Dissection of hexosyl-and sialyl-transferase domains in the bi-functional capsule polymerases from Neisseria meningitidis W and Y defines a new sialyltransferase family [Glycobiology and Extracellular Matrices]

October 23rd, 2014 by Romanow, A., Keys, T. G., Stummeyer, K., Freiberger, F., Henrissat, B., Gerardy-Schahn, R.

Crucial virulence determinants of disease causing Neisseria meningitidis (Nm) species are their extracellular polysaccharide capsules (CPSs). In the serogroups W and Y these are heteropolymers of the repeating units [→6)-α-D-Gal-(1→4)-α-Neu5Ac-(2→]n in NmW and [→6)-α-D-Glc-(1→4)-α-Neu5Ac-(2→]n in NmY. The capsule polymerases, SiaDW and SiaDY, which synthesise these highly unusual polymers, are composed of two predicted GT-B fold domains separated by a large stretch of amino acids (aa399-762). We recently showed that residues critical to the hexosyl- and sialyltransferase activity are found in the predicted N-terminal (aa1-398) and C-terminal (aa763-1037) GT-B fold domains, respectively. Here we use a mutational approach and synthetic fluorescent substrates to define the boundaries of the hexosyl- and sialyltransferase domains. Our results reveal that the active sialyltransferase domain extends well beyond the predicted C-terminal GT-B domain and defines a new glycosyltransferase family, GT97, in the Carbohydrate Active Enzyme database (CAZy).
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