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X-ray Structure Determination of the Cytochrome c_2: Reaction Center Electron Transfer Complex from Rhodobacter sphaeroides

Axelrod, Herbert L. and Abresch, Edward C. and Okamura, Melvin Y. and Yeh, Andrew P. and Rees, Douglas C. and Feher, George (2002) X-ray Structure Determination of the Cytochrome c_2: Reaction Center Electron Transfer Complex from Rhodobacter sphaeroides. Journal of Molecular Biology, 319 (2). pp. 501-515. ISSN 0022-2836.

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In the photosynthetic bacterium Rhodobacter sphaeroides, a water soluble cytochrome c_2 (cyt c_2) is the electron donor to the reaction center (RC), the membrane-bound pigment–protein complex that is the site of the primary light-induced electron transfer. To determine the interactions important for docking and electron transfer within the transiently bound complex of the two proteins, RC and cyt c_2 were co-crystallized in two monoclinic crystal forms. Cyt c_2 reduces the photo-oxidized RC donor (D+), a bacteriochlorophyll dimer, in the co-crystals in ∼0.9 μs, which is the same time as measured in solution. This provides strong evidence that the structure of the complex in the region of electron transfer is the same in the crystal and in solution. X-ray diffraction data were collected from co-crystals to a maximum resolution of 2.40 Å and refined to an R-factor of 22% (R_(free)=26%). The structure shows the cyt c_2 to be positioned at the center of the periplasmic surface of the RC, with the heme edge located above the bacteriochlorophyll dimer. The distance between the closest atoms of the two cofactors is 8.4 Å. The side-chain of Tyr L162 makes van der Waals contacts with both cofactors along the shortest intermolecular electron transfer pathway. The binding interface can be divided into two domains: (i) A short-range interaction domain that includes Tyr L162, and groups exhibiting non-polar interactions, hydrogen bonding, and a cation–π interaction. This domain contributes to the strength and specificity of cyt c_2 binding. (ii) A long-range, electrostatic interaction domain that contains solvated complementary charges on the RC and cyt c_2. This domain, in addition to contributing to the binding, may help steer the unbound proteins toward the right conformation.

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Rees, Douglas C.0000-0003-4073-1185
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Additional Information:© 2002 Elsevier Science Ltd. Received 28 November 2001; received in revised form 18 February 2002; accepted 25 February 2002. We thank R. Isaacson for his expert help in designing and running the microspectrophotometer, Keith Henderson at the Advanced Light Source (ALS), and the staff at the Stanford Synchrotron Radiation Laboratory (SSRL) for their advice and assistance with the X-ray data collections; Mark Paddock, Raphael Calvo, Les Dutton, Marilyn Gunner, and Jose Onuchic for helpful discussions. The synchrotron X-ray data collection facilities are supported by the U.S. Department of Energy (ALS, SSRL) and NIH (SSRL). This work was supported by the National Institutes of Health (grant number GM-13191 to G. F. and GM-45162 to D. C. R.) and National Science Foundation (grant number 9974568 to M.Y.O.).
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Department of Energy (DOE)UNSPECIFIED
Subject Keywords:bacterial photosynthesis; protein-protein interaction; electron transfer proteins; membrane proteins; protein complexes
Issue or Number:2
Record Number:CaltechAUTHORS:20150108-152754099
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Official Citation:Herbert L. Axelrod, Edward C. Abresch, Melvin Y. Okamura, Andrew P. Yeh, Douglas C. Rees, George Feher, X-ray Structure Determination of the Cytochrome c2: Reaction Center Electron Transfer Complex from Rhodobacter sphaeroides, Journal of Molecular Biology, Volume 319, Issue 2, 31 May 2002, Pages 501-515, ISSN 0022-2836, (
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ID Code:53399
Deposited By: SWORD User
Deposited On:08 Feb 2015 06:43
Last Modified:03 Oct 2019 07:49

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