{"doi":"10.1016/j.jbc.2025.108272","title":"Structure of a mutated photosystem II complex reveals changes to the hydrogen-bonding network that affect proton egress during O–O bond formation","abstract":"Photosystem II (PSII) is the water-splitting enzyme of oxygenic photosynthesis. Using light energy, PSII catalytically oxidizes two water molecules to fuel downstream metabolism, forming an O–O bond and releasing O 2 as a byproduct. The reaction mechanism requires the strategic removal of four protons via conserved hydrogen-bonding networks, but these pathways remain poorly understood. Site-directed mutagenesis has been used to study these pathways and the role of specific side chains, such as Lys317 of the D2 subunit. Previous studies showed that the D2-Lys317Ala substitution, which abolishes the flexible hydrogen-bonding -NH 3 + group, resulted in delayed O 2 release kinetics and diminished catalytic turnover, suggesting Lys317 has a crucial role in facilitating proton egress. Here, we investigated this proton egress pathway by determining the cryo-EM structure of PSII containing the D2-Lys317Ala substitution at a resolution of 1.97 Å. We observed that four new water molecules fill the space previously occupied by Lys317, but these waters lack specific water-protein interactions, leading to heterogeneity and suboptimal hydrogen bonding. We hypothesize that these waters negatively contribute to the existing hydrogen-bonding network and increase the entropic barrier for proton transfer. Additionally, we observed that a conserved chloride ion (Cl1), which is associated with Lys317, is unexpectedly maintained in D2-Lys317Ala PSII. However, unlike in wild-type, Cl1 has no measured effect on oxygen-evolution rates in D2-Lys317Ala PSII. This suggests that the role of Cl1 is dependent on the Lys317 amino group. These findings provide new insight into proton egress through the Cl1 hydrogen-bonding channel.","journal":"Journal of Biological Chemistry","year":2025,"id":522678,"datarank":0.26606949902946003,"base_score":1.6094379124341003,"endowment":1.6094379124341003,"self_citation_contribution":0.24141568686511508,"citation_network_contribution":0.024653812164344976,"self_endowment_contribution":0.24141568686511508,"citer_contribution":0.024653812164344976,"corpus_percentile":null,"corpus_rank":null,"citation_count":4,"citer_count":3,"citers_with_citation_signal":3,"citers_with_endowment":3,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9489,"is_data_producer":true,"deposit_databanks":{"PDB":["9EH5"]},"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2025-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":1286717,"name":"Jieun Shin","orcid":"0000-0003-3817-6282","position":1,"is_corresponding":false},{"id":634425,"name":"Richard J. Debus","orcid":"0000-0003-1321-8730","position":2,"is_corresponding":false},{"id":634426,"name":"Gary W. Brudvig","orcid":"0000-0002-7040-1892","position":3,"is_corresponding":false},{"id":634422,"name":"David A. Flesher","orcid":"0000-0002-8270-4751","position":0,"is_corresponding":true}],"reference_count":50,"raw_metadata":null,"created_at":"2026-07-19T02:49:58.707747Z","pmid":"39922494","pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}