Glycerol binding at the narrow channel of photosystem II stabilizes the low-spin S2 state of the oxygen-evolving complex.

Autor: Flesher, David A., Liu, Jinchan, Wiwczar, Jessica M., Reiss, Krystle, Yang, Ke R., Wang, Jimin, Askerka, Mikhail, Gisriel, Christopher J., Batista, Victor S., Brudvig, Gary W.
Zdroj: Photosynthesis Research; May2022, Vol. 152 Issue 2, p167-175, 9p
Abstrakt: 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. 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. [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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