Search

Skeletal muscle is more resilient to ischemia-reperfusion injury than other organs. Tissue specific post-translational modifications of cytochrome c (Cytc) are involved in ischemia-reperfusion injury by regulating mitochondrial respiration and apoptosis. Here, we describe an acetylation site of Cytc, lysine 39 (K39), which was mapped in ischemic porcine skeletal muscle and removed by sirtuin5 in vitro. Using purified protein and cellular double knockout models, we show that K39 acetylation and acetylmimetic K39Q replacement increases cytochrome c oxidase (COX) activity and ROS scavenging while inhibiting apoptosis via decreased binding to Apaf-1, caspase cleavage and activity, and cardiolipin peroxidase activity. These results are discussed with X-ray crystallography structures of K39 acetylated (1.50 Å) and acetylmimetic K39Q Cytc (1.36 Å) and NMR dynamics. We propose that K39 acetylation is an adaptive response that controls electron transport chain flux, allowing skeletal muscle to meet heightened energy demand while simultaneously providing the tissue with robust resilience to ischemia-reperfusion injury. The authors report that acetylation of cytochrome c on K39 acts as a molecular switch in ischemic skeletal muscle, but not other tissues, to increase respiration and prevent apoptosis. This gives skeletal muscle robust resilience to ischemia and ischemia-reperfusion injury. [ABSTRACT FROM AUTHOR]

It has been recently shown that electron transfer between mitochondrial cytochrome c and the cytochrome c1 subunit of the cytochrome bc1 can proceed at long-distance through the aqueous solution. Cytochrome c is thought to adjust its activity by changing the affinity for its partners via Tyr48 phosphorylation, but it is unknown how it impacts the nanoscopic environment, interaction forces, and long-range electron transfer. Here, we constrain the orientation and separation between cytochrome c1 and cytochrome c or the phosphomimetic Y48pCMF cytochrome c, and deploy an array of single-molecule, bulk, and computational methods to investigate the molecular mechanism of electron transfer regulation by cytochrome c phosphorylation. We demonstrate that phosphorylation impairs long-range electron transfer, shortens the long-distance charge conduit between the partners, strengthens their interaction, and departs it from equilibrium. These results unveil a nanoscopic view of the interaction between redox protein partners in electron transport chains and its mechanisms of regulation. Electron transfer between mitochondrial cytochrome c and subunit of cytochrome bc1 can proceed at long distance. Here the authors investigate further the mechanism and show phosphorylation regulation of the interactions between the protein partners in the electron transport chain. [ABSTRACT FROM AUTHOR]

Post‐translational modifications frequently modulate protein functions. Lysine acetylation in particular plays a key role in interactions between respiratory cytochrome c and its metabolic partners. To date, in vivo acetylation of lysines at positions 8 and 53 has specifically been identified in mammalian cytochrome c, but little is known about the structural basis of acetylation‐induced functional changes. Here, we independently replaced these two residues in recombinant human cytochrome c with glutamine to mimic lysine acetylation and then characterized the structure and function of the resulting K8Q and K53Q mutants. We found that the physicochemical features were mostly unchanged in the two acetyl‐mimetic mutants, but their thermal stability was significantly altered. NMR chemical shift perturbations of the backbone amide resonances revealed local structural changes, and the thermodynamics and kinetics of electron transfer in mutants immobilized on gold electrodes showed an increase in both protein dynamics and solvent involvement in the redox process. We also observed that the K8Q (but not the K53Q) mutation slightly increased the binding affinity of cytochrome c to its physiological electron donor, cytochrome c1—which is a component of mitochondrial complex III, or cytochrome bc1—thus suggesting that Lys8 (but not Lys53) is located in the interaction area. Finally, the K8Q and K53Q mutants exhibited reduced efficiency as electron donors to complex IV, or cytochrome c oxidase. [ABSTRACT FROM AUTHOR]

• Respiratory chain organization is highly dynamic and adapts to cellular needs. • Supercomplex formation facilitates cytochrome c 2D sliding from complex III to IV. • Physical contact contributes to redox potential gap and electron transfer. • Long-distance electron transfer allows a faster turnover of cytochrome c. The supramolecular arrangement of respiratory complexes into supercomplexes is widely accepted. The common feature observed in the supercomplex architecture from organisms of diverse phylogenetic origin is the reduction of the distance between cytochrome bc 1 (complex III) and cytochrome c oxidase (complex IV). Such an arrangement reduces the dimensionality (from 3D to 2D) of the diffusional search of cytochrome c as the electron carrier that connects both complexes. In this scenario, our recent finding of additional binding sites for cytochrome c reinforces the concept of a "restrained 2D sliding pathway" onto the supercomplex surface. Herein, we analyze novel mechanistic insights into electron transfer towards cytochrome c , including modulation of the redox potential by physical contact as well as gated, long-range electron transfer through an aqueous solution. These data establish a new horizon for the understanding of electron transfer mechanisms beyond unique and well-orientated protein complexes. Multiple and dynamic long-distance conformational ensembles compatible with electron transfer could indeed contribute to the rapid adjustment of electron flow in response to changing cellular conditions. [ABSTRACT FROM AUTHOR]