AN NMR-DERIVED MODEL FOR THE SOLUTION STRUCTURE OF OXIDIZED PUTIDAREDOXIN, A 2-FE, 2-S FERREDOXIN FROM PSEUDOMONAS

A model for the solution structure of oxidized putidaredoxin (Pdx), a 106-residue globular protein containing a Fe2S2 cluster, has been determined using homonuclear NMR methods. Pdx is the first of the class of Fe(2)S(2)Cys(4) ferredoxins which act as electron-transfer partners for P-450 monooxygenases to be structurally characterized, and no crystal structure has been determined for Pdx or for any closely homologous protein. Pdx is the physiological redox partner of cytochrome P-450(cam). A total of 878 NOE distance constraints, 66 phi angular constraints derived from NH-CalphaH coupling constants, and five paramagnetic broadening constraints were used in simulated annealing structural refinements to obtain a family of structures with pairwise rms deviations of 1.14 Angstrom for backbone atoms and 1.80 Angstrom for all nonhydrogen atoms. Paramagnetic broadening of resonances within a ca. 8-Angstrom radius of the metal duster prevents the use of NMR-derived constraints in this region of the protein; structural constraints used to model the environment of the metal cluster were obtained from site-directed mutagenesis and model compounds and by comparison with known ferredoxin structures. Pdx retains a similar folding topology to other structurally characterized Fe(2)S(2)Cys(4) ferredoxins but differs from the other ferredoxins in containing a significantly more compact structure in the C-terminal half of the protein.