Evidence of a Bacterial Receptor for Lysozyme: Binding of Lysozyme to the Anti-s Factor RsiV Controls Activation of the ECF s Factor s

s factors endow RNA polymerase with promoter specificity in bacteria. Extra-Cytoplasmic Function (ECF) s factors represent the largest and most diverse family of s factors. Most ECF s factors must be activated in response to an external signal. One mechanism of activation is the stepwise proteolytic destruction of an anti-s 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-s factor rather than the site-1 protease is the sensor. We provide evidence suggesting that the anti-s 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 s 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-s factor RsiV directly binds to lysozyme and muramidase activity is not required for s 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 s. This suggests a novel mechanism in which conformational change in a substrate controls the cleavage susceptibility for signal peptidase. Thus, unlike other ECF s factors which require regulated intramembrane proteolysis for activation, the sensor for s activation is not the site-1 protease but the anti-s factor. Citation: Hastie JL, Williams KB, Sepúlveda C, Houtman JC, Forest KT, et al. (2014) Evidence of a Bacterial Receptor for Lysozyme: Binding of Lysozyme to the Antis Factor RsiV Controls Activation of the ECF s Factor s. PLoS Genet 10(10): e1004643. doi:10.1371/journal.pgen.1004643 Editor: Carol A. Gross, University of California, San Francisco, United States of America Received August 1, 2013; Accepted July 31, 2014; Published October 2, 2014 Copyright: 2014 Hastie et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by Public Health Service grant R01AI087834 from the National Institutes for Allergy and Infectious Disease of the National Institutes of Health (www.nih.gov) to CDE, and an NIH training grant T32 AI07511 to KBW. JLH was supported by the American Heart Association (http://www. heart.org/) 13PRE14650053. CS was supported by a Becas Chile fellowship (http://www.conicyt.cl/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * Email: [email protected] . These authors contributed equally to this work.