Schleiff E, Silvius J R, Shore G C
Department of Biochemistry, McGill University, Montreal, Quebec, Canada H3G 1Y6.
J Cell Biol. 1999 May 31;145(5):973-8. doi: 10.1083/jcb.145.5.973.
Insertion of newly synthesized proteins into or across the mitochondrial outer membrane is initiated by import receptors at the surface of the organelle. Typically, this interaction directs the precursor protein into a preprotein translocation pore, comprised of Tom40. Here, we show that a prominent beta-barrel channel protein spanning the outer membrane, human voltage- dependent anion-selective channel (VDAC), bypasses the requirement for the Tom40 translocation pore during biogenesis. Insertion of VDAC into the outer membrane is unaffected by plugging the translocation pore with a partially translocated matrix preprotein, and mitochondria containing a temperature-sensitive mutant of Tom40 insert VDAC at the nonpermissive temperature. Synthetic liposomes harboring the cytosolic domain of the human import receptor Tom20 efficiently insert newly synthesized VDAC, resulting in transbilayer transport of ATP. Therefore, Tom20 transforms newly synthesized cytosolic VDAC into a transmembrane channel that is fully integrated into the lipid bilayer.
新合成的蛋白质插入线粒体外膜或穿过线粒体外膜是由细胞器表面的输入受体启动的。通常，这种相互作用将前体蛋白导向由Tom40组成的前蛋白转运孔。在这里，我们表明，一种跨越外膜的突出的β-桶通道蛋白，即人类电压依赖性阴离子选择性通道（VDAC），在生物合成过程中绕过了对Tom40转运孔的需求。用部分转运的基质前蛋白堵塞转运孔，并不影响VDAC插入外膜，并且含有温度敏感型Tom40突变体的线粒体在非允许温度下仍能插入VDAC。携带人类输入受体Tom20胞质结构域的合成脂质体能够有效地插入新合成的VDAC，从而实现ATP的跨双层运输。因此，Tom20将新合成的胞质VDAC转化为完全整合到脂质双层中的跨膜通道。
