W0301

X-Ray Structures of the Cytochrome Bc₁ Complex: From Antibodies to Membrane Protein Structure. Carola Hunte, Hildur Palsdottir, Sozanne Solmaz, Christian Lange, Max-Planck-Institute of Biophysics, Dept. Molecular Membrane Biology, Frankfurt, Germany, Carola.Hunte@mpibp-frankfurt.mpg.de

The cytochrome bc₁ complex (ubiquinol:cytochrome c oxidoreductase, QCR) is a multisubunit membrane protein, which couples electron transfer to translocation of protons across the inner mitochondrial membrane, thereby contributing to the electrochemical proton gradient. The molecular mechanism of the enzyme, known as modified Q cycle, is still not fully understood. A central question is the bifurcation of the electron transfer pathway upon quinol oxidation at the Qo site.

Structures of yeast QCR at high resolution revealed details of the catalytic sites elucidating aspects of electron and proton transfer [1]. Tightly bound phospholipid molecules appear to be important for structural and functional integrity of the complex [2]. Furthermore, we determined the structure of the complex between yeast QCR and cytochrome c, which is critical for intermolecular electron transfer [3]. Crystallization of yeast QCR has been achieved with specifically binding antibody fragments. The prospects of this technique will be discussed.

[1] C. Hunte et al., Structure Fold Des 8, 669, (2000)

[2] C. Lange et al. & C. Hunte, EMBO J. 20, 6591-660, (2001)

[3] C. Lange and C. Hunte, Proc. Natl. Acad. Sci. USA 99, 2800, (2002)