A scaffold for quinone channeling between membrane and soluble bacterial oxidoreductases

Redox processes are at the heart of energetic metabolism that drives life on earth. By extension, complex and efficient electron transfer wires are necessary to connect the various metabolic pathways that are often located in distinct cellular compartments. Here, we uncovered a structural module that enables channeling of quinones from the membrane to various water-soluble redox catalytic units in prokaryotes. Using X-ray crystallography and cryo-electron microscopy, we determined the structure of the unusual bacterial formate dehydrogenase ForCE that contains four ForC catalytic subunits docked around a membrane-associated tetrameric ForE central scaffold. In the latter, a conserved domain that we propose to name helical membrane plugin (HMP) was identified as essential to link formate oxidation, in Bacillus subtilis, to the aerobic respiratory chain. Our bioinformatic analysis indicates that this HMP is associated with different quinone-reducing oxidoreductases, highlighting its broad importance as a functional unit to wire electrons between a given catalytic redox center and the quinone pool.