Rationalising the Geometric Variation between the A and B Monomers in the 1.9 Å Crystal Structure of Photosystem II

• Published in: Chemistry : a European journal Vol. 21; no. 18; pp. 6780 - 6792
• Main Authors: Petrie, Simon, Stranger, Robert, Pace, Ron J.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 27.04.2015; WILEY‐VCH Verlag
• Subjects: Arginine - chemistry; Calcium - chemistry; Crystallography, X-Ray; DFT; Histidine - chemistry; Hydrogen Bonding; manganese; Manganese - chemistry; Models, Molecular; Oxidation-Reduction; Oxygen - chemistry; photosynthesis; Photosystem II Protein Complex - chemistry; photosystem II; Tyrosine - chemistry; hydrogen bonding; photosystem II; DFT; photosynthesis; manganese
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201406419

Density functional theory calculations are reported on a set of models of the water‐oxidising complex (WOC) of photosystem II (PSII), exploring structural features revealed in the most recent (1.9 Å resolution) X‐ray crystallographic studies of PSII. Crucially, we find that the variation in the Mn–Mn distances seen between the A and B monomers of this crystal structure can be entirely accounted for, in the low oxidation state (LOS) paradigm, by consideration of the interplay between two hydrogen‐bonding interactions involving proximate amino acid residues with the oxo bridges of the WOC, that is, His337 with O3 (which leads to a general elongation in the Mn–Mn distances between Mn1, Mn2 and Mn3) and Arg357 with O2 (which results in a specific elongation of the Mn2Mn3 distance). Where does H belong? Subtle shifts in hydrogen bonding, involving the proximate residues His337 and Arg357 (see figure) with the oxo bridges of the water‐oxidising complex, explain the significant variation between monomers in the highest‐resolution crystal structure yet reported for photosystem II.