title: The Vibrio cholerae Minor Pilin TcpB Initiates Assembly and Retraction of the Toxin-Coregulated Pilus.
abstract: Type IV pilus (T4P) systems are complex molecular machines that polymerize major pilin proteins into thin filaments displayed on bacterial surfaces. Pilus functions require rapid extension and depolymerization of the pilus, powered by the assembly and retraction ATPases, respectively. A set of low abundance minor pilins influences pilus dynamics by unknown mechanisms. The Vibrio cholerae toxin-coregulated pilus (TCP) is among the simplest of the T4P systems, having a single minor pilin TcpB and lacking a retraction ATPase. Here we show that TcpB, like its homolog CofB, initiates pilus assembly. TcpB co-localizes with the pili but at extremely low levels, equivalent to one subunit per pilus. We used a micropillars assay to demonstrate that TCP are retractile despite the absence of a retraction ATPase, and that retraction relies on TcpB, as a V. cholerae tcpB Glu5Val mutant is fully piliated but does not induce micropillars movements. This mutant is impaired in TCP-mediated autoagglutination and TcpF secretion, consistent with retraction being required for these functions. We propose that TcpB initiates pilus retraction by incorporating into the growing pilus in a Glu5-dependent manner, which stalls assembly and triggers processive disassembly. These results provide a framework for understanding filament dynamics in more complex T4P systems and the closely related Type II secretion system.
authors.affiliation: Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada.
authors.forename: Dixon
authors.identifier: http://orcid.org/0000-0002-8615-1787
authors.initials: D
authors.lastname: Ng
authors.affiliation: Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada.
authors.forename: Tony
authors.initials: T
authors.lastname: Harn
authors.affiliation: Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada.
authors.forename: Tuba
authors.identifier: http://orcid.org/0000-0002-2979-4129
authors.initials: T
authors.lastname: Altindal
authors.affiliation: Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada.
authors.forename: Subramania
authors.identifier: http://orcid.org/0000-0001-7469-2298
authors.initials: S
authors.lastname: Kolappan
authors.affiliation: Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, United States of America.
authors.forename: Jarrad M
authors.identifier: http://orcid.org/0000-0002-6923-058X
authors.initials: JM
authors.lastname: Marles
authors.affiliation: Biology Department, Brooklyn College, City University of New York, Brooklyn, New York, United States of America.
authors.forename: Rajan
authors.identifier: http://orcid.org/0000-0002-4870-5929
authors.initials: R
authors.lastname: Lala
authors.affiliation: Biology Department, Brooklyn College, City University of New York, Brooklyn, New York, United States of America.
authors.forename: Ingrid
authors.initials: I
authors.lastname: Spielman
authors.affiliation: Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, United States of America.
authors.forename: Yang
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, United States of America.
authors.forename: Caitlyn A
authors.identifier: http://orcid.org/0000-0003-0940-547X
authors.initials: CA
authors.lastname: Hauke
authors.affiliation: Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, United States of America.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Kovacikova
authors.affiliation: Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada.
authors.forename: Zia
authors.identifier: http://orcid.org/0000-0002-1017-5774
authors.initials: Z
authors.lastname: Verjee
authors.affiliation: Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, United States of America.
authors.forename: Ronald K
authors.initials: RK
authors.lastname: Taylor
authors.affiliation: Biology Department, Brooklyn College, City University of New York, Brooklyn, New York, United States of America.|Graduate Center, City University of New York, Brooklyn, New York, United States of America.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Biais
authors.affiliation: Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada.
authors.forename: Lisa
authors.identifier: http://orcid.org/0000-0001-8515-9915
authors.initials: L
authors.lastname: Craig
mesh_terms: D036781:Fimbriae Proteins / Q000378:metabolism*; D010861:Fimbriae, Bacterial / Q000378:metabolism* / Q000648:ultrastructure; D015151:Immunoblotting; D007150:Immunohistochemistry; D046529:Microscopy, Electron, Transmission; D014734:Vibrio cholerae / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: C099205:TcpB protein, Vibrio cholerae; D036781:Fimbriae Proteins