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Water Bridges Conduct Sequential Proton Transfer in Photosynthetic Oxygen Evolution.
J Phys Chem B. 2019 05 30; 123(21):4487-4496.JP

Abstract

Proton transfer using water bridges has been observed in bulk water, acid-base reactions, and several proton-translocating biological systems. In the photosynthetic water-oxidizing enzyme, photosystem II (PSII), protons from substrate water are transferred 35 Å from the Mn4CaO5 catalytic site to the chloroplast lumen. This process leads to acidification of the lumen and ATP synthesis. Water oxidation occurs in a flash-induced, five-step S n state cycle; acetate is a chloride-dependent inhibitor of the S2 to S3 step of this cycle. Here, we study the effect of acetate on a previous step of the cycle, the S1 to S2 transition, using reaction-induced infrared spectroscopy. PSII was isolated from spinach, and experiments were conducted at pH 7.5, using 532 nm laser flashes to advance the cycle from the dark-adapted state S1 to the S2 state. Isotope-editing of acetate reveals direct contributions to the S2-minus-S1 infrared spectrum consistent with protonation of bound acetate in PSII. In the acetate-derived S2-minus-S1 PSII spectra, an accompanying decrease in the intensity of a 2830 cm-1 band is observed when compared to the chloride control. The 2830 cm-1 band has been assigned previously to a stretching vibration of an internal, hydrated hydronium ion, W n+. Density functional studies of a catalytic site model predict the spontaneous transfer of a proton from this internal hydronium ion to acetate, when acetate is substituted at a chloride-binding site. Taken together, the results show that the mechanism of PSII proton transfer at pH 7.5 involves proton hopping through an internal, water-containing network.

Authors

No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, U.S. Gov't, Non-P.H.S.
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

31099580

Citation

Brahmachari, Udita, et al. "Water Bridges Conduct Sequential Proton Transfer in Photosynthetic Oxygen Evolution." The Journal of Physical Chemistry. B, vol. 123, no. 21, 2019, pp. 4487-4496.
Brahmachari U, Gonthier JF, Sherrill CD, et al. Water Bridges Conduct Sequential Proton Transfer in Photosynthetic Oxygen Evolution. J Phys Chem B. 2019;123(21):4487-4496.
Brahmachari, U., Gonthier, J. F., Sherrill, C. D., & Barry, B. A. (2019). Water Bridges Conduct Sequential Proton Transfer in Photosynthetic Oxygen Evolution. The Journal of Physical Chemistry. B, 123(21), 4487-4496. https://doi.org/10.1021/acs.jpcb.9b01523
Brahmachari U, et al. Water Bridges Conduct Sequential Proton Transfer in Photosynthetic Oxygen Evolution. J Phys Chem B. 2019 05 30;123(21):4487-4496. PubMed PMID: 31099580.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Water Bridges Conduct Sequential Proton Transfer in Photosynthetic Oxygen Evolution. AU - Brahmachari,Udita, AU - Gonthier,Jérôme F, AU - Sherrill,C David, AU - Barry,Bridgette A, Y1 - 2019/05/17/ PY - 2019/5/18/pubmed PY - 2019/5/18/medline PY - 2019/5/18/entrez SP - 4487 EP - 4496 JF - The journal of physical chemistry. B JO - J Phys Chem B VL - 123 IS - 21 N2 - Proton transfer using water bridges has been observed in bulk water, acid-base reactions, and several proton-translocating biological systems. In the photosynthetic water-oxidizing enzyme, photosystem II (PSII), protons from substrate water are transferred 35 Å from the Mn4CaO5 catalytic site to the chloroplast lumen. This process leads to acidification of the lumen and ATP synthesis. Water oxidation occurs in a flash-induced, five-step S n state cycle; acetate is a chloride-dependent inhibitor of the S2 to S3 step of this cycle. Here, we study the effect of acetate on a previous step of the cycle, the S1 to S2 transition, using reaction-induced infrared spectroscopy. PSII was isolated from spinach, and experiments were conducted at pH 7.5, using 532 nm laser flashes to advance the cycle from the dark-adapted state S1 to the S2 state. Isotope-editing of acetate reveals direct contributions to the S2-minus-S1 infrared spectrum consistent with protonation of bound acetate in PSII. In the acetate-derived S2-minus-S1 PSII spectra, an accompanying decrease in the intensity of a 2830 cm-1 band is observed when compared to the chloride control. The 2830 cm-1 band has been assigned previously to a stretching vibration of an internal, hydrated hydronium ion, W n+. Density functional studies of a catalytic site model predict the spontaneous transfer of a proton from this internal hydronium ion to acetate, when acetate is substituted at a chloride-binding site. Taken together, the results show that the mechanism of PSII proton transfer at pH 7.5 involves proton hopping through an internal, water-containing network. SN - 1520-5207 UR - https://www.unboundmedicine.com/medline/citation/31099580/Water_Bridges_Conduct_Sequential_Proton_Transfer_in_Photosynthetic_Oxygen_Evolution L2 - https://dx.doi.org/10.1021/acs.jpcb.9b01523 DB - PRIME DP - Unbound Medicine ER -
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