Electron transfer in the respiratory chain at low salinity
Ana Paula Lobez, Fēi Wú, Justin M. Di Trani, John L. Rubinstein, Mikael Oliveberg, Peter Brzezinski, Agnes Moe
Abstract
Abstract Recent studies have established that cellular electrostatic interactions are more influential than assumed previously. Here, we use cryo-EM and perform steady-state kinetic studies to investigate electrostatic interactions between cytochrome (cyt.) c and the complex (C) III 2 -IV supercomplex from Saccharomyces cerevisiae at low salinity. The kinetic studies show a sharp transition with a Hill coefficient ≥2, which together with the cryo-EM data at 2.4 Å resolution indicate multiple cyt. c molecules bound along the supercomplex surface. Negatively charged loops of CIII 2 subunits Qcr6 and Qcr9 become structured to interact with cyt. c . In addition, the higher resolution allows us to identify water molecules in proton pathways of CIV and, to the best of our knowledge, previously unresolved cardiolipin molecules. In conclusion, the lowered electrostatic screening renders engagement of multiple cyt. c molecules that are directed by electrostatically structured CIII 2 loops to conduct electron transfer between CIII 2 and CIV.