SOLUTION STRUCTURE OF OXIDIZED CYTOCHROME C(6) FROM THE GREEN-ALGA MONORAPHIDIUM-BRAUNII

Cytochrome c(6) from Monoraphidium braunii, an 89-amino acid electron transfer protein, has been investigated by NMR in solution, in its oxi dized form, at pH 7 and 300 K. By using a combination of COSY, TOCSY, and NOESY experiments, 84% of the proton resonances have been assigned . A total of 1668 experimental NOE constraints, 1109 of which were mea ningful, together with 288 pseudocontact shifts, have been used to det ermine the structure in solution. This is represented as a family of 4 0 structures which have been energy minimized. The rmsd values with re spect to the mean structure are 0.57 +/- 0.08 and 0.94 +/- 0.09 Angstr om for the backbone and heavy atoms, respectively. The structure has b een found to be very similar to that of the reduced form, except for a rearrangement in propionate 7, a feature which has been observed in a ll c-type cytochromes investigated so far. Such a feature could be rel evant for the efficiency of the electron transfer pathway with either the oxidizing or the reducing partners. Other differences in the oxida tion states have been noted in the region proposed to be involved in t he interaction with the physiological partners.