Fenna-Matthews-Olson complex



The Fenna-Matthews-Olson (FMO) complex is a water soluble complex and was the first pigment-protein complex (PPC) that has been structure analyzed by x-ray spectroscopy [Fenna & Matthews, 1975]. It appears in green sulfur bacteria and mediates the excitation energy transfer from the light-harvesting chlorosomes to the membrane embedded bacterial reaction center (bRC). The structure of the FMO complex is trimeric (C3-symmetry) and each of the three monomers contains seven bacteriochlorophyll a (BChl a) molecules, which are bound to the protein scaffold via ligation of their central magnesium atom either to amino acids of the protein (mostly histidine) or water-bridged oxygen atoms (only one BChl a of each monomer). Since the structure of the FMO complex is available, one can try to calculate structure based optical spectra in comparism with experimental optical spectra [Vulto et al. 1998; Wendling et al. 2002]. In the simplest case only the excitonic coupling of the BChls is taken into account [Pearlstein, 1992], while more realistic theories also consider the pigment-protein coupling [Renger & Marcus, 2002]. A very important property is the local transition energy (site energy) of the BChls, which is different for each of them, due to their individual local protein invironment. The site energies of the BChls determine the direction of the energy flow. There is some structural information on the FMO-RC super complex available, which has been obtained by electron microscopy [Remigy et al., 1999 & 2002] and linear dicroism spectra measured on FMO trimers and FMO-RC complexes. From these measurements, two possible orientations of the FMO complex relative to the RC are possible. Recently it was possible to decide which of the one orientations is useful for efficient energy transfer [Adolphs & Renger, 2006], namly the orientation with BChl 3 and 4 close to the RC and BChl 1 and 6 (numbering according to the original numbering of Fenna and Matthews) oriented towards the chlorosomes.

The FMO complex remains an interesting object for studies, because it is the simplest PPC appearing in nature and therefore a suitable test object for the development of methods, that can be transferred on more complex systems like photosystem I.

References

Adolphs, J. and Renger, T. (2006). Biophys. J. 91, 2778-2797.

Fenna, R.E. and Matthews, B.W. (1975). Nature, 258, 573-577.

Pearlstein, R.M. (1992). Photosynth. Res. 31, 213-226.

Remigy, H.W., Stahlberg, H., Fotiadis, D., Wolpensinger, B., Engel, A., Hauska, G., Tsiotis, G. (1999). J. Mol. Biol. 290, 851-858.

Remigy, H.W., Hauska, G., Müller, S.A., Tsiotis, G. (2002). Photosynth. Res. 71, 91-98.

Renger, T. and Marcus, R.A. (2002). J. Chem. Phys. 116, 9997-10019.

Vulto, S.I.E., Neerken, S., Louwe, R.J.W., de Baat, M.A., Amesz, J., Aartsma, T.J. (1998). J. Phys. Chem. B. 102, 10630-10635.

Wendling, M., Gülen, D., Vulto, S.I.E., Aartsma, T. J., van Grondelle, R., van Amerongen, H. (2002). Photosynth. Res. 71, 99-123.