Insights into the Genetic Variations of Human Cytochrome P450 2C9: Structural Analysis, Characterization and Comparison.

Sonia J Parikh,Manish B Shah,Sumit Kamat,Samuel P Boyson,Qinghai Zhang,Margaret Phillips,Thomas Yarbrough,Dylan Davie,Karen C Glass

doi:10.3390/ijms221910206

Abstract

Cytochromes P450 (CYP) are one of the major xenobiotic metabolizing enzymes with increasing importance in pharmacogenetics. The CYP2C9 enzyme is responsible for the metabolism of a wide range of clinical drugs. More than sixty genetic variations have been identified in CYP2C9 with many demonstrating reduced activity compared to the wild-type (WT) enzyme. The CYP2C9*8 allele is predominantly found in persons of African ancestry and results in altered clearance of several drug substrates of CYP2C9. The X-ray crystal structure of CYP2C9*8, which represents an amino acid variation from arginine to histidine at position 150 (R150H), was solved in complex with losartan. The overall conformation of the CYP2C9*8-losartan complex was similar to the previously solved complex with wild type (WT) protein, but it differs in the occupancy of losartan. One molecule of losartan was bound in the active site and another on the surface in an identical orientation to that observed in the WT complex. However, unlike the WT structure, the losartan in the access channel was not observed in the *8 complex. Furthermore, isothermal titration calorimetry studies illustrated weaker binding of losartan to *8 compared to WT. Interestingly, the CYP2C9*8 interaction with losartan was not as weak as the CYP2C9*3 variant, which showed up to three-fold weaker average dissociation constant compared to the WT. Taken together, the structural and solution characterization yields insights into the similarities and differences of losartan binding to CYP2C9 variants and provides a useful framework for probing the role of amino acid substitution and substrate dependent activity.

Highlights

Introduction published maps and institutional affilHuman cytochrome P450 (CYP) 2C9, a member of the CYP2C subfamily of Cytochromes P450 (CYP) enzymes, is an important drug metabolizing enzyme and represents as much as ~20%of the total hepatic cytochrome P450 content [1,2,3]
The goal of the current study is to further our understanding of how genetic variations in CYP2C9, located away from the active site, affect drug binding and metabolism in the active site
The results demonstrated similarities and differences in the CYP2C9 structure and function upon binding to losartan and provide valuable knowledge that would help infer the effect of single nucleotide polymorphisms on the metabolism of a commonly prescribed medication

Summary

Introduction

Of the total hepatic cytochrome P450 content [1,2,3]. It is predominantly responsible for the biotransformation of many prescribed clinical drugs that include anti-coagulant (S)warfarin, anti-hypertensive losartan, anti-convulsant phenytoin, anti-diabetics tolbutamide and glimepiride, as well as the commonly used analgesic ibuprofen [4,5,6,7]. CYP2C9 is a highly polymorphic enzyme that includes over 60 classified genetic variants, with at least 20 reported to possess altered activity [8,9]. The two most characterized and commonly found variant alleles include CYP2C9*2 and CYP2C9*3, and both are associated with reduced enzyme function and altered drug metabolism [10,11]. The less characterized variants that include CYP2C9*5, *6, *8, and *11 are found with high frequency in populations of African origin, and they are more common than *2 and *3 alleles in these iations.

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Results