Background:
There is a large inter-individual variation in cytochrome P450 2C19
(CYP2C19) activity. The variability can be caused by the genetic polymorphism of CYP2C19 gene.
This study aimed to investigate the molecular and kinetics basis for activity changes in three alleles
including CYP2C19*23, CYP2C19*24 and CYP2C19*25found in the Chinese population.
Methods:
The three variants expressed by bacteria were investigated using substrate (omeprazole and 3-
cyano-7-ethoxycoumarin[CEC]) and inhibitor (ketoconazole, fluoxetine, sertraline and loratadine)
probes in enzyme assays along with molecular docking.
Results:
All alleles exhibited very low enzyme activity and affinity towards omeprazole and CEC
(6.1% or less in intrinsic clearance). The inhibition studies with the four inhibitors, however, suggested
that mutations in different variants have a tendency to cause enhanced binding (reduced IC50 values).
The enhanced binding could partially be explained by the lower polar solvent accessible surface area of
the inhibitors relative to the substrates. Molecular docking indicated that G91R, R335Q and F448L, the
unique mutations in the alleles, have caused slight alteration in the substrate access channel morphology
and a more compact active site cavity hence affecting ligand access and binding. It is likely that these
structural alterations in CYP2C19 proteins have caused ligand-specific alteration in catalytic and inhibitory
specificities as observed in the in vitro assays.
Conclusion:
This study indicates that CYP2C19 variant selectivity for ligands was not solely governed
by mutation-induced modifications in the active site architecture, but the intrinsic properties of the
probe compounds also played a vital role.
Specificity and mechanism of carbohydrate demethylation by cytochrome P450 monooxygenases