title: Alpha-helices direct excitation energy flow in the Fenna Matthews Olson protein.
abstract: In photosynthesis, light is captured by antenna proteins. These proteins transfer the excitation energy with almost 100% quantum efficiency to the reaction centers, where charge separation takes place. The time scale and pathways of this transfer are controlled by the protein scaffold, which holds the pigments at optimal geometry and tunes their excitation energies (site energies). The detailed understanding of the tuning of site energies by the protein has been an unsolved problem since the first high-resolution crystal structure of a light-harvesting antenna appeared >30 years ago [Fenna RE, Matthews BW (1975) Nature 258:573-577]. Here, we present a combined quantum chemical/electrostatic approach to compute site energies that considers the whole protein in atomic detail and provides the missing link between crystallography and spectroscopy. The calculation of site energies of the Fenna-Matthews-Olson protein results in optical spectra that are in quantitative agreement with experiment and reveals an unexpectedly strong influence of the backbone of two alpha-helices. The electric field from the latter defines the direction of excitation energy flow in the Fenna-Matthews-Olson protein, whereas the effects of amino acid side chains, hitherto thought to be crucial, largely compensate each other. This result challenges the current view of how energy flow is regulated in pigment-protein complexes and demonstrates that attention has to be paid to the backbone architecture.
authors.affiliation: Institute for Chemistry and Biochemistry (Crystallography), Free University of Berlin, Takustrasse 6, 14195 Berlin, Germany. mueh@chemie.fu-berlin.de
authors.forename: Frank
authors.initials: F
authors.lastname: Müh
authors.forename: Mohamed El-Amine
authors.initials: Mel-A
authors.lastname: Madjet
authors.forename: Julia
authors.initials: J
authors.lastname: Adolphs
authors.forename: Ayjamal
authors.initials: A
authors.lastname: Abdurahman
authors.forename: Björn
authors.initials: B
authors.lastname: Rabenstein
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ishikita
authors.forename: Ernst-Walter
authors.initials: EW
authors.lastname: Knapp
authors.forename: Thomas
authors.initials: T
authors.lastname: Renger
mesh_terms: D019414:Chlorobi / Q000737:chemistry*; D002942:Circular Dichroism; D003198:Computer Simulation; D004735:Energy Transfer; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism; D010860:Pigments, Biological / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D010860:Pigments, Biological