1] Laboratory of Membrane Biology and Biophysics, The Rockefeller University, 1230 York Avenue, New York, New York 10065, USA [2] Howard Hughes Medical Institute, 1230 York Avenue, New York, New York 10065, USA.
Howard Hughes Medical Institute, 1230 York Avenue, New York, New York 10065, USA.
Nature. 2015 Jul 23;523(7561):425-30. doi: 10.1038/nature14623.
Bacteria secrete peptides and proteins to communicate, to poison competitors, and to manipulate host cells. Among the various protein-translocation machineries, the peptidase-containing ATP-binding cassette transporters (PCATs) are appealingly simple. Each PCAT contains two peptidase domains that cleave the secretion signal from the substrate, two transmembrane domains that form a translocation pathway, and two nucleotide-binding domains that hydrolyse ATP. In Gram-positive bacteria, PCATs function both as maturation proteases and exporters for quorum-sensing or antimicrobial polypeptides. In Gram-negative bacteria, PCATs interact with two other membrane proteins to form the type 1 secretion system. Here we present crystal structures of PCAT1 from Clostridium thermocellum in two different conformations. These structures, accompanied by biochemical data, show that the translocation pathway is a large α-helical barrel sufficient to accommodate small folded proteins. ATP binding alternates access to the transmembrane pathway and also regulates the protease activity, thereby coupling substrate processing to translocation.
细菌通过分泌肽和蛋白质进行交流，毒害竞争对手，并操纵宿主细胞。在各种蛋白质转运机制中，含有肽酶的 ATP 结合盒转运蛋白（PCAT）结构简单，令人心动。每个 PCAT 包含两个肽酶结构域，可从底物中切割分泌信号，两个跨膜结构域形成一个转运途径，两个核苷酸结合结构域可水解 ATP。在革兰氏阳性菌中，PCAT 既是成熟蛋白酶，也是群体感应或抗菌多肽的外排泵。在革兰氏阴性菌中，PCAT 与另外两个膜蛋白相互作用形成 I 型分泌系统。本文呈现了两种不同构象的热纤梭菌 PCAT1 的晶体结构。这些结构以及生化数据表明，转运途径是一个大的α-螺旋桶，足以容纳折叠的小分子蛋白。ATP 结合可交替进入跨膜途径，并调节蛋白酶活性，从而将底物加工与转运偶联。
