Department of Chemistry, Dartmouth College , Hanover, New Hampshire 03755, United States.
J Phys Chem B. 2013 Oct 24;117(42):12878-86. doi: 10.1021/jp402104r. Epub 2013 Jun 25.
Interactions of cytochrome c (cyt c) with a unique mitochondrial glycerophospholipid cardiolipin (CL) are relevant for the protein's function in oxidative phosphorylation and apoptosis. Binding to CL-containing membranes promotes cyt c unfolding and dramatically enhances the protein's peroxidase activity, which is critical in early stages of apoptosis. We have employed a collection of seven dansyl variants of horse heart cyt c to probe the sequence of steps in this functional transformation. Kinetic measurements have unraveled four distinct processes during CL-induced cyt c unfolding: rapid protein binding to CL liposomes; rearrangements of protein substructures with small unfolding energies; partial insertion of the protein into the lipid bilayer; and extensive protein restructuring leading to "open" extended structures. While early rearrangements depend on a hierarchy of foldons in the native structure, the later process of large-scale unfolding is influenced by protein interactions with the membrane surface. The opening of the cyt c structure exposes the heme group, which enhances the protein's peroxidase activity and also frees the C-terminal helix to aid in the translocation of the protein through CL membranes.
细胞色素 c（cyt c）与独特的线粒体甘油磷脂心磷脂（CL）的相互作用与该蛋白在氧化磷酸化和细胞凋亡中的功能相关。与含 CL 的膜结合促进 cyt c 展开，并显著增强蛋白的过氧化物酶活性，这在细胞凋亡的早期阶段至关重要。我们使用了一组来自马心 cyt c 的七个丹磺酰基变体来探测这个功能转化过程中的步骤顺序。动力学测量揭示了 CL 诱导 cyt c 展开过程中的四个不同过程：快速的蛋白与 CL 脂质体结合；具有小展开能的蛋白亚结构的重排；蛋白部分插入脂质双层；以及导致“打开”扩展结构的广泛蛋白重排。虽然早期的重排取决于天然结构中的折叠子层次结构，但后来的大规模展开过程受到蛋白与膜表面相互作用的影响。cyt c 结构的打开暴露出血红素基团，这增强了蛋白的过氧化物酶活性，并使 C 末端螺旋释放，以帮助蛋白通过 CL 膜转运。
