SEQUENTIAL NMR RESONANCE ASSIGNMENT AND SECONDARY STRUCTURE OF FERROCYTOCHROME-C553 FROM DESULFOVIBRIO-VULGARIS HILDENBOROUGH

Two-dimensional nuclear magnetic resonance spectroscopy was used to assign the proton resonances of ferrocytochrome c553 from Desulfovibrio vulgaris Hildenbourough at 37-degrees-C and pH = 5.9. Only a few side-chain protons were not identified because of degeneracy or overlap. The spin systems of the 79 amino acids were identified by DQF-COSY and HOHAHA spectra in H2O and D2O. Sequential assignments were obtained from NOESY connectivities between adjacent amide, C(alpha)H, and C(beta)H protons. From sequential NH(i) --> NH(i+1) and long-range C(alpha)H(i) --> NH(i+3) connectivities, four stretches of helices were identified (2-->8, 34-->46, 53-->59, 67-->77). Long-range NOE between residues in three different helices provide qualitative information on the tertiary structure, in agreement with the general folding pattern of cytochrome c. The heme protons, including the propionate groups, were assigned, and the identification of Met 57 as sixth heme ligand was established. The dynamical behavior of the ring protons of the six tyrosines was analyzed in detail in terms of steric hindrance. The NMR data for ferrocytochrome C553 are consistent with the X-ray structure for the homologous cytochrome from D. vulgaris Miyazaki. On the basis of the secondary structure element and of observed chemical shift due to the heme ring current, a structural alignment of eukaryotic and prokaryotic cytochromes c is proposed.