Structure of the Cytochrome b_6f Complex of Oxygenic Photosynthesis: Tuning the Cavity

摘要

The cytochrome b_6f complex provides the electronic connection between the photosystem I and photosystem II reaction centers of oxygenic photosynthesis and generates a transmembrane electrochemical proton gradient for adenosine triphosphate synthesis. A 3.0 angstrom crystal structure of the dimeric b_6f complex from the thermophilic cyanobacterium Mastigocladus laminosus reveals a large quinone exchange cavity, stabilized by lipid, in which plastoqui-none, a quinone-analog inhibitor, and a novel heme are bound. The core of the b_6f complex is similar to the analogous respiratory cytochrome bc_1 complex, but the domain arrangement outside the core and the complement of prosthetic groups are strikingly different. The motion of the Rieske iron-sulfur protein extrinsic domain, essential for electron transfer, must also be different in the b_6f complex.