title: Crystal structure of the type IV secretion system component CagX from Helicobacter pylori.
abstract: Helicobacter pylori, a Gram-negative bacterial pathogen prevalent in the human population, is the causative agent of severe gastric diseases. An H. pylori type IV secretion (T4S) system encoded by the cytotoxin-associated gene pathogenicity island (cagPAI) is responsible for communication with host cells. As a component of the cagPAI T4S system core complex, CagX plays an important role in virulence-protein translocation into the host cells. In this work, the crystal structure of the C-terminal domain of CagX (CagXct), which is a homologue of the VirB9 protein from the VirB/D4 T4S system, is presented. CagXct is only the second three-dimensional structure to be elucidated of a VirB9-like protein. Another homologue, TraO, which is encoded on the Escherichia coli conjugative plasmid pKM101, shares only 19% sequence identity with CagXct; however, there is a remarkable similarity in tertiary structure between these two β-sandwich protein domains. Most of the residues that are conserved between CagXct and TraO are located within the protein core and appear to be responsible for the preservation of this domain fold. The studies presented here will contribute to our understanding of different bacterial T4S systems.
authors.affiliation: State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Science, Fuzhou 350002, People's Republic of China.
authors.forename: Jin
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Fujian Health College, Fuzhou 350101, People's Republic of China.
authors.forename: Fei
authors.initials: F
authors.lastname: Fan
authors.affiliation: State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Science, Fuzhou 350002, People's Republic of China.
authors.forename: Yanhe
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Science, Fuzhou 350002, People's Republic of China.
authors.forename: Lifang
authors.initials: L
authors.lastname: Sun
authors.affiliation: State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Science, Fuzhou 350002, People's Republic of China.
authors.forename: Yadan
authors.initials: Y
authors.lastname: Liu
authors.affiliation: CCP4, Research Complex at Harwell, Rutherford Appleton Laboratory, Harwell Oxford, Didcot OX11 0FA, England.
authors.forename: Ronan M
authors.initials: RM
authors.lastname: Keegan
authors.affiliation: The Henry Wellcome Building for Biocatalysis, Biosciences, College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4QD, England.
authors.forename: Michail N
authors.initials: MN
authors.lastname: Isupov
authors.affiliation: State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Science, Fuzhou 350002, People's Republic of China.
authors.forename: Yunkun
authors.initials: Y
authors.lastname: Wu
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D044404:Genomic Islands; D016480:Helicobacter pylori / Q000737:chemistry* / Q000378:metabolism / Q000472:pathogenicity; D008958:Models, Molecular; D010957:Plasmids / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D000072757:Protein Conformation, beta-Strand; D017510:Protein Folding; D054730:Protein Interaction Domains and Motifs; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D040681:Structural Homology, Protein; D000069319:Type IV Secretion Systems / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D037521:Virulence Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D011994:Recombinant Proteins; C521591:TraO protein, E coli; D000069319:Type IV Secretion Systems; D037521:Virulence Factors
keywords: CagX; Helicobacter pylori; X-ray diffraction; cagPAI; crystal structure; cytotoxin-associated gene pathogenicity island; type IV secretion system