title: Topology and Structure/Function Correlation of Ring- and Gate-forming Domains in the Dynamic Secretin Complex of Thermus thermophilus.
abstract: Secretins are versatile outer membrane pores used by many bacteria to secrete proteins, toxins, or filamentous phages; extrude type IV pili (T4P); or take up DNA. Extrusion of T4P and natural transformation of DNA in the thermophilic bacterium Thermus thermophilus requires a unique secretin complex comprising six stacked rings, a membrane-embedded cone structure, and two gates that open and close a central channel. To investigate the role of distinct domains in ring and gate formation, we examined a set of deletion derivatives by cryomicroscopy techniques. Here we report that maintaining the N0 ring in the deletion derivatives led to stable PilQ complexes. Analyses of the variants unraveled that an N-terminal domain comprising a unique βββαβ fold is essential for the formation of gate 2. Furthermore, we identified four βαββα domains essential for the formation of the N2 to N5 rings. Mutant studies revealed that deletion of individual ring domains significantly reduces piliation. The N1, N2, N4, and N5 deletion mutants were significantly impaired in T4P-mediated twitching motility, whereas the motility of the N3 mutant was comparable with that of wild-type cells. This indicates that the deletion of the N3 ring leads to increased pilus dynamics, thereby compensating for the reduced number of pili of the N3 mutant. All mutants exhibit a wild-type natural transformation phenotype, leading to the conclusion that DNA uptake is independent of functional T4P.
authors.affiliation: From Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Goethe University Frankfurt, 60438 Frankfurt am Main and.
authors.forename: Ralf
authors.initials: R
authors.lastname: Salzer
authors.affiliation: the Department of Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany.
authors.forename: Edoardo
authors.initials: E
authors.lastname: D'Imprima
authors.affiliation: the Department of Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany.
authors.forename: Vicki A M
authors.initials: VA
authors.lastname: Gold
authors.affiliation: From Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Goethe University Frankfurt, 60438 Frankfurt am Main and.
authors.forename: Ilona
authors.initials: I
authors.lastname: Rose
authors.affiliation: From Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Goethe University Frankfurt, 60438 Frankfurt am Main and.
authors.forename: Moritz
authors.initials: M
authors.lastname: Drechsler
authors.affiliation: the Department of Structural Biology, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany.
authors.forename: Janet
authors.initials: J
authors.lastname: Vonck
authors.affiliation: From Molecular Microbiology and Bioenergetics, Institute of Molecular Biosciences, Goethe University Frankfurt, 60438 Frankfurt am Main and averhoff@bio.uni-frankfurt.de.
authors.forename: Beate
authors.initials: B
authors.lastname: Averhoff
mesh_terms: D015640:Ion Channel Gating; D011487:Protein Conformation; D012633:Secretin / Q000737:chemistry / Q000378:metabolism*; D013329:Structure-Activity Relationship; D016963:Thermus thermophilus / Q000737:chemistry / Q000378:metabolism*
chemical_list: D012633:Secretin
keywords: EM; Thermus thermophilus; electron cryotomography; natural transformation; protein domain; protein folding; ring and gate forming domains; secretin; structure/function; type IV pili