Symmetry-related mutants in the quinone binding sites of the reaction center -- The effects of changes in charge distribution

Technical Report · Mon Sep 01 04:00:00 EDT 1997

DOI:https://doi.org/10.2172/563250· OSTI ID:563250

Hanson, D K; Schiffer, M ^[1]

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1. Argonne National Lab., IL (United States). Center for Mechanistic Biology and Biotechnology

To probe the structural elements that contribute to the functional asymmetries of the two ubiquinone{sub 10}binding pockets in the reaction center of Rhodobacter capsulatus, the authors targeted the L212Glu-L213Asp (near Q{sub B}) and the M246Ala-M247Ala (near Q{sub A}) pairs of symmetry-related residues for site-specific mutagenesis. They have constructed site-specific mutants that eliminate the sequence differences at these positions (L212Glu-L213Asp{yields}Ala-Ala or M246Ala-M247Ala{yields}Glu-Asp), and have reversed that asymmetry by constructing a quadruple-mutant strain, RQ (L212Glu-L213Asp-M246Ala-M247Ala{yields}Ala-Ala-Glu-Asp). The mutations were designed to change the charge distribution in the quinone-binding region of the reaction center; none of the strains is capable of photosynthetic growth. In photocomponent phenotypic revertants of the RQ strain, second-site mutations which affect Q{sub B} function are coupled to mutations in the Q{sub A} site which restore an Ala or substitute a Tyr at the M247 site; one strain carries an additional Met{yields}Glu substitution at M260 near Q{sub A}. All of the RQ revertants retain the engineered M246Ala{yields}Glu mutation in the Q{sub A} site as well as the L212Ala-L213Ala mutations in the Q{sub B} site. Kinetic characterization of the RQ revertants will give them an idea of what structural and functional elements are important for restoring efficiency to electron and proton transfer pathways in the RQRC, which is far from native. To date, these preliminary results underscore the importance of an asymmetric distribution of polar amino acids in the quinone binding pockets and its influence on the functional properties of the reaction center.

• Research Organization: Argonne National Lab., IL (United States)
• Sponsoring Organization: USDOE Office of Administration and Human Resource Management, Washington, DC (United States)
• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 563250
• Report Number(s): ANL/CMB/CP--94237; CONF-9706202--; ON: DE97054049
• Country of Publication: United States
• Language: English

Related Subjects

55 BIOLOGY AND MEDICINE
BASIC STUDIES
BIOCHEMICAL REACTION KINETICS
EXPERIMENTAL DATA
MOLECULAR STRUCTURE
MUTAGENESIS
PHENOTYPE
PHOTOSYNTHESIS
PHOTOSYNTHETIC BACTERIA
PHOTOSYNTHETIC REACTION CENTERS
RECEPTORS
UBIQUINONE