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Activation of the extracytoplasmic function σ factor σV by lysozyme
Journal article   Open access   Peer reviewed

Activation of the extracytoplasmic function σ factor σV by lysozyme

Theresa D Ho and Craig D Ellermeier
Molecular microbiology, Vol.112(2), pp.410-419
08/2019
DOI: 10.1111/mmi.14348
PMCID: PMC6703919
PMID: 31286585
url
https://doi.org/10.1111/mmi.14348View
Published (Version of record) Open Access

Abstract

Summary σV is an extracytoplasmic function (ECF) σ factor that is found exclusively in Firmicutes including Bacillus subtilis and the opportunistic pathogens Clostridioides difficile and Enterococcus faecalis. σV is activated by lysozyme and is required for lysozyme resistance. The activity of σV is normally inhibited by the anti‐σ factor RsiV, a transmembrane protein. RsiV acts as a receptor for lysozyme. The binding of lysozyme to RsiV triggers a signal transduction cascade which results in degradation of RsiV and activation of σV. Like the anti‐σ factors for several other ECF σ factors, RsiV is degraded by a multistep proteolytic cascade that is regulated at the step of site‐1 cleavage. Unlike other anti‐σ factors, site‐1 cleavage of RsiV is not dependent upon a site‐1 protease whose activity is regulated. Instead constitutively active signal peptidase cleaves RsiV at site‐1 in a lysozyme‐dependent manner. The activation of σV leads to the transcription of genes, which encode proteins required for lysozyme resistance. In the absence of lysozyme, RsiV (red) and inhibits σV activity (green). Lysozyme (blue) binds RsiV inducing σV activation. RsiV binds to lysozyme exposing the membrane‐embedded site‐1 cleavage site of RsiV to cleavage by signal peptidase. This leads to cleavage of RsiV by the site‐2 protease and further degradation of the cytosolic portion of RsiV. Thus, freeing σV to interact with RNA polymerase and σV promoters to induce lysozyme resistance.

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