Streptococcus pneumoniae NanC. Structural insights into the specificity and mechanism of a sialidase that produces a sialidase inhibitor
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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 (Asp-315) 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.
Owen , C D , Lukacik , P , Potter , J A , Sleator , O , Taylor , G L & Walsh , M A 2015 , ' Streptococcus pneumoniae NanC. Structural insights into the specificity and mechanism of a sialidase that produces a sialidase inhibitor ' Journal of Biological Chemistry , vol 290 , no. 46 , pp. 27736-27748 . DOI: 10.1074/jbc.M115.673632
Journal of Biological Chemistry
© 2015 by The American Society for Biochemistry and Molecular Biology, Inc. Author’s Choice—Final version free via Creative Commons CC-BY license.
This work was supported by the Biotechnology and Biological Sciences Research Council (UK) and the Medical Research Council (UK).
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