Abstract 14132: The Crystal Structures Of Human Cytochrome P450 2C9 Provide Insights Into The Effect Of Genetic Variation And The Binding Of Losartan

Abstract

The human cytochrome P450 2C9 (CYP2C9) enzyme metabolizes many of the currently available medications that include anti-coagulant warfarin, anti-hypertensive losartan, anti-diabetics tolbutamide and glimepiride. Genetic variations in CYP2C9 that include the common alleles *2 and *3 have resulted in reduced enzyme activity leading to altered metabolism of various drug substrates compared with the wild-type (WT). The CYP2C9*2 genetic variant represent an amino acid change from arginine to cysteine at position 144. The crystal structure of CYP2C9 WT and the *2 variant complexed with losartan were recently published. However, the structure of these enzymes in the absence of any ligand or losartan is not available. Thus, the aim was to determine the ligand free structure of these enzymes and assess the hypothesis that the drug binding orchestrates the conformational change and leads to reorientation of amino acid sidechains to interact with losartan in the active site. The data for the CYP2C9 WT and the CYP2C9*2 crystals in the absence of any ligands was collected remotely at the Stanford Synchrotron Radiation Light Source and the structures were solved using x-ray crystallography. The ligand-free structure of the *2 variant revealed markedly different conformation compared to the recently published structure in complex with losartan. The changes in the F, F’, G and G’ helices indicate an open conformation in the absence of losartan compared to the losartan complex. Whereas the ligand-free structure of the WT illustrated similarity in the overall conformation to the previously published structures with losartan bound. Comparison of the ligand free structure of the CYP2C9 WT or the *2 variant with the losartan bound structure identified the amino acid sidechains important for interaction with the drug in the active site. Furthermore, the structure of the *2 variant in the absence or presence of losartan provided a useful framework to investigate the effect of amino acid substitution that leads to altered binding of the drug. In conclusion, the structural characterization of the CYP2C9 WT and the *2 variant yield insights into the conformational changes that occur upon binding of losartan and help understand the effect of genetic polymorphisms on drug metabolism.