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A New Sialidase Mechanism BACTERIOPHAGE K1F ENDO-SIALIDASE IS AN INVERTING GLYCOSIDASE

TitleA New Sialidase Mechanism BACTERIOPHAGE K1F ENDO-SIALIDASE IS AN INVERTING GLYCOSIDASE
Publication TypeJournal Article
Year of Publication2009
AuthorsMorley, TJ, Willis, LM, Whitfield, C, Wakarchuk, WW, Withers, SG
JournalJOURNAL OF BIOLOGICAL CHEMISTRY
Volume284
Pagination17404-17410
Date PublishedJUN 26
ISSN0021-9258
Abstract

Bacteriophages specific for Escherichia coli K1 express a tailspike protein that degrades the polysialic acid coat of E. coli K1 that is essential for bacteriophage infection. This enzyme is specific for polysialic acid and is a member of a family of endo-sialidases. This family is unusual because all other previously reported sialidases outside of this family are exo- or trans-sialidases. The recently determined structure of an endo-sialidase derived from bacteriophage K1F (endoNF) revealed an active site that lacks a number of the residues that are conserved in other sialidases, implying a new, endo-sialidase-specific catalytic mechanism. Using synthetic trifluoromethylumbelliferyl oligosialoside substrates, kinetic parameters for hydrolysis at a single cleavage site were determined. Measurement of k(cat)/K(m) at a series of pH values revealed a dependence on a single protonated group of pK(a) 5. Mutation of a putative active site acidic residue, E581A, resulted in complete loss of sialidase activity. Direct (1)H NMR analysis of the hydrolysis of trifluoromethylumbelliferyl sialotrioside revealed that endoNF is an inverting sialidase. All other wild type sialidases previously reported are retaining glycosidases, implying a new mechanism of sialidase action specific to this family of endo-sialidases.

DOI10.1074/jbc.M109.003970