpha pNP and Lac beta MU, alpha 2,6-linked sialoside Neu5Ac alpha 2,6Lac beta MU has been obtained in one-step in high yield using the trans-sialidase activity of delta 15Pd2,6ST. In addition to the alpha 2,6-trans-sialidase activity, delta 15Pd2,6ST also has alpha 2,6-sialidase activity. The multifunctionality is thus a common feature of many bacterial sialyltransferases.