Department of Chemistry, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan.
J Biol Chem. 2010 Dec 31;285(53):41222-31. doi: 10.1074/jbc.M110.163238. Epub 2010 Oct 29.
β-barrel membrane proteins in the mitochondrial outer membrane use the TOM40 complex to enter mitochondria and then the TOB/SAM complex to be assembled into the outer membrane. Tom7, a subunit of the TOM40 complex, regulates association of Mdm10 with the TOB complex. Here, we analyzed the role of Tom7 in assembly of β-barrel proteins, including Tom40, a central channel subunit of the TOM40 complex, and porin. Depletion of Tom7 decreased transient accumulation of Tom40 at the level of the TOB complex and retarded assembly of porin in vitro. On the other hand, overexpression of Tom7 resulted in enhanced accumulation of in vitro imported Tom40 in the TOB complex, yet it did not affect the in vitro assembly of porin. Site-specific photocross-linking in vivo revealed that Tom7 directly interacts with Tom40 through its transmembrane segment and with Mdm10. These results collectively show that Tom7 recruits Mdm10, enhancing its association with the MMM1 complex, to regulate timing of the release of Tom40 from the TOB complex for subsequent assembly into the TOM40 complex.
β-桶膜蛋白在线粒体的外膜中使用 TOM40 复合物进入线粒体，然后使用 TOB/SAM 复合物被组装到外膜中。TOM40 复合物的一个亚基 Tom7 调节 Mdm10 与 TOB 复合物的结合。在这里，我们分析了 Tom7 在β-桶膜蛋白组装中的作用，包括 Tom40（TOM40 复合物的中心通道亚基）和孔蛋白。Tom7 的缺失减少了 Tom40 在 TOB 复合物水平上的瞬时积累，并延迟了孔蛋白的体外组装。另一方面，Tom7 的过表达导致体外导入的 Tom40 在 TOB 复合物中的积累增加，但不影响孔蛋白的体外组装。体内定点光交联显示 Tom7 通过其跨膜片段直接与 Tom40 相互作用，并与 Mdm10 相互作用。这些结果共同表明，Tom7 招募 Mdm10，增强其与 MMM1 复合物的结合，以调节 Tom40 从 TOB 复合物中释放的时机，以便随后组装到 TOM40 复合物中。
