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Published November 1, 1988 | Published
Journal Article Open

Structure of the Reaction Center from Rhodopseudomonas sphaeroides R-26 and 2.4.1: Protein-Cofactor (Bacteriochlorophyll, Bacteriopheophytin and Carotenoid) Interactions

Abstract

The three-dimensional structures of the cofactors and protein subunits of the reaction center (RC) from the carotenoidless mutant strain of Rhodobacter sphaeroides R-26 and the wild-type strain 2.4.1 have been determined by x-ray diffraction to resolutions of 2.8 Å and 3.0 Å with R values of 24% and 26%, respectively. The bacteriochlorophyll dimer (D), bacteriochlorophyll monomers (B), and bacteriopheophytin monomers (φ) form two branches, A and B, that are approximately related by a twofold symmetry axis. The cofactors are located in hydrophobic environments formed by the L and M subunits. Differences in the cofactor-protein interactions between the A and B cofactors, as well as between the corresponding cofactors of Rb, sphaeroides and Rhodopseudomonas viridis [Michel, H., Epp, O. & Deisenhofer, J. (1986) EMBO J. 3, 2445-2451], are delineated. The roles of several structural features in the preferential electron transfer along the A branch are discussed. Two bound detergent molecules of beta-octyl glucoside have been located near B_A and B_B. The environment of the carotenoid, C, that is present in RCs from Rb. sphaeroides 2.4.1 consists largely of aromatic residues of the M subunit. A role of B_B in the triplet energy transfer from D to C and the reason for the preferential ease of removal of B_B from the RC is proposed.

Additional Information

© 1988 National Academy of Sciences. Contributed by G. Feher, July 22, 1988. We thank E. Abresch for the preparation of the RCs and M. Y. Okamura and W. Lubitz for helpful discussions. This work was supported by grants from the National Institutes of Health (AM36053, GM13191, GM31875), the National Science Foundation (DMB85-18922), and a Presidential Young Investigators Award. D.C.R. is an A. P. Sloan research fellow. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

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