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Abstract

Electron crystallography of the chloroplastic b₆f complex allowed the calculation of projection maps of crystals negatively stained or embedded in glucose. This gives insights into the overall structure of the extra- and transmembrane domains of the complex. A comparison with the structure of the bc₁ complex, the mitochondrial homologue of the b₆f complex, suggests that the transmembrane domains of the two complexes are very similar, confirming the structural homology deduced from sequence analysis. On the other hand, the extramembrane organisation of the c-type cytochrome and of the Rieske protein seems quite different. Nevertheless, the same type of movement of the Rieske protein is observed in the b₆f as in the bc₁ complex upon the binding of the quinol analogue stigmatellin. Crystallographic data also suggest movements in the transmembrane domains of the b₆f complex, which would be specific of the b₆f complex.