Photochemically induced dynamic nuclear polarization NMR on photosystem II: donor cofactor observed in entire plant

Geertje J Janssen,Jörg Matysik,A Alia,Huub J M De Groot,Johannes Neugebauer,Denis G Artiukhin,Pavlo Bielytskyi

doi:10.1038/s41598-018-36074-z

Geertje J Janssen, Jörg Matysik + Show 5 more

Open Access

https://doi.org/10.1038/s41598-018-36074-z

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Abstract

The solid-state photo-CIDNP (photochemically induced dynamic nuclear polarization) effect allows for increase of signal and sensitivity in magic-angle spinning (MAS) NMR experiments. The effect occurs in photosynthetic reaction centers (RC) proteins upon illumination and induction of cyclic electron transfer. Here we show that the strength of the effect allows for observation of the cofactors forming the spin-correlated radical pair (SCRP) in isolated proteins, in natural photosynthetic membranes as well as in entire plants. To this end, we measured entire selectively 13C isotope enriched duckweed plants (Spirodela oligorrhiza) directly in the MAS rotor. Comparison of 13C photo-CIDNP MAS NMR spectra of photosystem II (PS2) obtained from different levels of RC isolation, from entire plant to isolated RC complex, demonstrates the intactness of the photochemical machinery upon isolation. The SCRP in PS2 is structurally and functionally very similar in duckweed and spinach (Spinacia oleracea). The analysis of the photo-CIDNP MAS NMR spectra reveals a monomeric Chl a donor. There is an experimental evidence for matrix involvement, most likely due to the axial donor histidine, in the formation of the SCRP. Data do not suggest a chemical modification of C-131 carbonyl position of the donor cofactor.

Highlights

The photochemically induced dynamic nuclear polarization magic-angle spinning (MAS) NMR technique is a unique analytical tool to extract detailed information at the atomic level from photochemically active photosynthetic reaction centers (RCs) as well as from another protein undergoing light-induced electron transfer[1,2]
Further removal of the light-harvesting core antenna proteins CP43 and CP47 leads to the photosystem 2 (PS2) RC or D1D2 complex (Fig. 1b) comprising the D1 and D2 polypeptides in which the two branches of cofactors are symmetrically arranged (Fig. 1c)
Photo-CIDNP MAS NMR studies on plant PS2 have been restricted to experiments on isolated D1D2 RC preparations from spinach (Spinacia oleracea) due to the difficulty to incorporate selective isotope labels into plant RCs

Summary

Introduction

The photochemically induced dynamic nuclear polarization (photo-CIDNP) magic-angle spinning (MAS) NMR technique is a unique analytical tool to extract detailed information at the atomic level from photochemically active photosynthetic reaction centers (RCs) as well as from another protein undergoing light-induced electron transfer[1,2]. A possible explanation of the electron-spin density shift was suggested to be the presence of a local electrostatic field close to ring III, created for example by the protonation of the keto-group of ring V7 Since it appears that the electron-spin density on the oxidized donor is localized on the axial histidine, a tilting of the axial histidine towards pyrrole ring IV causing π-π overlap of both aromatic systems was proposed. Such electronic structures might allow for the remarkable increase in redox potential of PS2 in comparison to bacterial RCs

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