title: Cyclic Di-GMP-Regulated Periplasmic Proteolysis of a Pseudomonas aeruginosa Type Vb Secretion System Substrate.
abstract: We previously identified a second-messenger-regulated signaling system in the environmental bacterium Pseudomonas fluorescens which controls biofilm formation in response to levels of environmental inorganic phosphate. This system contains the transmembrane cyclic di-GMP (c-di-GMP) receptor LapD and the periplasmic protease LapG. LapD regulates LapG and controls the ability of this protease to process a large cell surface adhesin protein, LapA. While LapDG orthologs can be identified in diverse bacteria, predictions of LapG substrates are sparse. Notably, the opportunistic pathogen Pseudomonas aeruginosa harbors LapDG orthologs, but neither the substrate of LapG nor any associated secretion machinery has been identified to date. Here, we identified P. aeruginosa CdrA, a protein known to mediate cell-cell aggregation and biofilm maturation, as a substrate of LapG. We also demonstrated LapDG to be a minimal system sufficient to control CdrA localization in response to changes in the intracellular concentration of c-di-GMP. Our work establishes this biofilm signaling node as a regulator of a type Vb secretion system substrate in a clinically important pathogen.
  
  
  OBJECTIVE
  Here, the biological relevance of a conserved yet orphan signaling system in the opportunistic pathogen Pseudomonas aeruginosa is revealed. In particular, we identified the adhesin CdrA, the cargo of a two-partner secretion system, as a substrate of a periplasmic protease whose activity is controlled by intracellular c-di-GMP levels and a corresponding transmembrane receptor via an inside-out signaling mechanism. The data indicate a posttranslational control mechanism of CdrA via c-di-GMP, in addition to its established transcriptional regulation via the same second messenger.
authors.affiliation: Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA.
authors.forename: Richard B
authors.initials: RB
authors.lastname: Cooley
authors.affiliation: Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
authors.forename: T Jarrod
authors.initials: TJ
authors.lastname: Smith
authors.affiliation: Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA.
authors.forename: Wilfred
authors.initials: W
authors.lastname: Leung
authors.affiliation: Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA.
authors.forename: Valerie
authors.initials: V
authors.lastname: Tierney
authors.affiliation: Department of Microbiology, Immunology and Pathology, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, Colorado, USA.
authors.forename: Bradley R
authors.initials: BR
authors.lastname: Borlee
authors.affiliation: Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
authors.forename: George A
authors.initials: GA
authors.lastname: O'Toole
authors.affiliation: Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA hs293@cornell.edu.
authors.forename: Holger
authors.initials: H
authors.lastname: Sondermann
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D018441:Biofilms / Q000254:growth & development; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019897:Periplasm / Q000502:physiology*; D010802:Phylogeny; D011487:Protein Conformation; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000069320:Type V Secretion Systems / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D000069320:Type V Secretion Systems; C062025:bis(3',5')-cyclic diguanylic acid; D006152:Cyclic GMP