[Lecture] Computational Studies of Electron Transfer in Multi-Heme Proteins
Speaker: Dr. Xiuyun Jiang, Department of Physic and Astronomy, University College London
Date: Jan, 13, 2020, 10:00 am
Location: Room B311, Zengchengkui Building, Siming Campus
Abstrac: Bacteria like Shewanella and Geobacter are species that express multi-heme proteins which enable them to respire and survive without oxygen by reduction of extracellular solid substrates. Multi-heme proteins are fascinating biomolecules that bind several redox-active heme cofactors in close distance. They have attracted much attention recently due to their prominent role in mediating extracellular electron transport. Based on Marcus theory and the electron hopping model (i.e., electron transport through the protein occurs via sequential electron hopping along the heme chains), I have used density functional theory (DFT) and molecular dynamics (MD) simulation to calculate all heme-to-heme electron transfer (ET) rate constants in three ubiquitous multi-heme proteins binding 4 and 10 heme cofactors. My calculations revealed that electron hopping through these proteins is strongly enhanced by cysteines that insert in the space between heme groups. We believe this to be a general design principle in multi-heme proteins for acceleration of ET steps that would otherwise be too slow for biological respiration. In the second part of my presentation, I will talk about a collaborated work to verify our computed rate constants. To this end, our experimental collaborators docked a Ru-chromophore close to a terminal heme of one of the multi-heme proteins studied and used ultrafast pump-probe spectroscopy to monitor electron injection in the protein and subsequent relaxation dynamics. From these measurements we could extract a heme-heme ET rate that is in good agreement with our predicted result.