Structure of plant photosystem I-plastocyanin complex reveals strong hydrophobic interactions
Ido Caspy, Maria Fadeeva, Sebastian Kuhlgert, Anna Borovikova-Sheinker, Daniel Klaiman, Gal Masrati, Friedel Drepper, Nir Ben‐Tal, Michael Hippler, Nathan Nelson
Abstract
Photosystem I is defined as plastocyanin-ferredoxin oxidoreductase. Taking advantage of genetic engineering, kinetic analyses and cryo-EM, our data provide novel mechanistic insights into binding and electron transfer between PSI and Pc. Structural data at 2.74 Å resolution reveals strong hydrophobic interactions in the plant PSI-Pc ternary complex, leading to exclusion of water molecules from PsaA-PsaB/Pc interface once the PSI-Pc complex forms. Upon oxidation of Pc, a slight tilt of bound oxidized Pc allows water molecules to accommodate the space between Pc and PSI to drive Pc dissociation. Such a scenario is consistent with the six times larger dissociation constant of oxidized as compared with reduced Pc and mechanistically explains how this molecular machine optimized electron transfer for fast turnover.