Department of Molecular Biology, Princeton University, Princeton, NJ 08544.
Department of Molecular Biology, Princeton University, Princeton, NJ 08544
Proc Natl Acad Sci U S A. 2022 Jan 4;119(1). doi: 10.1073/pnas.2114997119.
The biogenesis of integral β-barrel outer membrane proteins (OMPs) in gram-negative bacteria requires transport by molecular chaperones across the aqueous periplasmic space. Owing in part to the extensive functional redundancy within the periplasmic chaperone network, specific roles for molecular chaperones in OMP quality control and assembly have remained largely elusive. Here, by deliberately perturbing the OMP assembly process through use of multiple folding-defective substrates, we have identified a role for the periplasmic chaperone Skp in ensuring efficient folding of OMPs by the β-barrel assembly machine (Bam) complex. We find that β-barrel substrates that fail to integrate into the membrane in a timely manner are removed from the Bam complex by Skp, thereby allowing for clearance of stalled Bam-OMP complexes. Following the displacement of OMPs from the assembly machinery, Skp subsequently serves as a sacrificial adaptor protein to directly facilitate the degradation of defective OMP substrates by the periplasmic protease DegP. We conclude that Skp acts to ensure efficient β-barrel folding by directly mediating the displacement and degradation of assembly-compromised OMP substrates from the Bam complex.
革兰氏阴性细菌中完整β-桶状跨膜蛋白（OMP）的生物发生需要分子伴侣穿过水相周质空间进行运输。部分由于周质伴侣网络具有广泛的功能冗余，分子伴侣在 OMP 质量控制和组装中的具体作用在很大程度上仍然难以捉摸。在这里，我们通过使用多种折叠缺陷底物故意扰乱 OMP 组装过程，鉴定了周质伴侣 Skp 在确保 Bam 复合物有效折叠 OMP 中的作用。我们发现，不能及时整合到膜中的β-桶状底物会被 Skp 从 Bam 复合物中去除，从而允许停滞的 Bam-OMP 复合物清除。在从组装机制中置换 OMP 后，Skp 随后充当牺牲适应蛋白，直接促进周质蛋白酶 DegP 降解有缺陷的 OMP 底物。我们得出结论，Skp 通过直接介导组装受损的 OMP 底物从 Bam 复合物中的置换和降解，来确保有效的β-桶状折叠。
