Changes in structural and functional properties of oxygen-evolving complex induced by replacement of D1-glutamate 189 with glutamine in photosystem II: ligation of glutamate 189 carboxylate to the manganese cluster.

A carboxylate group of D1-Glu-189 in photosystem II has been proposed to serve as a direct ligand for the manganese cluster. Here we constructed a mutant that eliminates the carboxylate by replacing D1-Glu-189 with Gln in the cyanobacterium Synechocystis sp. PCC 6803, and we examined the resulting effects on the structural and functional properties of the oxygen-evolving complex (OEC) in photosystem II. The E189Q mutant grew photoautotrophically, and isolated photosystem II core particles evolved oxygen at approximately 70% of the rate of control wild-type particles. The E189Q OEC showed typical S(2) state electron spin resonance signals, and the spin center distance between the S(2) state manganese cluster and the Y(D) (D2-Tyr-160), detected by electron-electron double resonance spectroscopy, was not affected by this mutation. However, the redox potential of the E189Q OEC was considerably lower than that of the control OEC, as revealed by the elevated peak temperature of the S(2) state thermoluminescence bands. The mutation resulted in specific changes to bands ascribed to the putative carboxylate ligands for the manganese cluster and to a few carbonyl bands in mid-frequency (1800 to 1100 cm(-1)) S(2)/S(1) Fourier transform infrared difference spectrum. Notably, the low frequency (650 to 350 cm(-1)) S(2)/S(1) Fourier transform infrared difference spectrum was also uniquely changed by this mutation in the frequencies for the manganese cluster core vibrations. These results suggested that the carboxylate group of D1-Glu-189 ligates the manganese ion, which is influenced by the redox change of the oxidizable manganese ion upon the S(1) to S(2) transition.