NMR study of the structural characteristics of variants of yeast iso‐1‐cytochrome c in which unvaried aromatic residues have been substituted

Abstract

The structures of variants of yeast iso‐1‐cytochrome c, in which the previously unchanged Tyr48 and Tyr48 + Trp59 have been replaced by Phe, have been characterised by NMR. The NMR data indicated that the structures of the variant cytochromes c are very similar to the wild‐type protein. In particular, the heme environment and interactions of the heme macrocycle were shown to be preserved. The observation of chemical shift differences have allowed for the assessment of conformational changes. The substitution of Trp59 by Phe may have caused a small conformational change, a manifestation of which is the observed chemical shift differences at His39, Val57 and Tyr74. The structural basis for the reduction in redox potential accompanying the amino acid substitutions is discussed and the proposal made that the changes in potential are a direct consequence of the side chain properties and do not result primarily from conformational changes.

Effects of the Tyr64 Substitution on the Stability of Cytochrome c553, a low Oxidoreduction‐Potential Cytochrome from Desulfovibrio vulgaris Hildenborough

“…This value is very small but may be the sum of several antagonist effects. Previous experiments performed on c-type cytochromes have shown that substitution of the invariant Tyr48 residue by a phenylalanine residue induces small conformational changes but that the oxidoreduction potential was found to be 22 mV lower (Thurgood et al, 1991). According to Kassner's hypothesis, the replacement of Tyr48 by phenylalanine in cytochrome c should lead to an increase in this value (Kassner, 1972).…”

Nuclear magnetic resonance of paramagnetic metalloproteins

“…482 NMR spectra of tuna, horse, and yeast iso-l-ferricytochromes c has been shown to give NOE connectivities to the phenyl ring protons and to the &CH2 protons of this residue. 300 These measurements have allowed the identification of the spin system of Phe 82 in the three cytochromes.…”