Takeda Hironori, Busto Jon V, Lindau Caroline, Tsutsumi Akihisa, Tomii Kentaro, Imai Kenichiro, Yamamori Yu, Hirokawa Takatsugu, Motono Chie, Ganesan Iniyan, Wenz Lena-Sophie, Becker Thomas, Kikkawa Masahide, Pfanner Nikolaus, Wiedemann Nils, Endo Toshiya
Faculty of Life Sciences, Kyoto Sangyo University, Kyoto, Japan.
Nara Institute of Science and Technology, Ikoma, Japan.
Nat Struct Mol Biol. 2023 Feb;30(2):176-187. doi: 10.1038/s41594-022-00897-2. Epub 2023 Jan 5.
Mitochondrial β-barrel proteins are essential for the transport of metabolites, ions and proteins. The sorting and assembly machinery (SAM) mediates their folding and membrane insertion. We report the cryo-electron microscopy structure of the yeast SAM complex carrying an early eukaryotic β-barrel folding intermediate. The lateral gate of Sam50 is wide open and pairs with the last β-strand (β-signal) of the substrate-the 19-β-stranded Tom40 precursor-to form a hybrid barrel in the membrane plane. The Tom40 barrel grows and curves, guided by an extended bridge with Sam50. Tom40's first β-segment (β1) penetrates into the nascent barrel, interacting with its inner wall. The Tom40 amino-terminal segment then displaces β1 to promote its pairing with Tom40's last β-strand to complete barrel formation with the assistance of Sam37's dynamic α-protrusion. Our study thus reveals a multipoint guidance mechanism for mitochondrial β-barrel folding.
线粒体β-桶状蛋白对于代谢物、离子和蛋白质的运输至关重要。分选与组装机制（SAM）介导它们的折叠和膜插入。我们报告了携带早期真核生物β-桶状折叠中间体的酵母SAM复合物的冷冻电子显微镜结构。Sam50的侧向门大开，并与底物的最后一条β链（β信号）——19条β链的Tom40前体——配对，在膜平面上形成一个杂合桶状结构。Tom40桶状结构在与Sam50的延伸桥的引导下生长并弯曲。Tom40的第一个β片段（β1）穿透新生桶状结构，与其内壁相互作用。然后，Tom40的氨基末端片段取代β1，促进其与Tom40的最后一条β链配对，在Sam37动态α突出结构的协助下完成桶状结构的形成。因此，我们的研究揭示了线粒体β-桶状折叠的多点引导机制。
