3-DIMENSIONAL SOLUTION STRUCTURE OF THE CYANIDE ADDUCT OF A MET80ALA VARIANT OF SACCHAROMYCES-CEREVISIAE ISO-1-CYTOCHROME-C - IDENTIFICATION OF LIGAND-RESIDUE INTERACTIONS IN THE DISTAL HEME CAVITY

The H-1 NMR spectrum of the the cyanide adduct of a triply mutated Sac charomyces cerevisiae iso-1-cytochrome c (His39Gln/Met80Ala/Cys102Ser) in the oxidized form has been assigned through 1D NOE and 2D COSY, TO CSY, NOESY, and NOE-NOESY experiments; 562 protons out of a total of 6 83 have been assigned. The solution structure, the first of a paramagn etic heme protein, was determined using 1426 meaningful NOE constraint s out of a total of 1842 measured NOEs. The RMSD values at the stage o f restrained energy minimization of 17 structures obtained from distan ce geometry calculations are 0.68 +/- 0.11 and 1.32 +/- 0.14 Angstrom for the backbone and all heavy atoms, respectively. The quality, in te rms of RMSD, of the present structure is the same as that obtained for the solution structure of the diamagnetic horse heart ferrocytochrome c [Qi, P. X., et al. (1994) Biochemistry 33, 6408-6419]. The secondar y structure elements and the overall folding in the variant are observ ed to be the same as those of the wild-type protein for which the X-ra y structure is available. However, the replacement of the methionine a xial ligand with an alanine residue creates a ligand-binding ''distal cavity.'' The properties of the distal cavity seen in this solution st ructure are compared to those of other heme proteins.