Electron transfer between spinach plastocyanin mutants and photosystem 1.
Two distinct regions of plastocyanin, one hydrophobic and one acidic, are generally thought to be involved in the electron-transfer reactions with its physiological partners, cytochrome f and photosystem 1. To probe the importance of the hydrophobic patch in the reaction with photosystem 1, seven mutant plastocyanin proteins have been constructed with the following mutations: Gly7Ala, Gly8Asp, Ser11Asp, Ser11Gly, Pro36Gly, Ser85Thr and Gln88Asn. The electron-transfer reaction was investigated by transient flash-photolysis absorption spectroscopy. All proteins remained active in photosystem 1 reduction, showing a biphasic reaction. However, the substitution in position 36 resulted in a drastic decrease in efficiency, suggesting that this residue is involved in a specific contact with photosystem 1. Measurements over a wide range of plastocyanin concentration, ionic strength and pH, showed different properties for the two kinetic phases. A mechanism involving a rate-limiting conformational change accounts well for the observations. Electron transfer from plastocyanin to photosystem 1 would thus require a conversion from an inactive to an active conformation of the complex. Both hydrophobic and electrostatic interactions are important in the dynamics. The structural integrity of a few critical residues, including Pro36, is essential for efficient photosystem 1 reduction.
Sigfridsson
K
K
Department of Biochemistry and Biophysics, Göteborg University and Chalmers University of Technology, Sweden.
Young
S
S
Hansson
O
O
D004579:Electron Transport; D007700:Kinetics; D009154:Mutation; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D010970:Plastocyanin / Q000235:genetics / Q000378:metabolism*; D018724:Spinacia oleracea / Q000378:metabolism*
D045322:Photosynthetic Reaction Center Complex Proteins; D010970:Plastocyanin