Phosphorylation disrupts long-distance electron transport in cytochrome c

Abstract

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.

The Protein Matrix of Plastocyanin Supports Long-Distance Charge Transport with Photosystem I and the Copper Ion Regulates Its Spatial Span and Conductance

“…Longer charge exchange distances are described by thermally activated multistep mechanisms; however they are incompatible with the available data of temperature-independent ETp. , It has been suggested that electrostatic potential driving ET induces a partial delocalization of the bridge electronic states able to promote long-range electron transfer without thermal activation . For the pair hC c /pC c 1 , molecular dynamics calculations revealed a cation depletion region between the interacting partners that hinders charge screening, extending the electric field between redox partners across the electrolyte interface. , In other words, the cognate partners establish a Gouy–Chapman conduit between them. , The results presented here support this view, as long-distance charge transport (low β) observed for Pc apo interacting with PSI is absent when Pc apo faces a noncognate sequence like that of the pIQAcys peptide. This extended charge exchange range of Pc apo /PSI with respect to Pc holo /PSI is favored for positive bias, driving electrons from Pc to PSI, as it occurs in nature.…”

“…To answer them, it seems reasonable to involve the aqueous solution region confined between the proteins and to avoid explanations based on conventional quantum tunneling since reported charge exchange distances ,,, exceed the range accessible by one- and two-step electron tunneling. Longer charge exchange distances are described by thermally activated multistep mechanisms; however they are incompatible with the available data of temperature-independent ETp. , It has been suggested that electrostatic potential driving ET induces a partial delocalization of the bridge electronic states able to promote long-range electron transfer without thermal activation .…”

“…The spatial span of the protein charge exchange is assessed by recording the probe current during retraction (Figure d), yielding a double-exponential current decay , (Figure e). The current–distance decay rate (β, nm –1 ) obtained by fitting current–distance plots is a proxy indicator of the interprotein charge exchange distance. ,,− In previous works, we measured β for oriented PSI , complexes facing a Pt/Ir probe at different probe and sample potential pairs, concluding that the current is gated by the probe potential with a minimal β value (longest charge exchange distance) of 2 nm –1 . Although β for Pc has not been reported, the gating of β by the sample potential was observed for azurin, which is a Pc analogue.…”

“…In previous works, we have addressed interprotein ET using an electrochemical scanning tunneling microscope (ECSTM). We mimic the interprotein ET-like situation facing protein partners bound to electrodes and located at nanometer proximity. , In this configuration, for a redox cognate pair of the respiratory chain, we measured current at distances as long as 12 nm through the aqueous solution. , Furthermore, the spatial span of the interprotein current in cytochrome c is regulated by phosphorylation, which highlights the biological relevance of this observation. In the absence of a redox chain in the electrolyte solution, such observations require a different mechanism than ET in the bound complex, raising several questions: can the ETp mechanisms operating in the polypeptide structures support charge transport between proteins through the solution?…”

Apoptotic proteins with non-apoptotic activity: expression and function in cancer

“…Cyto c activities are tightly regulated by posttranslational modifications [ 149 ]. Specifically, phosphorylation can serve as the switch between the multiple activities of the protein [ 150 ].…”