Download MendeleyQuinone (Q(B)) Reduction by B-Branch Electron Transfer in Mutant Bacterial Reaction Centers from Rhodobacter sphaeroides: Quantum Efficiency and X-ray Structure.
Paddock, M.L., Chang, C., Xu, Q., Abresch, E.C., Axelrod, H.L., Feher, G., Okamura, M.Y.(2005) Biochemistry 44: 6920-6928
- PubMed: 15865437 Search on PubMed
- DOI: https://doi.org/10.1021/bi047559m
- Primary Citation Related Structures:
1YF6 - PubMed Abstract:
The photosynthetic reaction center (RC) from purple bacteria converts light into chemical energy. Although the RC shows two nearly structurally symmetric branches, A and B, light-induced electron transfer in the native RC occurs almost exclusively along the A-branch to a primary quinone electron acceptor Q(A). Subsequent electron and proton transfer to a mobile quinone molecule Q(B) converts it to a quinol, Q(B)H(2). We report the construction and characterization of a series of mutants in Rhodobacter sphaeroides designed to reduce Q(B) via the B-branch. The quantum efficiency to Q(B) via the B-branch Phi(B) ranged from 0.4% in an RC containing the single mutation Ala-M260 --> Trp to 5% in a quintuple mutant which includes in addition three mutations to inhibit transfer along the A-branch (Gly-M203 --> Asp, Tyr-M210 --> Phe, Leu-M214 --> His) and one to promote transfer along the B-branch (Phe-L181 --> Tyr). Comparing the value of 0.4% for Phi(B) obtained in the AW(M260) mutant, which lacks Q(A), to the 100% quantum efficiency for Phi(A) along the A-branch in the native RC, we obtain a ratio for A-branch to B-branch electron transfer of 250:1. We determined the structure of the most effective (quintuple) mutant RC at 2.25 A (R-factor = 19.6%). The Q(A) site did not contain a quinone but was occupied by the side chain of Trp-M260 and a Cl(-). In this structure a nonfunctional quinone was found to occupy a new site near M258 and M268. The implications of this work to trap intermediate states are discussed.
- Department of Physics, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA. mpaddock@physics.ucsd.edu
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