Detection of the water-binding sites of the oxygen-evolving complex of Photosystem II using W-band 17O electron-electron double resonance-detected NMR spectroscopy.
Related Articles Detection of the water-binding sites of the oxygen-evolving complex of Photosystem II using W-band 17O electron-electron double resonance-detected NMR spectroscopy.
J Am Chem Soc. 2012 Oct 10;134(40):16619-34
Authors: Rapatskiy L, Cox N, Savitsky A, Ames WM, Sander J, Nowaczyk MM, Rögner M, Boussac A, Neese F, Messinger J, Lubitz W
Abstract
Water binding to the Mn(4)O(5)Ca cluster of the oxygen-evolving complex (OEC) of Photosystem II (PSII) poised in the S(2) state was studied via H(2)(17)O- and (2)H(2)O-labeling and high-field electron paramagnetic resonance (EPR) spectroscopy. Hyperfine couplings of coordinating (17)O (I = 5/2) nuclei were detected using W-band (94 GHz) electron-electron double resonance (ELDOR) detected NMR and Davies/Mims electron-nuclear double resonance (ENDOR) techniques. Universal (15)N (I = ½) labeling was employed to clearly discriminate the (17)O hyperfine couplings that overlap with (14)N (I = 1) signals from the D1-His332 ligand of the OEC (Stich Biochemistry 2011, 50 (34), 7390-7404). Three classes of (17)O nuclei were identified: (i) one ?-oxo bridge; (ii) a terminal Mn-OH/OH(2) ligand; and (iii) Mn/Ca-H(2)O ligand(s). These assignments are based on (17)O model complex data, on comparison to the recent 1.9 Å resolution PSII crystal structure (Umena Nature 2011, 473, 55-60), on NH(3) perturbation of the (17)O signal envelope and density functional
theory calculations. The relative orientation of the putative (17)O ?-oxo bridge hyperfine tensor to the (14)N((15)N) hyperfine tensor of the D1-His332 ligand suggests that the exchangeable ?-oxo bridge links the outer Mn to the Mn(3)O(3)Ca open-cuboidal unit (O4 and O5 in the Umena et al. structure). Comparison to literature data favors the Ca-linked O5 oxygen over the alternative assignment to O4. All (17)O signals were seen even after very short (