The D1-V185N mutation alters substrate water exchange by stabilizing alternative structures of the Mn4Ca-cluster in photosystem II

• Published in: Biochimica et biophysica acta. Bioenergetics 2021-01, Vol.1862 (1), p.148319, Article 148319
• Main Authors: de Lichtenberg, Casper, Avramov, Anton P., Zhang, Minquan, Mamedov, Fikret, Burnap, Robert L., Messinger, Johannes
• Format: Article
• Language: English
• Subjects: EPR; Manganese cluster; O-O bond formation; Photosystem II; Substrate water exchange; Water oxidation
• ISSN: 0005-2728; 1879-2650
• DOI: 10.1016/j.bbabio.2020.148319

In photosynthesis, the oxygen-evolving complex (OEC) of the pigment-protein complex photosystem II (PSII) orchestrates the oxidation of water. Introduction of the V185N mutation into the D1 protein was previously reported to drastically slow O2-release and strongly perturb the water network surrounding the Mn4Ca cluster. Employing time-resolved membrane inlet mass spectrometry, we measured here the H218O/H216O-exchange kinetics of the fast (Wf) and slow (Ws) exchanging substrate waters bound in the S1, S2 and S3 states to the Mn4Ca cluster of PSII core complexes isolated from wild type and D1-V185N strains of Synechocystis sp. PCC 6803. We found that the rate of exchange for Ws was increased in the S1 and S2 states, while both Wf and Ws exchange rates were decreased in the S3 state. Additionally, we used EPR spectroscopy to characterize the Mn4Ca cluster and its interaction with the redox active D1-Tyr161 (YZ). In the S2 state, we observed a greatly diminished multiline signal in the V185N-PSII that could be recovered by addition of ammonia. The split signal in the S1 state was not affected, while the split signal in the S3 state was absent in the D1-V185N mutant. These findings are rationalized by the proposal that the N185 residue stabilizes the binding of an additional water-derived ligand at the Mn1 site of the Mn4Ca cluster via hydrogen bonding. Implications for the sites of substrate water binding are discussed. •Synechocystis PCC 6803 WT PSII and V185N PSII were compared by TR-MIMS and EPR.•Both substrate waters are manganese bound in the S3 state.•The V185N mutation stabilizes water bound conformations of the Mn4Ca-cluster.