Crystal structure of the human cytochrome P450 2C9*8 genetic variant
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Issue Date
2020-07
Authors
Kamat, Sumit S. '20
Degree
MS in Pharmaceutical Sciences
Advisor
Shah, Manish B
Committee Members
Dearborn, Richard E.
Glass, Karen C.
Glass, Karen C.
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Abstract
Cytochrome P450 (CYP) enzymes are one of the major xenobiotic metabolizing enzymes with increasing importance in pharmacogenetics. The human CYP2C9 enzyme that metabolizes over 15% of clinical drugs including warfarin, losartan, tolbutamide, etc. is highly polymorphic with more than eighty genetic variations identified thus far. Many of these variants have demonstrated significantly reduced activity compared with the wild-type (WT) enzyme. The CYP2C9*8 allele, prevalent among different populations and predominantly found in African-Americans with a frequency of around 0.06, is associated with altered clearance of several drug substrates of CYP2C9. The *8 represents an amino acid variation from arginine to histidine at position 150 (R150H). The R150H variant was generated using CYP2C9 WT construct by site-directed mutagenesis, and the enzyme was expressed in E. coli followed by protein purification and crystallization. The CYP2C9*8 was crystallized in the presence of the drug substrate losartan and the structure was determined using X-ray crystallography at 2.3 \303\205 resolution. The R150H, found on the surface of the protein on D-helix that is distal from the active site, illustrates minimal effect on the overall conformation of the protein compared to the WT. Despite subtle changes in the structure itself, there were clear differences in the binding of losartan compared to the previously solved CYP2C9 WT complex. One molecule of losartan was bound in the active site and one on the surface, consistent to that observed in the WT complex. However, unlike the WT complex, the losartan in the access channel was not observed in the *8 complex. In addition, the losartan turn-over rates measured using enzymatic assays differed significantly, with the variant demonstrating marked reduction in activity than the WT enzyme. The results yield insight into the role of simultaneous binding of multiple substrate molecules that may suggest a possible role of cooperativity and altered hydroxylation profile of losartan with this variant. Further studies are warranted to determine the role of such distal variation.
Citation
Kamat SS. Crystal structure of the human cytochrome P450 2C9*8 genetic variant [thesis]. Ann Arbor (MI): Proquest LLC; 2020. 57 p.
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