Glycerol Binding at the Narrow Channel of Photosystem II Stabilizes the Low-Spin S2 State of the Oxygen-Evolving Complex
Journal Article
·
· Photosynthesis Research
- Yale Univ., New Haven, CT (United States); Yale University
- Yale Univ., New Haven, CT (United States)
The oxygen-evolving complex (OEC) of photosystem II (PSII) cycles through redox intermediate states Si (i = 0–4) during the photochemical oxidation of water. The S2 state involves an equilibrium of two isomers including the low-spin S2 (LS-S2) state with its characteristic electron paramagnetic resonance (EPR) multiline signal centered at g = 2.0, and a high-spin S2 (HS-S2) state with its g = 4.1 EPR signal. The relative intensities of the two EPR signals change under experimental conditions that shift the HS-S2/LS-S2 state equilibrium. Here, we analyze the effect of glycerol on the relative stability of the LS-S2 and HS-S2 states when bound at the narrow channel of PSII, as reported in an X-ray crystal structure of cyanobacterial PSII. Our quantum mechanics/molecular mechanics (QM/MM) hybrid models of cyanobacterial PSII show that the glycerol molecule perturbs the hydrogen-bond network in the narrow channel, increasing the pKa of D1-Asp61 and stabilizing the LS-S2 state relative to the HS-S2 state. Here, the reported results are consistent with the absence of the HS-S2 state EPR signal in native cyanobacterial PSII EPR spectra and suggest that the narrow water channel hydrogen-bond network regulates the relative stability of OEC catalytic intermediates during water oxidation.
- Research Organization:
- Yale Univ., New Haven, CT (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division
- Grant/Contract Number:
- FG02-05ER15646; SC0001423
- OSTI ID:
- 1860621
- Journal Information:
- Photosynthesis Research, Journal Name: Photosynthesis Research Journal Issue: 2 Vol. 152; ISSN 0166-8595
- Publisher:
- SpringerCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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