Heme Ruffling in Cytochrome c As a Mechanism to Control Electron Transfer
In order to probe the effect of heme “ruffling” on electron transport, we studied three cytochromes that display a wide variation in the protein-induced distortion along this mode1. As the ruffling distortion is increased, the ruffling mode frequency decreases from ~ 60 cm-1 to ~ 45 cm-1. The photoreduction cross-section is also measured and found to decrease exponentially as a function of the magnitude of the distortion. Given the similarity in the distance between the heme and the nearest aromatic amino acid for all three proteins, the order-of-magnitude changes in photoreduction rate demonstrate that the ruffling coordinate can serve as a control mechanism for electron transport in heme proteins. For example, major differences in heme ruffling are noted for cytochrome c when bound to the mitochondrial membrane compared to its solution structure.
1. Y. Sun, A. Benabbas, W. Zeng, J. Kleingardner, K. Bren, and P. M. Champion, Proc. Natl. Acad. Sci.(USA) 111, 6570-6575 (2014).