His group studies the key enzymes of photosynthesis, namely the photosynthetic reaction centre (which is a light-driven electron pump), and of aerobic respiration, namely the cytochrome c oxidase (which is a proton pump). Having completed the structure determinations of the reaction centres from the purple bacterium Rhodopseudomonas viridis and the light-harvesting complex two from a different purple bacterium, Rhodospirillum molischianum (light-harvesting complexes absorb light and transfer its energy to the reaction centres), residual activities of the group in the area of photosynthesis comprise site-directed mutagenesis of the cytochrome subunit of the Rhodopseudomonas viridis reaction centre. This work is aimed to understand the reasons for the alternate order in the cytochrome subunit of high and low potential haem groups, which are involved in the re-reduction of the primary electron donor.
The main current objective is to understand the mechanism of action of cytochrome c oxidases, based on an accurately known structure, especially how electron transfer is coupled to proton pumping across the membrane. For the purpose of membrane protein crystallization and subsequent structure determination a novel method consisting in co-crystallization with Fv-fragments of monoclonal antibodies has been developed, and used to crystallize two different cytochrome c oxidase preparations from the soil bacterium Paracoccus denitrificans. After the subsequent structure determination by X-ray crystallography the resulting coordinate set has been used for theoretical calculations, e.g. to study computationally protonation changes upon reduction of cytochrome c oxidase.
In a collaborative effort with the group of W. Mäntele (Institute of Biophysics, Frankfurt University) Fourier transform infrared spectroscopy, partly on 13C-labeled
enzyme, was used for the same purpose. Based on the resulting data, and a critical reanalysis of literature data, a detailed mechanistic model of proton pumping has been proposed.
Biophysics Prize of the American Physical Society (together with d. Deisenhofer),
"Chemiedozentenstipendium" of the "Fonds der Chemischen Industrie"
"Otto Klung-Preis" for chemistry,
Leibniz-Preis of the Deutsche Forschungsgemeinschaft,
"Otto-Bayer-Preis" (together with J. Deisenhofer)
1998 Nobel Prize (together with J. Deisenhofer and R. Huber) for the determination of the three-dimensional structure of a photosynthetic reaction centre.
Ostermeier, C., Iwata, S., Ludwig, B., and Michel, H.: Fv Fragment-mediated crystallization of the membrane protein bacterial cytochrome c oxidase. Nature Struct. Biol. 2, 842-846 (1995).
Ostermeier, C, Harrenga, A., Ermler, U., and Michel, H.: Structure at 2.7 Å resolution of the Paracoccus denitrificans two-subunit cytochrome c oxidase complexed with an antibody Fv fragment. Proc. Natl. Acad. Sci. USA 94, 10547-10553 (1997).
Michel, H.: The mechanism of proton pumping by cytochrome c oxidase. Proc. Natl. Acad. Sci. USA 95, 12819-12842 (1998).