Ma Chengying, Wang Chengkun, Luo Dingyi, Yan Lu, Yang Wenxian, Li Ningning, Gao Ning
State Key Laboratory of Membrane Biology, Peking-Tsinghua Joint Centre for Life Sciences, School of Life Sciences, Peking University, Beijing, China.
National Biomedical Imaging Center, Peking University, Beijing, China.
Cell Res. 2022 Feb;32(2):176-189. doi: 10.1038/s41422-021-00598-3. Epub 2022 Jan 3.
The lateral segregation of membrane constituents into functional microdomains, conceptually known as lipid raft, is a universal organization principle for cellular membranes in both prokaryotes and eukaryotes. The widespread Stomatin, Prohibitin, Flotillin, and HflK/C (SPFH) family proteins are enriched in functional membrane microdomains at various subcellular locations, and therefore were hypothesized to play a scaffolding role in microdomain formation. In addition, many SPFH proteins are also implicated in highly specific processes occurring on the membrane. However, none of these functions is understood at the molecular level. Here we report the structure of a supramolecular complex that is isolated from bacterial membrane microdomains and contains two SPFH proteins (HflK and HflC) and a membrane-anchored AAA+ protease FtsH. HflK and HflC form a circular 24-mer assembly, featuring a laterally segregated membrane microdomain (20 nm in diameter) bordered by transmembrane domains of HflK/C and a completely sealed periplasmic vault. Four FtsH hexamers are embedded inside this microdomain through interactions with the inner surface of the vault. These observations provide a mechanistic explanation for the role of HflK/C and their mitochondrial homologs prohibitins in regulating membrane-bound AAA+ proteases, and suggest a general model for the organization and functionalization of membrane microdomains by SPFH proteins.
膜成分侧向分离形成功能性微结构域，在概念上被称为脂筏，这是原核生物和真核生物细胞膜普遍的组织原则。广泛存在的司他汀、抑制素、浮舰蛋白和HflK/C（SPFH）家族蛋白在不同亚细胞位置的功能性膜微结构域中富集，因此被推测在微结构域形成中起支架作用。此外，许多SPFH蛋白还参与膜上发生的高度特异性过程。然而，这些功能在分子水平上均未得到理解。在此，我们报道了一种超分子复合物的结构，该复合物从细菌膜微结构域中分离得到，包含两种SPFH蛋白（HflK和HflC）以及一种膜锚定的AAA+蛋白酶FtsH。HflK和HflC形成一个环状的24聚体组装体，其特征是有一个由HflK/C的跨膜结构域界定的侧向分离的膜微结构域（直径20纳米）和一个完全封闭的周质穹顶。四个FtsH六聚体通过与穹顶内表面的相互作用嵌入这个微结构域内部。这些观察结果为HflK/C及其线粒体同源物抑制素在调节膜结合的AAA+蛋白酶中的作用提供了一个机制解释，并提出了一个由SPFH蛋白介导的膜微结构域组织和功能化的通用模型。
