title: Overexpression of CupB5 activates alginate overproduction in Pseudomonas aeruginosa by a novel AlgW-dependent mechanism.
abstract: In Pseudomonas aeruginosa, alginate overproduction, also known as mucoidy, is negatively regulated by the transmembrane protein MucA, which sequesters the alternative sigma factor AlgU. MucA is degraded via a proteolysis pathway that frees AlgU from sequestration, activating alginate biosynthesis. Initiation of this pathway normally requires two signals: peptide sequences in unassembled outer-membrane proteins (OMPs) activate the AlgW protease, and unassembled lipopolysaccharides bind periplasmic MucB, releasing MucA and facilitating its proteolysis by activated AlgW. To search for novel alginate regulators, we screened a transposon library in the non-mucoid reference strain PAO1, and identified a mutant that confers mucoidy through overexpression of a protein encoded by the chaperone-usher pathway gene cupB5. CupB5-dependent mucoidy occurs through the AlgU pathway and can be reversed by overexpression of MucA or MucB. In the presence of activating OMP peptides, peptides corresponding to a region of CupB5 needed for mucoidy further stimulated AlgW cleavage of MucA in vitro. Moreover, the CupB5 peptide allowed OMP-activated AlgW cleavage of MucA in the presence of the MucB inhibitor. These results support a novel mechanism for conversion to mucoidy in which the proteolytic activity of AlgW and its ability to compete with MucB for MucA is mediated by independent peptide signals.
authors.affiliation: Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
authors.forename: Anna K
authors.initials: AK
authors.lastname: de Regt
authors.forename: Yeshi
authors.initials: Y
authors.lastname: Yin
authors.forename: T Ryan
authors.initials: TR
authors.lastname: Withers
authors.forename: Xin
authors.initials: X
authors.lastname: Wang
authors.forename: Tania A
authors.initials: TA
authors.lastname: Baker
authors.forename: Robert T
authors.initials: RT
authors.lastname: Sauer
authors.forename: Hongwei D
authors.initials: HD
authors.lastname: Yu
mesh_terms: D000464:Alginates; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D004251:DNA Transposable Elements; D015964:Gene Expression Regulation, Bacterial; D020723:Glucuronic Acid / Q000096:biosynthesis; D006603:Hexuronic Acids; D018832:Molecular Chaperones / Q000378:metabolism; D009154:Mutation; D021382:Protein Sorting Signals; D011550:Pseudomonas aeruginosa / Q000235:genetics* / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism; D012808:Sigma Factor / Q000378:metabolism
chemical_list: C079619:AlgU protein, Pseudomonas aeruginosa; C097646:AlgW protein, Pseudomonas aeruginosa; D000464:Alginates; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D006603:Hexuronic Acids; D018832:Molecular Chaperones; C107895:MucA protein, Pseudomonas; D021382:Protein Sorting Signals; D012097:Repressor Proteins; D012808:Sigma Factor; D020723:Glucuronic Acid