Conformational changes in the cytochrome b6f complex induced by inhibitor binding

Abstract

Binding of stigmatellin, an inhibitor of the Q(o) site of the bc-type complexes, has been shown to induce large conformational changes of the Rieske protein in the respiratory bc1 complex (Kim, H., Xia, D., Yu, C. A., Xia, J. Z., Kachurin, A. M., Zhang, L., Yu, L., and Deisenhofer, J. (1998) Proc. Natl. Acad. Sci. U.S.A. 95, 8026-8033; Iwata, S., Lee, J. W., Okada, K., Lee, J. K., Iwata, M., Rasmussen, B., Link, T. A., Ramaswamy, S., and Jap, B. K. (1998) Science 281, 64-71; Zhang, Z., Huang, L., Shulmeister, V. M., Chi, Y. I., Kim, K. K., Hung, L. W., Crofts, A. R., Berry, E. A., and Kim, S. H. (1998) Nature 392, 677-684). Such a movement seems necessary to shuttle electrons from the membrane-soluble quinol to the extramembrane heme of cytochrome c1. To see whether similar changes occur in the related photosynthetic b6f complex, we have studied the effect of the binding of stigmatellin to the eukaryotic b6f complex by electron crystallography. Comparison of projection maps of thin three-dimensional crystals prepared with or without stigmatellin, and either negatively stained or embedded in glucose, reveals a similar type of movement to that observed in the bc1 complex and suggests also the occurrence of conformational changes in the transmembrane region.