title: Processing and maturation of the pilin of the type IV secretion system encoded within the gonococcal genetic island.
abstract: The type IV secretion system (T4SS) encoded within the gonococcal genetic island (GGI) of Neisseria gonorrhoeae has homology to the T4SS encoded on the F plasmid. The GGI encodes the putative pilin protein TraA and a serine protease TrbI, which is homologous to the TraF protein of the RP4 plasmid involved in circularization of pilin subunits of P-type pili. TraA was processed to a 68-amino acid long circular peptide by leader peptidase and TrbI. Processing occurred after co-translational membrane insertion and was independent of other proteins. Circularization occurred after removal of three C-terminal amino acids. Mutational analysis of TraA revealed limited flexibility at the cleavage and joining sites. Mutagenesis of TrbI showed that the conserved Lys-93 and Asp-155 are essential, whereas mutagenesis of Ser-52, the putative catalytic serine did not influence circularization. Further mutagenesis of other serine residues did not identify a catalytic serine, indicating that TrbI either contains redundant catalytic serine residues or does not function via a serine-lysine dyad mechanism. In vitro studies revealed that circularization occurs via a covalent intermediate between the C terminus of TraA and TrbI. The intermediate is processed to the circular form after cleavage of the N-terminal signal sequence. This is the first demonstration of a covalent intermediate in the circularization mechanism of conjugative pili.
authors: Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute and the Zernike Institute for Advanced Materials, University of Groningen, Nijenborg 7, 9747 AG Groningen, The Netherlands; Department of Ecophysiology, Max-Planck-Institute for Terrestrial Microbiology, Karl-von-Frisch-Str., 35043 Marburg, Germany.
authors: Samta
authors: S
authors: Jain
authors: Department of Ecophysiology, Max-Planck-Institute for Terrestrial Microbiology, Karl-von-Frisch-Str., 35043 Marburg, Germany.
authors: Jörg
authors: J
authors: Kahnt
authors: Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute and the Zernike Institute for Advanced Materials, University of Groningen, Nijenborg 7, 9747 AG Groningen, The Netherlands; Department of Ecophysiology, Max-Planck-Institute for Terrestrial Microbiology, Karl-von-Frisch-Str., 35043 Marburg, Germany. Electronic address: does@mpi-marburg.mpg.de.
authors: Chris
authors: C
authors: van der Does
mesh_terms: D004252:DNA Mutational Analysis; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry; D036781:Fimbriae Proteins / Q000737:chemistry*; D013058:Mass Spectrometry / Q000379:methods; D008565:Membrane Proteins / Q000737:chemistry; D008957:Models, Genetic; D009154:Mutation; D009344:Neisseria gonorrhoeae / Q000235:genetics / Q000378:metabolism*; D018933:Pili, Sex / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012697:Serine Endopeptidases / Q000737:chemistry
chemical_list: D029968:Escherichia coli Proteins; C444040:F pilin, E coli; D008565:Membrane Proteins; D036781:Fimbriae Proteins; C076367:TrbI protein, E coli; D012697:Serine Endopeptidases; C026515:type I signal peptidase