Determining the Electronic Structure of Paramagnetic Intermediates in membrane proteins: A high-resolution 2D 1H hyperfine sublevel correlation study of the redox-active tyrosines of photosystem II

Electronic Structure of Tyrosyl D Radical of Photosystem II, as Revealed by 2D-Hyperfine Sublevel Correlation Spectroscopy

“…Using the values of spin densities listed in Table1, we estimate ρ C 4 +O = 0.26, and assuming ρ C 4 = 0, we finally obtain r = 1.73 ± 0.03 Å. Similar distance was calculated for Mn-depleted PS II from spinach using ENDOR (1.67 Å, [58]), while longer distances for the PS II from T. elongatus (1.84 Å, [59]) and Synechocystis (1.87-1.9 Å, [36,58]). No indication for a second H-bond was found, which is in line with earlier reports [36,58,59].…”

“…Therefore, hyperfine coupling values of β protons are enzyme-and species-dependent. Previous studies [35,36,57] showed that one of the two methylene protons (β 2 ) is closer to the phenolic ring plane and thus has considerably smaller a 2 compared to that of β 1 . The large isotropic coupling constant a 1 = 27.9 MHz obtained for the H#1 peak is in line with the typical values 23-30 MHz assigned to β 1 proton.…”

“…TyrD radical has been studied by using HYSCORE in a variety of organisms: in spinach [33], in the green alga Chlamydomonas reinhardtii [57] and in the cyanobacterium Synechocystis [36], but only in Mn depleted PS II. It should be noted that in the previous studies one τ value was used and there are blind spots at the position of the A y coupling of the rhombic proton limiting the ability to determine this component accurately.…”

“…In most cases, the continuous wave Electron Paramagnetic Resonance (cw-EPR) technique fails to describe in detail these couplings, owing to the spectral broadening from magnetic interactions of different origin. Instead, pulsed EPR spectroscopic techniques, including Electron-Spin Echo Envelope Modulation (ESEEM), Electron-Nuclear Double Resonance (ENDOR), 2-Dimensional Hyperfine Sublevel Correlation Spectroscopy (2D-HYSCORE) are useful tools for the study of these interactions and have been extensively used to characterize the hyperfine couplings of tyrosyl radicals [33][34][35][36][37][38][39]. In the case of cyanobacterial PSII, the most detailed description of the structural environment of Y D…”

“…• , but solely in unfunctional Mn-depleted membranes [33,36]. It should be noted that even if the cyanobacterial and the higher plant PSII present similar structural and functional similarities [40], some spectroscopic differences have been reported [41][42][43][44].…”