title: Extended loop region of Hcp1 is critical for the assembly and function of type VI secretion system in Burkholderia pseudomallei.
abstract: The Type VI Secretion System cluster 1 (T6SS1) is essential for the pathogenesis of Burkholderia pseudomallei, the causative agent of melioidosis, a disease endemic in the tropics. Inside host cells, B. pseudomallei escapes into the cytosol and through T6SS1, induces multinucleated giant cell (MNGC) formation that is thought to be important for bacterial cell to cell spread. The hemolysin-coregulated protein (Hcp) is both a T6SS substrate, as well as postulated to form part of the T6SS secretion tube. Our structural study reveals that Hcp1 forms hexameric rings similar to the other Hcp homologs but has an extended loop (Asp40-Arg56) that deviates significantly in position compared to other Hcp structures and may act as a key contact point between adjacent hexameric rings. When two residues within the loop were mutated, the mutant proteins were unable to stack as dodecamers, suggesting defective tube assembly. Moreover, infection with a bacterial mutant containing in situ substitution of these hcp1 residues abolishes Hcp1 secretion inside infected cells and MNGC formation. We further show that Hcp has the ability to preferentially bind to the surface of antigen-presenting cells, which may contribute to its immunogenicity in inducing high titers of antibodies seen in melioidosis patients.
authors: 1] Department of Microbiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore [2] NUS Graduate School of Integrative Sciences and Engineering, National University of Singapore, Singapore [3] Life Sciences Institute, Immunology Program, National University of Singapore, Singapore.
authors: Yan Ting
authors: YT
authors: Lim
authors: Department of Biological Sciences, National University of Singapore, Singapore.
authors: Chacko
authors: C
authors: Jobichen
authors: 1] Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore [2] NUS Graduate School of Integrative Sciences and Engineering, National University of Singapore, Singapore.
authors: Jocelyn
authors: J
authors: Wong
authors: Department of Tropical Hygiene and Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
authors: Direk
authors: D
authors: Limmathurotsakul
authors: National Institute of Diagnostics and Vaccine Development in Infectious Diseases, School of Life Sciences, Xiamen University, Xiamen, China.
authors: Shaowei
authors: S
authors: Li
authors: Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
authors: Yahua
authors: Y
authors: Chen
authors: Life Sciences Institute, Singapore Lipidomics Incubator, National University of Singapore, Singapore.
authors: Manfred
authors: M
authors: Raida
authors: Department of Microbiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
authors: Nalini
authors: N
authors: Srinivasan
authors: 1] Department of Microbiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore [2] Life Sciences Institute, Immunology Program, National University of Singapore, Singapore.
authors: Paul Anthony
authors: PA
authors: MacAry
authors: Department of Biological Sciences, National University of Singapore, Singapore.
authors: J
authors: J
authors: Sivaraman
authors: Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
authors: Yunn-Hwen
authors: YH
authors: Gan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000907:Antibodies, Bacterial / Q000276:immunology; D000938:Antigen-Presenting Cells / Q000378:metabolism; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D016957:Burkholderia pseudomallei / Q000502:physiology*; D002460:Cell Line; D006801:Humans; D008264:Macrophages / Q000276:immunology / Q000378:metabolism; D008554:Melioidosis / Q000276:immunology / Q000382:microbiology; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D011994:Recombinant Proteins / Q000378:metabolism; D000069376:Type VI Secretion Systems
chemical_list: D000907:Antibodies, Bacterial; D001425:Bacterial Outer Membrane Proteins; D011994:Recombinant Proteins; D000069376:Type VI Secretion Systems
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