Substitution of Ca2+ and changes in the H-bond network near the oxygen-evolving complex of photosystem II. Issue 8 (14th February 2023)

• Record Type: Journal Article
• Authors: Mandal, Manoj; Saito, Keisuke; Ishikita, Hiroshi
• Is Part Of: Physical chemistry chemical physics. Volume 25:Issue 8(2023)
• Page Start: 6473
• Page End: 6480
• Publication Date: 2023-02-14
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/d2cp05036f
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Ca 2+, which is a prerequisite for oxygen evolution at the catalytic Mn4 CaO5 cluster in photosystem II, is replaced with other alkaline earth metals to investigate its influence on the H-bond network. Abstract : Ca 2+, which provides binding sites for ligand water molecules W3 and W4 in the Mn4 CaO5 cluster, is a prerequisite for O2 evolution in photosystem II (PSII). We report structural changes in the H-bond network and the catalytic cluster itself upon the replacement of Ca 2+ with other alkaline earth metals, using a quantum mechanical/molecular mechanical approach. The small radius of Mg 2+ makes W3 donate an H-bond to D1-Glu189 in Mg 2+ -PSII. If an additional water molecule binds at the large surface of Ba 2+, it donates H-bonds to D1-Glu189 and the ligand water molecule at the dangling Mn, altering the H-bond network. The potential energy profiles of the H-bond between D1-Tyr161 (TyrZ) and D1-His190 and the interconversion between the open- and closed-cubane S2 conformations remain substantially unaltered upon the replacement of Ca 2+ . Remarkably, the O5⋯Ca 2+ distance is shortest among all O5⋯metal distances irrespective of the radius being larger than that of Mg 2+ . Furthermore, Ca 2+ is the only alkaline earth metal that equalizes the O5⋯metal and O2⋯metal distances and facilitates the formation of the symmetric cubane structure.