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

Area of Science:

• Pharmacogenetics
• Enzyme kinetics
• Structural biology

Background:

• Cytochromes P450 (CYP) are crucial for drug metabolism, with genetic variations impacting drug efficacy.
• CYP2C9 is a key enzyme metabolizing numerous drugs, and its variants affect pharmacokinetics.
• The CYP2C9*8 allele, prevalent in African ancestry populations, is associated with altered drug metabolism.

Purpose of the Study:

• To elucidate the structural and binding characteristics of the CYP2C9*8 variant in complex with the drug losartan.
• To compare the binding of losartan to CYP2C9*8 versus wild-type (WT) CYP2C9 and the previously studied CYP2C9*3 variant.
• To understand the impact of the R150H amino acid substitution on enzyme activity and substrate interaction.

Main Methods:

• X-ray crystallography was used to determine the structure of the CYP2C9*8-losartan complex.
• Isothermal titration calorimetry (ITC) was employed to quantify the binding affinity of losartan to CYP2C9*8.
• Comparative analysis with existing structural and kinetic data for WT and CYP2C9*3 variants.

Main Results:

• The CYP2C9*8-losartan complex structure revealed similar overall conformation to WT but differed in losartan occupancy, with one molecule in the active site and another on the surface.
• Losartan was not observed in the access channel of the CYP2C9*8 complex, unlike in the WT complex.
• ITC studies indicated weaker binding of losartan to CYP2C9*8 compared to WT, though significantly stronger than the CYP2C9*3 variant.

Conclusions:

• The R150H substitution in CYP2C9*8 influences losartan binding site occupancy and affinity.
• CYP2C9*8 exhibits a distinct binding profile for losartan compared to WT and CYP2C9*3, highlighting substrate-dependent effects of genetic variations.
• These findings provide structural insights into drug-enzyme interactions and the impact of pharmacogenetic variations on drug metabolism.