Institute of Biological Chemistry, Academia Sinica, Taipei, 11529, Taiwan.
Department of Molecular and Cell Biology, California Institute for Quantitative Biosciences, University of California, Berkeley, CA, 94720, USA.
Nat Commun. 2017 Nov 15;8(1):1516. doi: 10.1038/s41467-017-01697-9.
Peptidoglycan (PG) is a highly cross-linked, protective mesh-like sacculus that surrounds the bacterial cytoplasmic membrane. Expansion of PG is tightly coupled to growth of a bacterial cell and requires hydrolases to cleave the cross-links for insertion of nascent PG material. In Escherichia coli, a proteolytic system comprising the periplasmic PDZ-protease Prc and the lipoprotein adaptor NlpI contributes to PG enlargement by regulating cellular levels of MepS, a cross-link-specific hydrolase. Here, we demonstrate how NlpI binds Prc to facilitate the degradation of its substrate MepS by structural and mutational analyses. An NlpI homodimer binds two molecules of Prc and forms three-sided MepS-docking cradles using its tetratricopeptide repeats. Prc forms a monomeric bowl-shaped structure with a lid-like PDZ domain connected by a substrate-sensing hinge that recognizes the bound C terminus of the substrate. In summary, our study reveals mechanistic details of protein degradation by the PDZ-protease Prc bound to its cognate adaptor protein.
肽聚糖 (PG) 是一种高度交联的保护性网格状囊泡，环绕着细菌细胞质膜。PG 的扩张与细菌细胞的生长紧密耦合，需要水解酶来切割交联以插入新生的 PG 物质。在大肠杆菌中，由周质 PDZ 蛋白酶 Prc 和脂蛋白接头 NlpI 组成的蛋白水解系统通过调节交联特异性水解酶 MepS 的细胞水平来促进 PG 扩大。在这里，我们通过结构和突变分析证明了 NlpI 如何结合 Prc 来促进其底物 MepS 的降解。NlpI 同源二聚体结合两个 Prc 分子，并使用其四肽重复形成三面 MepS 对接支架。Prc 形成单体碗状结构，其 PDZ 结构域带有盖状结构，通过底物感应铰链连接，该铰链识别结合底物的 C 末端。总之，我们的研究揭示了 PDZ 蛋白酶 Prc 与其同源衔接蛋白结合时的蛋白降解的机制细节。
