title: PG0026 is the C-terminal signal peptidase of a novel secretion system of Porphyromonas gingivalis.
abstract: Protein substrates of a novel secretion system of Porphyromonas gingivalis contain a conserved C-terminal domain (CTD) of ∼70-80 amino acid residues that is essential for their secretion and attachment to the cell surface. The CTD itself has not been detected in mature substrates, suggesting that it may be removed by a novel signal peptidase. More than 10 proteins have been shown to be essential for the proper functioning of the secretion system, and one of these, PG0026, is a predicted cysteine proteinase that also contains a CTD, suggesting that it may be a secreted component of the secretion system and a candidate for being the CTD signal peptidase. A PG0026 deletion mutant was constructed along with a PG0026C690A targeted mutant encoding an altered catalytic Cys residue. Analysis of clarified culture fluid fractions by SDS-PAGE and mass spectrometry revealed that the CTD was released intact into the surrounding medium in the wild type strain, but not in the PG0026 mutant strains. Western blot experiments revealed that the maturation of a model substrate was stalled at the CTD-removal step specifically in the PG0026 mutants, and whole cell ELISA experiments demonstrated partial secretion of substrates to the cell surface. The CTD was also shown to be accessible at the cell surface in the PG0026 mutants, suggesting that the CTD was secreted but could not be cleaved. The data indicate that PG0026 is responsible for the cleavage of the CTD signal after substrates are secreted across the OM.
authors.affiliation: Oral Health Cooperative Research Centre, Melbourne Dental School, and Bio21 Institute, The University of Melbourne, Melbourne, Victoria 3010, Australia.
authors.forename: Michelle D
authors.initials: MD
authors.lastname: Glew
authors.forename: Paul D
authors.initials: PD
authors.lastname: Veith
authors.forename: Benjamin
authors.initials: B
authors.lastname: Peng
authors.forename: Yu-Yen
authors.initials: YY
authors.lastname: Chen
authors.forename: Dhana G
authors.initials: DG
authors.lastname: Gorasia
authors.forename: Qiaohui
authors.initials: Q
authors.lastname: Yang
authors.forename: Nada
authors.initials: N
authors.lastname: Slakeski
authors.forename: Dina
authors.initials: D
authors.lastname: Chen
authors.forename: Caroline
authors.initials: C
authors.lastname: Moore
authors.forename: Simon
authors.initials: S
authors.lastname: Crawford
authors.forename: Eric C
authors.initials: EC
authors.lastname: Reynolds
mesh_terms: D000595:Amino Acid Sequence; D015153:Blotting, Western; D019295:Computational Biology; D020285:Cryoelectron Microscopy; D004591:Electrophoresis, Polyacrylamide Gel; D004797:Enzyme-Linked Immunosorbent Assay; D013058:Mass Spectrometry; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008855:Microscopy, Electron, Scanning; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D016966:Porphyromonas gingivalis / Q000201:enzymology* / Q000378:metabolism*; D017384:Sequence Deletion / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D012697:Serine Endopeptidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D037521:Virulence Factors / Q000235:genetics
chemical_list: D008565:Membrane Proteins; D037521:Virulence Factors; D012697:Serine Endopeptidases; C026515:type I signal peptidase