title: Streptococcus pneumoniae NanC: STRUCTURAL INSIGHTS INTO THE SPECIFICITY AND MECHANISM OF A SIALIDASE THAT PRODUCES A SIALIDASE INHIBITOR.
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 (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.
authors.affiliation: From the Biomedical Sciences Research Complex, University of St. Andrews, St. Andrews, Fife KY16 9ST, United Kingdom.
authors.forename: C David
authors.initials: CD
authors.lastname: Owen
authors.affiliation: Diamond Light Source and Research Complex at Harwell, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0FA, United Kingdom, and.
authors.forename: Petra
authors.initials: P
authors.lastname: Lukacik
authors.affiliation: From the Biomedical Sciences Research Complex, University of St. Andrews, St. Andrews, Fife KY16 9ST, United Kingdom.
authors.forename: Jane A
authors.initials: JA
authors.lastname: Potter
authors.affiliation: the Medical Research Council France, c/o European Synchrotron Radiation Facility, BP 220, 38043 Grenoble, France.
authors.forename: Olivia
authors.initials: O
authors.lastname: Sleator
authors.affiliation: From the Biomedical Sciences Research Complex, University of St. Andrews, St. Andrews, Fife KY16 9ST, United Kingdom, glt2@st-andrews.ac.uk.
authors.forename: Garry L
authors.initials: GL
authors.lastname: Taylor
authors.affiliation: Diamond Light Source and the Medical Research Council France, c/o European Synchrotron Radiation Facility, BP 220, 38043 Grenoble, France martin.walsh@diamond.ac.uk.
authors.forename: Martin A
authors.initials: MA
authors.lastname: Walsh
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000648:ultrastructure; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000138:chemical synthesis*; D009439:Neuraminidase / Q000737:chemistry* / Q000648:ultrastructure; D013296:Streptococcus pneumoniae / Q000201:enzymology*; D013400:Sugar Acids / Q000138:chemical synthesis*
chemical_list: C577845:5-acetamido-2,6-anhydro-2,3-dehydro-3,5-dideoxy-glycerogalactononanoic acid; D001426:Bacterial Proteins; D004791:Enzyme Inhibitors; D013400:Sugar Acids; D009439:Neuraminidase
keywords: NanC; Streptococcus; carbohydrate-binding module; glycoside hydrolase; neu5ac2en; neuraminidase; pneumococcus; sialic acid; sialidase