Author:
Ishigami Izumi,Zatsepin Nadia A.,Hikita Masahide,Conrad Chelsie E.,Nelson Garrett,Coe Jesse D.,Basu Shibom,Grant Thomas D.,Seaberg Matthew H.,Sierra Raymond G.,Hunter Mark S.,Fromme Petra,Fromme Raimund,Yeh Syun-Ru,Rousseau Denis L.
Abstract
Cytochromecoxidase (CcO), the terminal enzyme in the electron transfer chain, translocates protons across the inner mitochondrial membrane by harnessing the free energy generated by the reduction of oxygen to water. Several redox-coupled proton translocation mechanisms have been proposed, but they lack confirmation, in part from the absence of reliable structural information due to radiation damage artifacts caused by the intense synchrotron radiation. Here we report the room temperature, neutral pH (6.8), damage-free structure of bovine CcO (bCcO) in the carbon monoxide (CO)-bound state at a resolution of 2.3 Å, obtained by serial femtosecond X-ray crystallography (SFX) with an X-ray free electron laser. As a comparison, an equivalent structure was obtained at a resolution of 1.95 Å, from data collected at a synchrotron light source. In the SFX structure, the CO is coordinated to the hemea3iron atom, with a bent Fe–C–O angle of ∼142°. In contrast, in the synchrotron structure, the Fe–CO bond is cleaved; CO relocates to a new site near CuB, which, in turn, moves closer to the hemea3iron by ∼0.38 Å. Structural comparison reveals that ligand binding to the hemea3iron in the SFX structure is associated with an allosteric structural transition, involving partial unwinding of the helix-X between hemeaanda3, thereby establishing a communication linkage between the two heme groups, setting the stage for proton translocation during the ensuing redox chemistry.
Funder
HHS | NIH | National Institute of General Medical Sciences
National Science Foundation
Publisher
Proceedings of the National Academy of Sciences
Cited by
55 articles.
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