High-field NMR studies of oxidized blue copper proteins: The case of spinach plastocyanin

The 800-MHz H-1 NMR spectra of oxidized plastocyanin from spinach are here reported. All hyperfine-shifted signals have been assigned through saturation transfer with the reduced diamagnetic species. To detect the copper(II)-bound cysteine beta-CH2 signals, a technique has been applied which is based on irradiation of regions where such signals are expected but not detected, and the corresponding saturation transfer on the reduced species is observed. At the end, a full spectrum is reconstructed which permits, for the first time, the complete H-1 NMR signal assignment of an oxidized blue copper protein. These data are discussed in terms of the factors affecting the line width as related to the electronic and geometric structure of the metal center. A Karplus-type relationship is proposed between the contact shift of the Cys-84 beta-CH2 pf otons and the Cu-S-C-H beta dihedral angle.