Probing the role of arginine 323 of the D1 protein in photosystem II function

Abstract

The Mn4CaO5 cluster of photosystem II (PSII) advances sequentially through five oxidation states (S0 to S4). Under the enzyme cycle, two water molecules are oxidized, O2 is generated and four protons are released into the lumen. Umena et al. (2011) have proposed that, with other charged amino acids, the R323 residue of the D1 protein could contribute to regulate a proton egress pathway from the Mn4CaO5 cluster and TyrZ via a proton channel identified from the 3D structure. To test this suggestion, a PsbA3/R323E site‐directed mutant has been constructed and the properties of its PSII have been compared to those of the PsbA3‐PSII by using EPR spectroscopy, polarography, thermoluminescence and time‐resolved UV–visible absorption spectroscopy. Neither the oscillations with a period four nor the kinetics and S‐state‐dependent stoichiometry of the proton release were affected. However, several differences have been found: (1) the P680+ decay in the hundreds of ns time domain was much slower in the mutant, (2) the S2QA−/DCMU and S3QA−/DCMU radiative charge recombination occurred at higher temperatures and (3) the S0TyrZ•, S1TyrZ•, S2TyrZ• split EPR signals induced at 4.2 K by visible light from the S0TyrZ, S1TyrZ, S2TyrZ, respectively, and the (S2TyrZ•)' induced by NIR illumination at 4.2 K of the S3TyrZ state differed. It is proposed that the R323 residue of the D1 protein interacts with TyrZ likely via the H‐bond network previously proposed to be a proton channel. Therefore, rather than participating in the egress of protons to the lumen, this channel could be involved in the relaxations of the H‐bonds around TyrZ by interacting with the bulk, thus tuning the driving force required for TyrZ oxidation.

Probing the proton release by Photosystem II in the S1 to S2 high-spin transition

“…In PSII/Ca, at pH 6.0 (Panel A in Fig. 4), the kinetics were very similar to those already described at pH 6.3 [67]. After the first flash, the increase in the ΔI/I with a t 1/2 close to 300 µs corresponds to the proton uptake following the reduction of the non-heme iron by Q A - which occurs with a t 1/2 ∼ 50 µs [10].…”

“…However, the drift may slightly decrease the amplitude of the slower phase in the S 3 to S 0 transition. The ΔI/I changes observed between 5 µs and 10 µs, likely due electrostatic effects on the dyes [73], were previously discussed [65].…”

“…In the analysis of such experiments, the data from the first flash are usually discarded due to several non-oscillating contributions [63]. In previous works, we did not consider that the non-heme iron could contribute after the first flash [67,69,71]. The data in Panel A and C in Fig.…”

“…The pH was adjusted with NaOH. The measurements with the dyes were done as previously reported [65, 67]. In this case, the samples were diluted in 1 M betaine, 15 mM CaCl 2 , 15 mM MgCl 2 , and either 150 µM bromocresol purple at pH 6.0 or 40 µM neutral red adjusted at pH 7.0.…”

Biomimicking Hydrogen-Bonding Network by Ammoniated and Hydrated Manganese (II) Phosphate for Electrocatalytic Water Oxidation

“…Two water molecules are connected to the Ca atom and the Mn atom outside the deformed cube, respectively 31 . In addition to water molecules, there are many amino acid residues around the CaMn4O5 cluster 16,[32][33][34] . Water molecules and these amino acid residues are connected to the CaMn4O5 cluster by hydrogen bonds, which can not only stabilize the structure of the CaMn4O5 cluster, but also play an important role in OER process 35 .…”