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Use of cell wall stress to characterize σ 22 (AlgT/U) activation by regulated proteolysis and its regulon in Pseudomonas aeruginosa
Author(s) -
Wood Lynn F.,
Ohman Dennis E.
Publication year - 2009
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2009.06635.x
Subject(s) - regulon , sigma factor , operon , biology , periplasmic space , mutant , proteolysis , microbiology and biotechnology , gene , biochemistry , promoter , gene expression , escherichia coli , enzyme
Summary MucA sequesters extracytoplasmic function (ECF) σ 22 ( algT/U encoded) from target promoters including P algD for alginate biosynthesis. We have shown that cell wall stress (e.g. d ‐cycloserine) is a potent inducer of the algD operon. Here we showed that MucB, encoded by the algT‐mucABCD operon, interacts with MucA in the sigma–sequestration complex. We hypothesized that AlgW protease (a DegS homologue) is activated by cell wall stress to cleave MucA and release σ 22 . When strain PAO1 was exposed to d ‐cycloserine, MucA was degraded within just 10 min, and σ 22 was activated. However, in an algW mutant, MucA was stable with no increased σ 22 activity. Studies on a yaeL mutant, defective in an RseP/YaeL homologue, suggest that YaeL protease cleaves MucA only after cleavage by AlgW. A defect in mucD , encoding a periplasmic HtrA/DegP homologue, caused MucA instability, suggesting MucD degrades cell wall stress signals. Overall, these data indicate that cell wall stress signals release σ 22 by regulated intramembrane proteolysis (RIP). Microarray analyses identified genes of the early and late cell wall stress stimulon, which included genes for alginate production. The subset of genes in the σ 22 regulon was then determined, which included gene products predicted to contribute to recovery from cell wall stress.