Intermediaries of biological electron transport

Although the transport of electrons within a single protein or complex has been studied in detail using structural and functional techniques, the transfer of electrons between proteins remains somewhat mysterious. This is due to the presence of the aqueous solvent, as well as the dynamic and transient nature of the molecular interaction between proteins and the electron transfer event itself.A new study led by the Institute for Bioengineering of Catalonia (IBEC) addresses this challenge using nanometric and single-protein techniques to allow observation of a fundamental process that, until now, had been very difficult to investigate using macroscopic techniques.The researchers discovered that long-distance charge transport between two key proteins in the mitochondrial respiratory chain — cytochrome c and respiratory complex III — is mediated by protons and superoxide ions, which are reactive oxygen species.This work culminates a line of research developed for almost 10 years. It was demonstrated in 2018 that two proteins can transfer electrons over long distances through the aqueous solution (Gouy-Chapman conduit) without forming a stable complex. Subsequently, in 2022, a second study revealed how phosphorylation regulates this process and its relevance in cell signalling. Now the charge carriers have been identified and a model has been proposed to explain this process.Understanding these mechanisms is crucial, given that mitochondria are the powerhouses of all cells and alterations to them are associated with numerous diseases.