AN NMR-DERIVED MODEL FOR THE SOLUTION STRUCTURE OF OXIDIZED THERMOTOGA-MARITIMA 1[FE-4-S-4] FERREDOXIN

The solution structure of the 60-residue 1[Fe-4-S-4] ferredoxin from t he hyperthermophilic bacterium Thermotoga maritima was determined base d on 683 distance and 35 dihedral angle restraints that were obtained from NMR data. In addition, data known from crystallographic studies o f ferredoxins was used for modeling of the iron-sulfur cluster and its environment. The protein shows a globular fold very similar to the fo ld of the related 1[Fe-4-S-4] ferredoxins from Desulfovibrio gigas and Desulfovibrio africanus, and elements of regular secondary structure similar to those in other ferredoxins were found in the T. maritima pr otein. In particular, the T. maritima protein displayed a beta-sheet s tructure made up of strands located at the very NH2 and COOH termini o f the protein, and an internal alpha-helix. The internal beta-sheet ob served in the D. gigas and D. africanus ferredoxins could not be confi rmed in T. maritima ferredoxin and is thus suggested to be only weakly present or even absent in this protein. This result suggests that the rmostability in ferredoxins is not necessarily correlated with the con tent of stable elements of regular secondary structure.