title: Crystal Structure of Hcp from Acinetobacter baumannii: A Component of the Type VI Secretion System.
abstract: The type VI secretion system (T6SS) is a bacterial macromolecular machine widely distributed in Gram-negative bacteria, which transports effector proteins into eukaryotic host cells or other bacteria. Membrane complexes and a central tubular structure, which resembles the tail of contractile bacteriophages, compose the T6SS. One of the proteins forming this tube is the hemolysin co-regulated protein (Hcp), which acts as virulence factor, as transporter of effectors and as a chaperone. In this study, we present the structure of Hcp from Acinetobacter baumannii, together with functional and oligomerization studies. The structure of this protein exhibits a tight β barrel formed by two β sheets and flanked at one side by a short α-helix. Six Hcp molecules associate to form a donut-shaped hexamer, as observed in both the crystal structure and solution. These results emphasize the importance of this oligomerization state in this family of proteins, despite the low similarity of sequence among them. The structure presented in this study is the first one for a protein forming part of a functional T6SS from A. baumannii. These results will help us to understand the mechanism and function of this secretion system in this opportunistic nosocomial pathogen.
authors.affiliation: Department of Chemical and Physical Biology, Centro de Investigaciones Biológicas-CSIC, Madrid, Spain.
authors.forename: Federico M
authors.initials: FM
authors.lastname: Ruiz
authors.affiliation: Department of Chemical and Physical Biology, Centro de Investigaciones Biológicas-CSIC, Madrid, Spain.
authors.forename: Elena
authors.initials: E
authors.lastname: Santillana
authors.affiliation: Department of Chemical and Physical Biology, Centro de Investigaciones Biológicas-CSIC, Madrid, Spain.
authors.forename: Mercedes
authors.initials: M
authors.lastname: Spínola-Amilibia
authors.affiliation: Department of Chemical and Physical Biology, Centro de Investigaciones Biológicas-CSIC, Madrid, Spain.
authors.forename: Eva
authors.initials: E
authors.lastname: Torreira
authors.affiliation: Department of Clinical Microbiology, Hospital Clínico San Carlos, Madrid, Spain.
authors.forename: Esther
authors.initials: E
authors.lastname: Culebras
authors.affiliation: Department of Chemical and Physical Biology, Centro de Investigaciones Biológicas-CSIC, Madrid, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Romero
mesh_terms: D040981:Acinetobacter baumannii; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D000069376:Type VI Secretion Systems / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D000069376:Type VI Secretion Systems