Cryo-EM structures of intermediates suggest an alternative catalytic reaction cycle for cytochrome c oxidase

F. Kolbe,S. Safarian,H. Michel,S. Welsch,H. Müller,Ż. Piórek

doi:10.1038/s41467-021-27174-y

Abstract

Cytochrome c oxidases are among the most important and fundamental enzymes of life. Integrated into membranes they use four electrons from cytochrome c molecules to reduce molecular oxygen (dioxygen) to water. Their catalytic cycle has been considered to start with the oxidized form. Subsequent electron transfers lead to the E-state, the R-state (which binds oxygen), the P-state (with an already split dioxygen bond), the F-state and the O-state again. Here, we determined structures of up to 1.9 Å resolution of these intermediates by single particle cryo-EM. Our results suggest that in the O-state the active site contains a peroxide dianion and in the P-state possibly an intact dioxygen molecule, the F-state may contain a superoxide anion. Thus, the enzyme’s catalytic cycle may have to be turned by 180 degrees.

Highlights

Cytochrome c oxidases are among the most important and fundamental enzymes of life
The oxidized binuclear centre (BNC) [O (Fea33+, CuB2+)] is reduced by the first electron leading to the appearance of the E-state (E = electronated) which is converted to an R-state [R (Fea32+, CuB+)] by further electron transfer
These results indicated that the dioxygen bond is already broken in the P-state, one oxygen atom has been bound to the heme a3-Fe via a double bond, forming an oxoferryl moiety whereas the second oxygen atom is released as water

Summary

Introduction

Cytochrome c oxidases are among the most important and fundamental enzymes of life. Integrated into membranes they use four electrons from cytochrome c molecules to reduce molecular oxygen (dioxygen) to water. In order to understand these processes, it is essential to know the structures of the intermediates of the catalytic cycle which comprises the oxidized form (O-state), the reduced CcO (R-state), the P-state (after reaction with dioxygen), the F-state and again the O-state after successive electron transfers (Fig. 1). We found densities for many dioxygen molecules in particular in the O-state CcO.

Results

Conclusion