Inaba Kenji, Suzuki Mamoru, Maegawa Ken-ichi, Akiyama Shuji, Ito Koreaki, Akiyama Yoshinori
Medical Institute of Bioregulation, Kyushu University, Fukuoka 812-8582, Japan.
J Biol Chem. 2008 Dec 12;283(50):35042-52. doi: 10.1074/jbc.M806603200. Epub 2008 Oct 22.
The sigma(E) pathway of extracytoplasmic stress responses in Escherichia coli is activated through sequential cleavages of the anti-sigma(E) protein, RseA, by membrane proteases DegS and RseP. Without the first cleavage by DegS, RseP is unable to cleave full-length RseA. We previously showed that a PDZ-like domain in the RseP periplasmic region is essential for this negative regulation of RseP. We now isolated additional deregulated RseP mutants. Many of the mutations affected a periplasmic region that is N-terminal to the previously defined PDZ domain. We expressed these regions and determined their crystal structures. Consistent with a recent prediction, our results indicate that RseP has tandem, circularly permutated PDZ domains (PDZ-N and PDZ-C). Strikingly, almost all the strong mutations have been mapped around the ligand binding cleft region in PDZ-N. These results together with those of an in vitro reaction reproducing the two-step RseA cleavage suggest that the proteolytic function of RseP is controlled by ligand binding to PDZ-N.
大肠杆菌胞质外应激反应的σ(E)途径是通过膜蛋白酶DegS和RseP对抗σ(E)蛋白RseA的顺序切割而被激活的。如果没有DegS的首次切割，RseP就无法切割全长RseA。我们之前表明，RseP周质区域中的一个类PDZ结构域对于RseP的这种负调控至关重要。我们现在分离出了其他失调的RseP突变体。许多突变影响了一个位于先前定义的PDZ结构域N端的周质区域。我们表达了这些区域并确定了它们的晶体结构。与最近的预测一致，我们的结果表明RseP具有串联的、环状排列的PDZ结构域（PDZ-N和PDZ-C）。引人注目的是，几乎所有的强突变都定位在PDZ-N的配体结合裂隙区域周围。这些结果以及重现RseA两步切割的体外反应结果表明，RseP的蛋白水解功能受配体与PDZ-N结合的控制。
