Abstract：
Membrane proteins carrying redox cofactors are key subunits of respiratory chain complexes, yet the exact path of their folding and maturation remains poorly understood. Here, using cryo-EM and structure prediction via Alphafold2, we generated models of early assembly intermediates of cytochrome b (Cytb), a central subunit of complex III. The predicted structure of the first assembly intermediate suggests how the binding of Cytb to the assembly factor Cbp3-Cbp6 imposes an open configuration to facilitate the acquisition of its heme cofactors. Moreover, structure predictions of the second intermediate indicate how hemes get stabilized by binding of the assembly factor Cbp4, with a concomitant weakening of the contact between Cbp3-Cbp6 and Cytb, preparing for the release of the fully hemylated protein from the assembly factors.
摘要：
携带氧化还原辅因子的膜蛋白是呼吸链复合物的关键亚基，然而，它们折叠和成熟的确切路径仍然知之甚少。这里,使用冷冻EM和通过Alphafold2进行结构预测，我们生成了细胞色素b（Cytb）的早期组装中间体模型，复合体III的中央亚单位。第一组装中间体的预测结构表明Cytb与组装因子Cbp3-Cbp6的结合如何施加开放构型以促进其血红素辅因子的获得。此外，第二个中间体的结构预测表明血红素如何通过组装因子Cbp4的结合而稳定，伴随着Cbp3-Cbp6和Cytb之间的接触减弱，准备从组装因子中释放完全溶血的蛋白质。
