In the electron transfer (ET) reaction from cytochrome c (Cyt c) to cytochrome c oxidase (CcO), we determined the number and sites of the hydration water released from the protein surface upon the formation of the ET complex by evaluating the osmotic pressure dependence of kinetics for the ET from Cyt c to CcO. We identified that ∼20 water molecules were dehydrated in complex formation under turnover conditions, and systematic Cyt c mutations in the interaction site for CcO revealed that nearly half of the released hydration water during the complexation were located around Ile81, one of the hydrophobic amino acid residues near the exposed heme periphery of Cyt c. Such a dehydration dominantly compensates for the entropy decrease due to the association of Cyt c with CcO, resulting in the entropy-driven ET reaction. The energetic analysis of the interprotein interactions in the ET complex predicted by the docking simulation suggested the formation of hydrophobic interaction sites surrounding the exposed heme periphery of Cyt c in the Cyt c–CcO interface (a ‘molecular breakwater'). Such sites would contribute to the formation of the hydrophobic ET pathway from Cyt c to CcO by blocking water access from the bulk water phase.
-
Cover Image
Cover Image
Glutamine transport across cell membranes is performed by a variety of transporters, including the alanine serine cysteine transporter 2 (ASCT2). The substrate-binding site of ASCT2 was proposed to be specific for small amino acids with neutral side chains, excluding basic substrates such as lysine. In this issue Ndaru and co-workers (pp. 1443–1457) expand the substrate specificity of ASCT2 to include amino acid substrates with positively charged side chains. The image shows the docking pose of L-DAB and L-DAP, from the side view of the ASCT2 homology model in the outward-open conformation.The image was provided by Christof Grewer.
Osmotic pressure effects identify dehydration upon cytochrome c–cytochrome c oxidase complex formation contributing to a specific electron pathway formation
Wataru Sato, Seiji Hitaoka, Takeshi Uchida, Kyoko Shinzawa-Itoh, Kazunari Yoshizawa, Shinya Yoshikawa, Koichiro Ishimori; Osmotic pressure effects identify dehydration upon cytochrome c–cytochrome c oxidase complex formation contributing to a specific electron pathway formation. Biochem J 30 April 2020; 477 (8): 1565–1578. doi: https://doi.org/10.1042/BCJ20200023
Download citation file:
Sign in
Sign in to your personal account
Captcha Validation Error. Please try again.