Hydrogen-1 nuclear magnetic resonance investigation of Clostridium pasteurianum rubredoxin: previously unobserved signals.

ABSTRACT

Previously unobserved signals were located in the 470-MHz 1H NMR spectra of oxidized and reduced rubredoxin (Rd) from Clostridium pasteurianum. When the protein was oxidized, some of the resonances broadened beyond detection. Longitudinal relaxation (T1) measurements identified a number of these peaks as arising from residues close to the paramagnetic iron; these resonances exhibited short T1 values attributable to the dominant electron-nuclear dipolar relaxation mechanism. The chemical shifts of these peaks were not strongly dependent on the oxidation state of the protein, although relative ratios of line widths of several peaks in the spectra of oxidized and reduced Rd suggested localized conformational changes of the protein as a result of oxidation. Furthermore, spectra of the oxidized protein collected in the range 8-60 degrees C revealed no appreciable changes in the chemical shifts of these peaks with temperature. These results seem to point out a negligible dipolar contribution, due to either magnetic anisotropy or zero field splitting, to the observed shifts in the spectrum of oxidized Rd. Resonances were assigned to tyrosine-11 or phenylalanine-49 (but not to either specifically) on the basis of their T1 values and the X-ray diffraction data of the protein molecule [Watenpaugh, K. D., Sieker, L. C., Herriott, J. R., & Jensen, L. H. (1973) Acta Crystallogr., Sect. B Struct. Crystallogr. Cryst. Chem. B29, 943-956; and a further refinement deposited with the Protein Data Bank]. An upfield-shifted peak at about -1.1 ppm in the spectra of both oxidized and reduced Rd was assigned to a methyl group.(ABSTRACT TRUNCATED AT 250 WORDS)