Trans-sialidases catalyze the transfer of a sialic acid from one sialoside to an acceptor to form a new sialoside. α2,3-Trans-sialidase activity was initially discovered in the parasitic protozoan Trypanosoma cruzi, and more recently was found in a multifunctional Pasteurella multocida sialyltransferase PmST1. α2,8-Trans-sialidase activity was also described for a multifunctional Campylobacter jejuni sialyltransferase CstII. We report here the discovery of the α2,6-trans-sialidase activity of a previously reported recombinant truncated bacterial α2,6-sialyltransferase from Photobacterium damsela (Δ15Pd2,6ST). This is the first time that the α2,6-trans-sialidase activity has ever been identified. Kinetic studies indicate that Δ15Pd2,6ST-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 Neu5AcαpNP and LacβMU, α2,6-linked sialoside Neu5Acα2,6LacβMU has been obtained in one-step in high yield using the trans-sialidase activity of Δ15Pd2,6ST. In addition to the α2,6-trans-sialidase activity, Δ15Pd2,6ST also has α2,6-sialidase activity. The multifunctionality is thus a common feature of many bacterial sialyltransferases.
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