Primary charge separation between P* and BA: Electron-transfer pathways in native and mutant GM203L bacterial reaction centers

被引:33
作者
Yakovlev, AG
Jones, MR [1 ]
Potter, JA
Fyfe, PK
Vasilieva, LG
Shkuropatov, AY
Shuvalov, VA
机构
[1] Moscow MV Lomonosov State Univ, Dept Photobiophys, Belozersky Inst Chem & Phys Biol, Moscow 119899, Russia
[2] Univ Bristol, Sch Med Sci, Dept Biochem, Bristol BS8 1TD, Avon, England
[3] Russian Acad Sci, Inst Basic Biol Problems, Pushchino 142290, Moscow, Russia
基金
英国生物技术与生命科学研究理事会; 俄罗斯基础研究基金会;
关键词
protein dynamics; electron transfer; reaction center; nuclear coherence; water; bacteriochlorophyll;
D O I
10.1016/j.chemphys.2005.08.018
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Coherent components in the dynamics of decay of stimulated emission from the primary electron donor excited state P*, and of population of the product charge-separated states P+BA- and P+HA-, were studied in GM203L mutant reaction centers (RCs) of Rhodobacter (Rb.) sphaeroides by measuring oscillations in the kinetics of absorbance changes at 940 nm (P* stimulated emission region), 1020 nm (BA absorption region) and 760 nm (HA bleaching region). Absorbance changes were induced by excitation of P (870 nm) with 18 fs pulses at 90 K. In the GM203L mutant, replacement of Gly M203 by Leu results in exclusion of the crystallographically defined water molecule (HOH55) located close to the oxygen of the 13(1)-keto carbonyl group of B-A and to His M202, which provides the axial ligand to the Mg of the P-B bacteriochlorophyll. The results of femtosecond measurements were compared with those obtained with Rb. sphaeroides R-26 RCs containing an intact water HOH55. The main consequences of the GM203L mutation were found to be as follows: (i) a low-frequency oscillation at 32 cm(-1), which is characteristic of the HOH55-containing RCs, disappears from the kinetics of absorbance changes at 1020 and 760 nm in the mutant RC; (ii) electron transfer from P* to B-A in the wild type RC was characterized by two time constants of 1.1 ps (80%) and 4.3 ps (20%), but in the GM203L mutant was characterized by a single time constant of 4.3 ps, demonstrating a slowing of primary charge separation. The previously postulated rotation of water HOH55 with a fundamental frequency of 32 cm(-1), triggered by electron transfer from P* to BA, was confirmed by observation of an isotopic shift of the 32 cm(-1) oscillation in the kinetics of P+BA- population in deuterated, pheophytin-modified RCs of Rb. sphaeroides R-26, by a factor of 1.6. These data are discussed in terms of the influence of water HOH55 on the energetics of the P* -> P+BA- reaction, and protein dynamic events that occur on the time scale of this reaction. (c) 2005 Elsevier B.V. All rights reserved.
引用
收藏
页码:297 / 307
页数:11
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