A structure-based model for cytochrome P450(cam)-putidaredoxin interactions

Putidaredoxin (Pdx) is a Fe2S2 ferredoxin which acts as the physiological reductant of cytochrome P-450(cam) (CYP101). A model for the solution structure of oxidized Pdx has been determined using NMR methods (Pochapsky et al (1994) Biochemistry 33, 6424-6432). H-1-N-15 correlations and redox-dependent amide exchange rates have also been described (Lyons et al (1996) Protein Sci 5, 627-639). Data obtained from mutagenesis and kinetic measurements concerning the interactions of Pdx and CYP101 are summarized. A model for the structure of the homologous ferredoxin adrenodoxin (Adx) is also described, and data concerning Adx activity are discussed in relation to this structure. The structures of Pdx and CYP101 were used as starting points for molecular modeling and molecular dynamics simulations. Close approach between the metal centers of the two proteins and interaction between aromatic residues on the surfaces of the proteins are premised. The resulting complex exhibits three intermolecular salt bridges, five intermolecular hydrogen bonds and a 12 Angstrom distance between the metal centers. The first direct observations of interaction between Pdx and CYP101 (by two-dimensional NMR of N-15-labeled Pdx in solution with CYP101) are described. The results of the NMR experiments indicate that conformational gating of the electron transfer complex between CYP101 and Pdx may be important.