Ligand Environment of the S₂State of Photosystem II: A Study of the Hyperfine Interactions of the Tetranuclear Manganese Cluster by 2D¹⁴N HYSCORE Spectroscopy

Abstract

The solar water-splitting protein complex, photosystem II, catalyzes the light-driven oxidation of water to dioxygen in Nature. The four-electron oxidation reaction of water occurs at the tetranuclear manganese-calcium-oxo catalytic cluster that is present in the oxygen-evolving complex of photosystem II. The mechanism of light-driven water oxidation has been a subject of intense interest, and the oxygen-evolving complex of photosystem II has been studied extensively by structural and biochemical methods. While the recent X-ray crystal structures and single-crystal EXAFS investigations provide a model for the geometry of the tetranuclear manganese-calcium-oxo catalytic cluster, there is limited knowledge of the protein environment that surrounds the catalytic cluster. In this study, we demonstrate the application of two-dimensional hyperfine sublevel correlation spectroscopy to determine the magnetic couplings of the catalytic cluster with the (14)N atoms of surrounding amino acid residues in the S(2) state of the oxygen-evolving complex of photosystem II. We utilize two-dimensional difference spectroscopy to facilitate unambiguous assignments of the spectral features and identify at least three separate (14)N atoms that are interacting with the catalytic cluster in the S(2) state. The results presented here, for the first time, identify previously unknown ligands to the catalytic cluster of photosystem II and provide avenues for the assignment of residues by site-directed mutagenesis and the refinement of computational and mechanistic models of photosystem II.

Molecular mechanisms for generating transmembrane proton gradients

“…Comparing this structure with the S 2 model [262] predicts that the dangler Mn is oxidized forming S 2 and one of the waters attached to this Mn looses a proton to become a hydroxyl. This assignment for the Mn oxidation agrees with recent HYSCORE experiments [264]. Consistent with the S 1 structure, all of the bridging oxygens are deprotonated.…”

Ligation of D1-His332 and D1-Asp170 to the Manganese Cluster of Photosystem II from Synechocystis Assessed by Multifrequency Pulse EPR Spectroscopy

“…PCC 6803 found that the 4.8 MHz peak decreased or disappeared upon this mutation (see Figure S1). (40) A similar feature has now been observed in X -band ESEEM spectra of PSII isolated from higher plants (spinach(40–42) and pea seedlings(43)) as well as mesophilic(38,40) and thermophilic cyanobacteria. (36) Unfortunately, rather little information as to the strength of the magnetic interaction between this histidine nitrogen and the OEC can be derived from just one peak.…”

HYSCORE and DFT Studies of Proton-Coupled Electron Transfer in a Bioinspired Artificial Photosynthetic Reaction Center

“…In the present study, we use two-dimensional (2D) hyperfine sublevel correlation (HYSCORE) spectroscopy (see Transparent Methods) to obtain a quantitative measure of the hyperfine and quadrupolar parameters of the BiP-PF 10 ,+ radical (Chatterjee et al, 2013(Chatterjee et al, , 2012Coates et al, 2015;Dikanov et al, 2019Dikanov et al, , 2000Dikanov and Taguchi, 2018;Hö fer et al, 1986;Milikisiyants et al, 2011Milikisiyants et al, , 2010. 2D HYSCORE spectroscopy is similar to the pulsed EPR spectroscopy methods, electron nuclear double resonance (ENDOR), and electron spin echo envelope modulation (ESEEM) (Britt, 2003;Deligiannakis et al, 2000;Harmer et al, 2009;Lakshmi and Brudvig, 2001;Prisner et al, 2001), that are used for the study of electron-nuclear hyperfine interactions in paramagnetic systems.…”