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An α2,3-Sialyltransferase from Photobacterium sp. JT-ISH-224 Transfers N-Acetylneuraminic Acid to Both the O-2 and O-3′ Hydroxyl Groups of Lactose

We found that α2,3-sialyltransferase from Photobacterium sp. JT-ISH-224 produced a regio-mistaken sialyl-transferred by-product. Spectroscopic analysis of the purified by-product indicated that it contained two N-acetylneuraminic acids: one attached to the O-3′ hydroxyl group of lactose, and the other attached to the O-2 hydroxyl group of lactose. The relative configuration between the C-1 and C-3 of the α-glucopyranose residue is superimposable with that between C-4 and C-2 of galactopyranoside. Therefore, formation of this by-product, designated 2,3′-disialyllactose, was simply rationalized as a regio-mistaken reaction of bacterial α2,3-sialyltransferase. This finding indicates that this bacterial α2,3-sialyltransferase has a possibility to synthesize several unusual sialosides.