J Biol Chem. 2015 Sep 14. pii: jbc.M115.673632. [Epub ahead of print]

Streptococcus pneumoniae NanC: Structural Insights into the Specificity and Mechanism of a Sialidase that Produces a Sialidase Inhibitor.

Owen CD1, Lukacik P2, Potter JA1, Sleator O3, Taylor GL1, Walsh MA4.

Author information

Abstract

Streptococcus pneumoniae is an important human pathogen that causes a range of disease states. Sialidases are important bacterial virulence factors. There are three pneumococcal sialidases: NanA, NanB and NanC. NanC is an unusual sialidase in that its primary reaction product is 2-deoxy-2,3-didehydro-N-acetylneuraminic acid (Neu5Ac2en, also known as DANA) a nonspecific hydrolytic sialidase inhibitor. The production of Neu5Ac2en from α2-3 linked sialosides by the catalytic domain is confirmed within a crystal structure. A covalent complex with 3-fluoro-β-N-acetylneuraminic acid is also presented, suggesting a common mechanism with other sialidases up to the final step of product formation. A conformation change in an active site hydrophobic loop on ligand binding constricts the entrance to the active site. In addition, the distance between the catalytic acid/base (Asp315) and the ligand anomeric carbon is unusually short. These features facilitate a novel sialidase reaction in which the final step of product formation is direct abstraction of the C3 proton by the active site aspartic acid, forming Neu5Ac2en. NanC also possesses a carbohydrate binding module, which is shown to bind α2-3 and α2-6 linked sialosides as well as N-acetylneuraminic acid, which is captured in the crystal structure following hydration of Neu5Ac2en by NanC. Overall, the pneumococcal sialidases show remarkable mechanistic diversity while maintaining a common structural scaffold.

Copyright © 2015, The American Society for Biochemistry and Molecular Biology.

KEYWORDS:

NanC; Streptococcus; carbohydrate binding module; glycoside hydrolase; neu5ac2en; neuraminidase; pneumococcus; sialic acid; sialidase

PMID: 26370075 [PubMed - as supplied by publisher]

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