Tags

Type your tag names separated by a space and hit enter

Energetics of Ionized Water Molecules in the H-Bond Network near the Ca2+ and Cl- Binding Sites in Photosystem II.
Biochemistry. 2020 Jul 12 [Online ahead of print]B

Abstract

In photosystem II, water oxidation occurs at the oxygen-evolving complex (OEC). The presence of a hydronium ion (H3O+) was proposed at the Cl- binding site and Ca2+-depleted OEC. Using a quantum mechanical/molecular mechanical approach, we report the stability of H3O+ in the PSII protein environment. Neither release of the proton from ligand water molecule W2 at the OEC nor formation of H3O+ at Cl- is energetically favorable. In contrast, H3O+ can exist at the Ca2+-depleted OEC. Even when H3O+ exists in Ca2+-depleted PSII, the H-bond network of the redox-active tyrosine (TyrZ) remains unaltered, retaining the unusually short low-barrier H-bond with D1-His190, and the redox potential of TyrZ, Em(TyrZ), remains unaltered. These observations explain why the oxidation of the Ca2+-depleted Mn4O5 cluster by TyrZ (i.e., the S2 to S3 transition) is not inhibited at low pH. It seems likely that Ca2+ plays a role in not only (i) maintaining the H-bond network and facilitating TyrZ oxidation [tuning Em(TyrZ)] but also (ii) providing the valence of +2, decreasing the pKa of the ligand molecule (W1), and facilitating the release of the proton from W1 in the S2 to S3 transition together with Cl-.

Authors+Show Affiliations

Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan. Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan.Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan.Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan. Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan.

Pub Type(s)

Journal Article

Language

eng

PubMed ID

32603092

Citation

Saito, Keisuke, et al. "Energetics of Ionized Water Molecules in the H-Bond Network Near the Ca2+ and Cl- Binding Sites in Photosystem II." Biochemistry, 2020.
Saito K, Mandal M, Ishikita H. Energetics of Ionized Water Molecules in the H-Bond Network near the Ca2+ and Cl- Binding Sites in Photosystem II. Biochemistry. 2020.
Saito, K., Mandal, M., & Ishikita, H. (2020). Energetics of Ionized Water Molecules in the H-Bond Network near the Ca2+ and Cl- Binding Sites in Photosystem II. Biochemistry. https://doi.org/10.1021/acs.biochem.0c00177
Saito K, Mandal M, Ishikita H. Energetics of Ionized Water Molecules in the H-Bond Network Near the Ca2+ and Cl- Binding Sites in Photosystem II. Biochemistry. 2020 Jul 12; PubMed PMID: 32603092.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Energetics of Ionized Water Molecules in the H-Bond Network near the Ca2+ and Cl- Binding Sites in Photosystem II. AU - Saito,Keisuke, AU - Mandal,Manoj, AU - Ishikita,Hiroshi, Y1 - 2020/07/12/ PY - 2020/7/1/pubmed PY - 2020/7/1/medline PY - 2020/7/1/entrez JF - Biochemistry JO - Biochemistry N2 - In photosystem II, water oxidation occurs at the oxygen-evolving complex (OEC). The presence of a hydronium ion (H3O+) was proposed at the Cl- binding site and Ca2+-depleted OEC. Using a quantum mechanical/molecular mechanical approach, we report the stability of H3O+ in the PSII protein environment. Neither release of the proton from ligand water molecule W2 at the OEC nor formation of H3O+ at Cl- is energetically favorable. In contrast, H3O+ can exist at the Ca2+-depleted OEC. Even when H3O+ exists in Ca2+-depleted PSII, the H-bond network of the redox-active tyrosine (TyrZ) remains unaltered, retaining the unusually short low-barrier H-bond with D1-His190, and the redox potential of TyrZ, Em(TyrZ), remains unaltered. These observations explain why the oxidation of the Ca2+-depleted Mn4O5 cluster by TyrZ (i.e., the S2 to S3 transition) is not inhibited at low pH. It seems likely that Ca2+ plays a role in not only (i) maintaining the H-bond network and facilitating TyrZ oxidation [tuning Em(TyrZ)] but also (ii) providing the valence of +2, decreasing the pKa of the ligand molecule (W1), and facilitating the release of the proton from W1 in the S2 to S3 transition together with Cl-. SN - 1520-4995 UR - https://www.unboundmedicine.com/medline/citation/32603092/Energetics_of_ionized_water_molecules_in_the_H-bond_network_near_the_Ca2+_and_Cl-_binding_sites_in_photosystem_II L2 - https://doi.org/10.1021/acs.biochem.0c00177 DB - PRIME DP - Unbound Medicine ER -
Try the Free App:
Prime PubMed app for iOS iPhone iPad
Prime PubMed app for Android
Prime PubMed is provided
free to individuals by:
Unbound Medicine.