Functional Characterization of Pharmcogenetic Variants of Human Cytochrome P450 2C9 in Korean Populations

Human cytochrome P450 2C9 is a highly polymorphic enzyme that is required for drug and xenobiotic metabolism. Here, we studied eleven P450 2C9 genetic variants—including three novel variants F69S, L310V, and Q324X—that were clinically identified in Korean patients. P450 2C9 variant enzymes were expressed in Escherichia coli and their bicistronic membrane fractions were prepared The CO-binding spectra were obtained for nine enzyme variants, indicating P450 holoenzymes, but not for the M02 (L90P) variant. The M11 (Q324X) variant could not be expressed due to an early nonsense mutation. LC-MS/MS analysis was performed to measure the catalytic activities of the P450 2C9 variants, using diclofenac as a substrate. Steady-state kinetic analysis revealed that the catalytic efficiency of all nine P450 2C9 variants was lower than that of the wild type P450 2C9 enzyme. The M05 (R150L) and M06 (P279T) variants showed high k(cat) values; however, their K(m) values were also high. As the M01 (F69S), M03 (R124Q), M04 (R125H), M08 (I359L), M09 (I359T), and M10 (A477T) variants exhibited higher K(m) and lower k(cat) values than that of the wild type enzyme, their catalytic efficiency decreased by approximately 50-fold compared to the wild type enzyme. Furthermore, the novel variant M07 (L310V) showed lower k(cat) and K(m) values than the wild type enzyme, which resulted in its decreased (80%) catalytic efficiency. The X-ray crystal structure of P450 2C9 revealed the presence of mutations in the residues surrounding the substrate-binding cavity. Functional characterization of these genetic variants can help understand the pharmacogenetic outcomes.

Streptomyces Cytochrome P450 Enzymes and Their Roles in the Biosynthesis of Macrolide Therapeutic Agents

The study of the genus Streptomyces is of particular interest because it produces a wide array of clinically important bioactive molecules. The genomic sequencing of many Streptomyces species has revealed unusually large numbers of cytochrome P450 genes, which are involved in the biosynthesis of secondary metabolites. Many macrolide biosynthetic pathways are catalyzed by a series of enzymes in gene clusters including polyketide and non-ribosomal peptide synthesis. In general, Streptomyces P450 enzymes accelerate the final, post-polyketide synthesis steps to enhance the structural architecture of macrolide chemistry. In this review, we discuss the major Streptomyces P450 enzymes research focused on the biosynthetic processing of macrolide therapeutic agents, with an emphasis on their biochemical mechanisms and structural insights.