期刊
JOURNAL OF BIOLOGICAL CHEMISTRY
卷 284, 期 26, 页码 17404-17410出版社
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M109.003970
关键词
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资金
- Leverhulme Trust
- Natural Sciences and Engineering Research Council
- Canada Research Chairs
- Canadian Institute of Health Research
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 H-1 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.
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