An additional electrostatic interaction between adrenodoxin and P450c27 (CYP27A1) results in tighter binding than between adrenodoxin and P450scc (CYP11A1)

Mitochondrial cytochrome P450c27 (product of the CYP27A1 gene) is found to have significantly higher affinity for the common redox partner adrenodoxin than another mitochondrial P450, P450scc (product of the CYP11A1 gene). To investigate the basis of the similar to 30-fold difference in adrenodoxin binding, two sets of P450c27 mutants were generated, expressed in Escherich ia coil, and purified. Mutations of one set were within the putative adreno doxin-binding site containing conserved lysine residues also crucial in P45 0scc for binding adrenodoxin, The second set included mutations within a se quence aligning with the "meander region" of P450BM-3 proposed to be a site of redox-partner interactions in P450s (Hasemann, C. A. Kurumbail, R. G., Boddupalli, S. S., Peterson, J. A. and Deisenhofer, J. (1995) Structure 3, 41-62), Mutation of the :P450c27 conserved lysines (K354A and K358A) led to a similar to 20-fold increase in apparent K-s for adrenodoxin, confirming that these two positively charged residues conserved in mitochondrial P450s are important for adrenodoxin binding. Mutation of Arg-418, conserved in t he CYP27A1 family, to serine also decreased the affinity for adrenodoxin si milar to 20-fold. This residue is predicted to be located in the meander re gion. A triple K354A/K358A/R418S mutation profoundly reduced adrenodoxin bi nding. Thus, in contrast to P450scc, where mutation of the two conserved po sitively charged residues results in virtually complete inhibition of adren odoxin binding, in P450c27 there are three of such residues (Lys-354, Lys-3 58, and Arg-418) important for adrenodoxin interaction.