Complete Structure of the 11-Subunit Bovine Mitochondrial Cytochrome bc ₁ Complex

TLDR

Mitochondrial cytochrome bc₁ complex is a respiratory multienzyme complex that also recognizes a mitochondrial targeting presequence. Refined crystal structures of the bovine 11‑subunit bc₁ complex reveal its full architecture, show Rieske subunit conformational changes implying a new electron‑transport mechanism, and illustrate how the Rieske presequence is lodged between core subunits related to matrix processing peptidase, thereby revealing presequence recognition.

Abstract

Mitochondrial cytochrome bc 1 complex performs two functions: It is a respiratory multienzyme complex and it recognizes a mitochondrial targeting presequence. Refined crystal structures of the 11-subunit bc 1 complex from bovine heart reveal full views of this bifunctional enzyme. The “Rieske” iron-sulfur protein subunit shows significant conformational changes in different crystal forms, suggesting a new electron transport mechanism of the enzyme. The mitochondrial targeting presequence of the “Rieske” protein (subunit 9) is lodged between the two “core” subunits at the matrix side of the complex. These “core” subunits are related to the matrix processing peptidase, and the structure unveils how mitochondrial targeting presequences are recognized.