Two-Dimensional HYSCORE Spectroscopy of Superoxidized Manganese Catalase: A Model for the Oxygen-Evolving Complex of Photosystem II

Abstract

The solar water-splitting protein complex, photosystem II (PSII), catalyzes one of the most energetically demanding reactions in Nature by using light energy to drive a catalyst capable of oxidizing water. The water oxidation reaction takes place at the tetra-nuclear manganese calcium-oxo (Mn4Ca-oxo) cluster at the heart of the oxygen-evolving complex (OEC) of PSII. Previous studies have determined the magnetic interactions between the paramagnetic Mn4Ca-oxo cluster and its environment in the S2 state of the OEC. The assignments for the electron-nuclear magnetic interactions that were observed in these studies were facilitated by the use of synthetic dimanganese di-μ-oxo complexes. However, there is an immense need to understand the effects of the protein environment on the coordination geometry of the Mn4Ca-oxo cluster in the OEC of PSII. In the present study, we use a proteinaceous model system to examine the protein ligands that are coordinated to the dimanganese catalytic center of manganese catalase from Lactobacillus plantarum. We utilize two-dimensional hyperfine sublevel correlation (2D HYSCORE) spectroscopy to detect the weak magnetic interactions of the paramagnetic dinuclear manganese catalytic center of superoxidized manganese catalase with the nitrogen and proton atoms of the surrounding protein environment. We obtain a complete set of hyperfine interaction parameters for the protons of a water molecule that is directly coordinated to the dinuclear manganese center. We also obtain a complete set of hyperfine and quadrupolar interaction parameters for two histidine ligands as well as a coordinated azide ligand, in azide-treated superoxidized manganese catalase. On the basis of the values of the hyperfine interaction parameters of the dimanganese model, manganese catalase, and those of the S2 state of the OEC of PSII, for the first time, we discuss the impact of a proteinaceous environment on the coordination geometry of multinuclear manganese clusters.

Manganese Oxidation State Assignment for Manganese Catalase

“…Table 4 shows that couplings close to these values are indeed calculated for the proximal proton of the histidine residue bound to the Mn(III) ion, i.e., His-181 in the A models and His-69 in model B. Based on our current assignment of the Mn(III) oxidation state to Mn 2 , we attribute this proton coupling as arising from the proximal proton on the His-181 residue and not the His-69 residue as assigned by Coates et al 12 In summary, comparison of BS-DFT calculated hfcs of the superoxidized state of manganese catalase with experimental results shows that the Mn 1 center is in the IV oxidation state with the Mn 2 center having the III oxidation state. These results are completely opposite to the interpretation suggested based solely on experimental results.…”

“…These are in general agreement with the experimentally observed values of −5.75 and −6.0 MHz experimentally assigned to a Mn(III) ligand nitrogen and 2.7 and 3.0 MHz assigned to a Mn(IV). 12,18 Model B is in direct agreement with the experimental assignments which assigned Mn1 as Mn(III), however model A and model A (OH) show equally good agreement and thus do not allow a distinction to be made between the different models.…”

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.…”

Comparison of Experimental and Broken Symmetry Density Functional Theory Calculated Electron Paramagnetic Resonance Parameters for the Manganese Catalase Active Site in the Superoxidized MnIII/MnIV State

“…In addition to the catalytically active oxidation states of (Mn II ) 2 and (Mn III ) 2 , a mixed valence state, Mn II Mn III , as well as a superoxidized Mn III Mn IV state, may also be formed via the addition of various oxidizing and reducing agents. − The superoxidized Mn III Mn IV state of MnCat has received significant attention as it displays an S = 1/2 ground state, making it amenable to study via electron paramagnetic resonance (EPR) techniques. − The EPR spectra of MnCat closely resembles the spectra seen when studying the oxygen evolving complex (OEC) in its S 2 state, which is in agreement with the di-μ-oxo glutamate motif together with further glutamate and histidine ligation observed in both structures. As a result of this, the superoxidized state has been studied using various experimental and theoretical techniques. − …”