title: Evidence of a bacterial receptor for lysozyme: binding of lysozyme to the anti-σ factor RsiV controls activation of the ecf σ factor σV.
abstract: σ factors endow RNA polymerase with promoter specificity in bacteria. Extra-Cytoplasmic Function (ECF) σ factors represent the largest and most diverse family of σ factors. Most ECF σ factors must be activated in response to an external signal. One mechanism of activation is the stepwise proteolytic destruction of an anti-σ factor via Regulated Intramembrane Proteolysis (RIP). In most cases, the site-1 protease required to initiate the RIP process directly senses the signal. Here we report a new mechanism in which the anti-σ factor rather than the site-1 protease is the sensor. We provide evidence suggesting that the anti-σ factor RsiV is the bacterial receptor for the innate immune defense enzyme, lysozyme. The site-1 cleavage site is similar to the recognition site of signal peptidase and cleavage at this site is required for σV activation in Bacillus subtilis. We reconstitute site-1 cleavage in vitro and demonstrate that it requires both signal peptidase and lysozyme. We demonstrate that the anti-σ factor RsiV directly binds to lysozyme and muramidase activity is not required for σV activation. We propose a model in which the binding of lysozyme to RsiV activates RsiV for signal peptidase cleavage at site-1, initiating proteolytic destruction of RsiV and activation of σV. This suggests a novel mechanism in which conformational change in a substrate controls the cleavage susceptibility for signal peptidase. Thus, unlike other ECF σ factors which require regulated intramembrane proteolysis for activation, the sensor for σV activation is not the site-1 protease but the anti-σ factor.
authors.affiliation: Department of Microbiology, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Hastie
authors.affiliation: Department of Microbiology, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Kyle B
authors.initials: KB
authors.lastname: Williams
authors.affiliation: Department of Bacteriology, University of Wisconsin Madison, Madison, Wisconsin, United States of America.
authors.forename: Carolina
authors.initials: C
authors.lastname: Sepúlveda
authors.affiliation: Department of Microbiology, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Jon C
authors.initials: JC
authors.lastname: Houtman
authors.affiliation: Department of Bacteriology, University of Wisconsin Madison, Madison, Wisconsin, United States of America.
authors.forename: Katrina T
authors.initials: KT
authors.lastname: Forest
authors.affiliation: Department of Microbiology, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Craig D
authors.initials: CD
authors.lastname: Ellermeier
mesh_terms: D001412:Bacillus subtilis / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002151:Calorimetry / Q000379:methods; D016360:Clostridioides difficile / Q000378:metabolism; D010450:Endopeptidases / Q000378:metabolism; D013293:Enterococcus faecalis / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D009113:Muramidase / Q000235:genetics / Q000378:metabolism*; D043484:Proprotein Convertases / Q000235:genetics / Q000378:metabolism; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D012808:Sigma Factor; C421864:hen egg lysozyme; D009113:Muramidase; D010450:Endopeptidases; D043484:Proprotein Convertases; D012697:Serine Endopeptidases; C115575:membrane-bound transcription factor peptidase, site 1; C026515:type I signal peptidase; C021816:mutanolysin