1H nuclear-magnetic-resonance investigation of oxidized Fe4S4 ferredoxin from Thermotoga maritima. Hyperfine-shifted resonances, sequence-specific assignments and secondary structure.

The oxidized Fe4S4 ferredoxin from the hyperthermophilic bacterium Thermotoga maritima has been investigated by one- and two-dimensional NMR in order to characterize its hyperfine-shifted resonances originating from the cysteinyl cluster ligands and to assign its resonances in the diamagnetic shift range. The chemical shift and relaxation time pattern of the hyperfine-shifted signals is very similar to other oxidized Fe4S4 ferredoxins. A tentative sequence-specific assignment of these resonances according to a general pattern of chemical shift of cysteine protons versus sequence position of cluster ligand is presented. Furthermore, sequence-specific assignments for 85% of the amino acid residues that were obtained without any guidance by known X-ray structures of ferredoxins are given. They reveal the formation of at least two elements of secondary structure by the polypeptide chain of T. maritima ferredoxin: an alpha-helix comprising residues C43-D49 and a double-stranded antiparallel beta-sheet consisting of the N- and C-terminal parts of the protein. This folding pattern is very similar to that of the crystallographically characterized ferredoxin from the mesophile Desulfovibrio gigas [Kissinger, C.R., Sieker, L.C., Adman E.T. & Jensen, L.H. (1991) J. Mol. Biol. 219, 693-715] and therefore suggesting different mechanisms of stabilization for T. maritima ferredoxin and the ferredoxin from the hyperthermophilic archaeon Pyrococcus furiosus that was recently investigated by NMR [Teng, Q., Zhou, Z.H., Smith, E.T., Busse, S. C., Howard, J.B., Adams M.W.W. & La Mar, G.N. (1994) Biochemistry 33, 6316-6326].