σE is an alternative sigma factor involved in a pathway of extracytoplasmic stress responses in Escherichia coli. Under normal growth conditions, σE activity is down-regulated by the membrane-bound anti-σE protein, RseA. Extracytoplasmic stress signals induce degradation of RseA by two successive proteolytic events: DegS-catalyzed first cleavage at a periplasmic site followed by YaeL-mediated second proteolysis at an intramembrane region. Normally, the second reaction (site-2 proteolysis) only occurs after the first cleavage (site-1 cleavage). Here, we show that YaeL variants with the periplasmic PDZ domain deleted or mutated allows unregulated cleavage of RseA and consequent σE activation. It was also found that a glutamine-rich region in the periplasmic domain of RseA was required for the avoidance of the YaeL-mediated proteolysis in the absence of site-1 cleavage. These results indicate that multiple negative elements both in the enzyme (PDZ domain) and in the substrate (glutamine-rich region) determine the strict dependence of the site-2 proteolysis on the site-1 cleavage.
展开▼
机译:σ E sup>是大肠杆菌中胞浆外应激反应途径中涉及的另一种sigma因子。在正常生长条件下,膜结合的抗σ E sup>蛋白RseA下调了σ E sup>的活性。胞外应激信号通过两个连续的蛋白水解事件诱导RseA降解:DegS催化的在周质位点的第一次切割,然后在膜内区域的YaeL介导的第二次蛋白水解。通常,第二个反应(位点2的蛋白水解)仅在第一次裂解(位点1的裂解)之后发生。在这里,我们显示缺失或突变了周质PDZ结构域的YaeL变体允许RseA的裂解不受调控,从而导致σ E sup>活化。还发现,在没有位点1裂解的情况下,RseA的周质结构域中富含谷氨酰胺的区域是避免YaeL介导的蛋白水解所必需的。这些结果表明,酶(PDZ域)和底物(富含谷氨酰胺的区域)中的多个负元素决定了site-2蛋白水解对site-1裂解的严格依赖性。
展开▼