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Mol Microbiol. 2016 Aug;101(3):457-70. doi: 10.1111/mmi.13403. Epub 2016 May 24.

A novel flagellar sheath protein, FcpA, determines filament coiling, translational motility and virulence for the Leptospira spirochete.

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Department of Epidemiology of Microbial Disease, Yale School of Public Health, New Haven, CT, 06520, USA.
Gonçalo Moniz Research Center, Oswaldo Cruz Foundation, Brazilian Ministry of Health, Salvador, Bahia, 40296-710, Brazil.
Institut Pasteur, Unit of Biology of Spirochetes, 75724 Paris cedex 15, France.
Department of Pathology and Laboratory Medicine, University of Texas Medical School at Houston, Houston, TX, 77030, USA.
Laboratory of Molecular & Structural Microbiology, Institut Pasteur de Montevideo, Montevideo, 11400, Uruguay.
Department of Microbiology and Immunology, West Virginia University, Morgantown, WV, 26506, USA.
Department of Structural Biology and Chemistry, Institute Pasteur, 75724 Paris cedex15, France.


Leptospira are unique among bacteria based on their helical cell morphology with hook-shaped ends and the presence of periplasmic flagella (PF) with pronounced spontaneous supercoiling. The factors that provoke such supercoiling, as well as the role that PF coiling plays in generating the characteristic hook-end cell morphology and motility, have not been elucidated. We have now identified an abundant protein from the pathogen L. interrogans, exposed on the PF surface, and named it Flagellar-coiling protein A (FcpA). The gene encoding FcpA is highly conserved among Leptospira and was not found in other bacteria. fcpA(-) mutants, obtained from clinical isolates or by allelic exchange, had relatively straight, smaller-diameter PF, and were not able to produce translational motility. These mutants lost their ability to cause disease in the standard hamster model of leptospirosis. Complementation of fcpA restored the wild-type morphology, motility and virulence phenotypes. In summary, we identified a novel Leptospira 36-kDa protein, the main component of the spirochete's PF sheath, and a key determinant of the flagella's coiled structure. FcpA is essential for bacterial translational motility and to enable the spirochete to penetrate the host, traverse tissue barriers, disseminate to cause systemic infection and reach target organs.

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