title: Protein substrates of a novel secretion system are numerous in the Bacteroidetes phylum and have in common a cleavable C-terminal secretion signal, extensive post-translational modification, and cell-surface attachment.
abstract: The secretion of certain proteins in Porphyromonas gingivalis is dependent on a C-terminal domain (CTD). After secretion, the CTD is cleaved prior to extensive modification of the mature protein, probably with lipopolysaccharide, therefore enabling attachment to the cell surface. In this study, bioinformatic analyses of the CTD demonstrated the presence of three conserved sequence motifs. These motifs were used to construct Hidden Markov Models (HMMs) that predicted 663 CTD-containing proteins in 21 fully sequenced species of the Bacteroidetes phylum, while no CTD-containing proteins were predicted in species outside this phylum. Further HMM searching of Cytophaga hutchinsonii led to a total of 171 predicted CTD proteins in that organism alone. Proteomic analyses of membrane fractions and culture fluid derived from P. gingivalis and four other species containing predicted CTDs (Parabacteroides distasonis, Prevotella intermedia, Tannerella forsythia, and C. hutchinsonii) demonstrated that membrane localization, extensive post-translational modification, and CTD-cleavage were conserved features of the secretion system. The CTD cleavage site of 10 different proteins from 3 different species was determined and found to be similar to the cleavage site previously determined in P. gingivalis, suggesting that homologues of the C-terminal signal peptidase (PG0026) are responsible for the cleavage in these species.
authors.affiliation: Oral Health CRC, Melbourne Dental School, Bio21 Institute, The University of Melbourne , 720 Swanston Street, Victoria 3010, Australia.
authors.forename: Paul D
authors.initials: PD
authors.lastname: Veith
authors.forename: Nor A
authors.initials: NA
authors.lastname: Nor Muhammad
authors.forename: Stuart G
authors.initials: SG
authors.lastname: Dashper
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Likić
authors.forename: Dhana G
authors.initials: DG
authors.lastname: Gorasia
authors.forename: Dina
authors.initials: D
authors.lastname: Chen
authors.forename: Samantha J
authors.initials: SJ
authors.lastname: Byrne
authors.forename: Deanne V
authors.initials: DV
authors.lastname: Catmull
authors.forename: Eric C
authors.initials: EC
authors.lastname: Reynolds
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D058947:Bacterial Secretion Systems; D041963:Bacteroidetes / Q000378:metabolism; D008390:Markov Chains; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D016966:Porphyromonas gingivalis / Q000378:metabolism*; D018713:Prevotella intermedia / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D021382:Protein Sorting Signals; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems; D008565:Membrane Proteins; D021382:Protein Sorting Signals