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TitleStructure of a mutated photosystem II complex reveals changes to the hydrogen-bonding network that affect proton egress during O-O bond formation.
Journal, issue, pagesJ Biol Chem, Vol. 301, Issue 3, Page 108272, Year 2025
Publish dateFeb 6, 2025
AuthorsDavid A Flesher / Jieun Shin / Richard J Debus / Gary W Brudvig /
PubMed AbstractPhotosystem 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 ...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 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 group, resulted in delayed O 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.
External linksJ Biol Chem / PubMed:39922494 / PubMed Central
MethodsEM (single particle)
Resolution1.97 Å
Structure data

48046

9eh5

EMDB-48046, PDB-9eh5:
Structure of a mutated photosystem II complex reveals changes to the hydrogen-bonding network that affect proton egress during O-O bond formation
Method: EM (single particle) / Resolution: 1.97 Å

Chemicals

ChemComp-OEX:
CA-MN4-O5 CLUSTER

ChemComp-FE2:
Unknown entry

ChemComp-CL:
Unknown entry

ChemComp-CLA:
CHLOROPHYLL A

ChemComp-PHO:
PHEOPHYTIN A

ChemComp-BCR:
BETA-CAROTENE

ChemComp-LMG:
1,2-DISTEAROYL-MONOGALACTOSYL-DIGLYCERIDE

ChemComp-PL9:
2,3-DIMETHYL-5-(3,7,11,15,19,23,27,31,35-NONAMETHYL-2,6,10,14,18,22,26,30,34-HEXATRIACONTANONAENYL-2,5-CYCLOHEXADIENE-1,4-DIONE-2,3-DIMETHYL-5-SOLANESYL-1,4-BENZOQUINONE

ChemComp-SQD:
1,2-DI-O-ACYL-3-O-[6-DEOXY-6-SULFO-ALPHA-D-GLUCOPYRANOSYL]-SN-GLYCEROL

ChemComp-LMT:
DODECYL-BETA-D-MALTOSIDE / detergent*YM

ChemComp-BCT:
BICARBONATE ION / pH buffer*YM

ChemComp-LHG:
1,2-DIPALMITOYL-PHOSPHATIDYL-GLYCEROLE / phospholipid*YM

ChemComp-DGD:
DIGALACTOSYL DIACYL GLYCEROL (DGDG)

ChemComp-HEM:
PROTOPORPHYRIN IX CONTAINING FE

ChemComp-RRX:
(3R)-beta,beta-caroten-3-ol

ChemComp-CA:
Unknown entry

ChemComp-HOH:
WATER

Source
  • synechocystis sp. pcc 6803 (bacteria)
KeywordsPHOTOSYNTHESIS / photosystem II / oxygen-evolving complex / transition metals / metalloenzyme / mutagenesis / water channel / hydrogen-bond network

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