title: Crystal structure of the polysialic acid-degrading endosialidase of bacteriophage K1F.
abstract: Phages infecting the polysialic acid (polySia)-encapsulated human pathogen Escherichia coli K1 are equipped with capsule-degrading tailspikes known as endosialidases, which are the only identified enzymes that specifically degrade polySia. As polySia also promotes cellular plasticity and tumor metastasis in vertebrates, endosialidases are widely applied in polySia-related neurosciences and cancer research. Here we report the crystal structures of endosialidase NF and its complex with oligomeric sialic acid. The structure NF, which reveals three distinct domains, indicates that the unique polySia specificity evolved from a combination of structural elements characteristic of exosialidases and bacteriophage tailspike proteins. The endosialidase assembles into a catalytic trimer stabilized by a triple beta-helix. Its active site differs markedly from that of exosialidases, indicating an endosialidase-specific substrate-binding mode and catalytic mechanism. Residues essential for endosialidase activity were identified by structure-based mutational analysis.
authors.affiliation: Abteilung Zelluläre Chemie, Zentrum Biochemie, Medizinische Hochschule Hannover, Carl-Neuberg-Str. 1, 30625 Hannover, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Stummeyer
authors.forename: Achim
authors.initials: A
authors.lastname: Dickmanns
authors.forename: Martina
authors.initials: M
authors.lastname: Mühlenhoff
authors.forename: Rita
authors.initials: R
authors.lastname: Gerardy-Schahn
authors.forename: Ralf
authors.initials: R
authors.lastname: Ficner
mesh_terms: D001435:Bacteriophages / Q000201:enzymology* / Q000235:genetics; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009439:Neuraminidase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D012794:Sialic Acids / Q000378:metabolism*
chemical_list: D012794:Sialic Acids; C021319:polysialic acid; C035355:endo-N-acetylneuraminidase; D009439:Neuraminidase