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Published June 2003 | public
Journal Article

^(15)N-^1H Residual Dipolar Coupling Analysis of Native and Alkaline-K79A Saccharomyces cerevisiae Cytochrome c

Abstract

Residual dipolar couplings (RDCs) and pseudocontact shifts are experimentally accessible properties in nuclear magnetic resonance that are related to structural parameters and to the magnetic susceptibility anisotropy. We have determined RDCs due to field-induced orientation of oxidized-K79A and reduced cytochrome c at pH 7.0 and oxidized-K79A cytochrome c at pH 11.1 through measurements of amide ^(15)N-^1H ^1J couplings at 800 and 500 MHz. The pH 7.0 RDCs for Fe(III)- and Fe(II)-cytochrome c together with available nuclear Overhauser effects were used to recalculate solution structures that were consistent with both sets of constraints. Molecular magnetic susceptibility anisotropy values were calculated for both redox states of the protein. By subtracting the residual dipolar couplings (RDCs) of the reduced form from those of the oxidized form measured at the same magnetic field (800 MHz), we found the RDC contribution of the paramagnetic metal ion in the oxidized protein. The magnetic susceptibility anisotropy, which was calculated from the structure, was found to be the same as that of the paramagnetic metal ion obtained independently from pseudocontact shifts, thereby indicating that the elements of secondary structure either are rigid or display the same mobility in both oxidation states. The residual dipolar coupling values of the alkaline-K79A form are small with respect to those of oxidized native cytochrome, whereas the pseudocontact shifts are essentially of the same magnitude, indicating local mobility. Importantly, this is the first time that mobility has been found through comparison of RDCs with pseudocontact shifts.

Additional Information

© 2003 The Biophysical Society. Published by Elsevier Inc. Received 27 September 2002, Accepted 21 January 2003. We thank Federico Rosell for providing samples of K79A cytochrome c. We acknowledge support from the Ministero dell'Istruzione, dell'Università e della Ricerca, Cofinanziamento 2001 MIUR COFIN2001) and European Community Network (grant FMRX-CT98-0218 to I.B.); Italian Consiglio Nazionale delle Richerche (Progetto Finalizzato Biotecnologie grant 01.00359.PF49 to P.T.); operating grant MT-14021 from the Canadian Institutes of Health Research and a Canada Research Chair (to A.G.M.); United States National Institutes of Health grant DK19038 (to H.B.G.); and Department of Energy grant DE-FG03-02ER15359 (to J.R.W.).

Additional details

Created:
August 19, 2023
Modified:
October 25, 2023