Modification of MM force fields around heme-Fe in the CYP-ligand complex and ab initio FMO calculations for the complex.

Cytochrome P450 (CYP) enzymes play essential roles in the synthesis and metabolic activation of physiologically active substances. CYP has a prosthetic heme (iron protoporphyrin IX) in its active center, where Fe ion (heme-Fe) is deeply involved in enzymatic reactions of CYP. To precisely describe the structure and electronic states around heme-Fe, we modified the force fields (FFs) around heme-Fe in molecular mechanics (MM) simulations and conducted ab initio fragment molecular orbital (FMO) calculations for the CYP-ligand complex. To describe the coordination bond between heme-Fe and its coordinated ligand (ketoconazole), we added FF between heme-Fe and the N atom of ketoconazole, and then the structure of the complex was optimized using the modified FF. Its adequacy was confirmed by comparing the MM-optimized structure with the X-ray crystal one of the CYP-ketoconazole complex. We also performed 100 ns molecular dynamics simulations and revealed that the coordination bonds around heme-Fe were maintained even at 310 K and that the CYP-ketoconazole structure was kept similar to the X-ray structure. Furthermore, we investigated the electronic states of the complex using the ab initio FMO method to identify the CYP residues and parts of ketoconazole that contribute to strong binding between CYP and ketoconazole. The present procedure of constructing FF between heme-Fe and ketoconazole can be applicable to other CYP-ligand complexes, and the modified FF can provide their accurate structures useful for predicting the specific interactions between CYP and its ligands.