Hydroxylation and lyase reactions of steroids catalyzed by mouse cytochrome P450 17A1 (Cyp17a1)

Patterns of alteration in boar semen quality from 9 to 37 months old and improvement by protocatechuic acid

BACKGROUND

Comprehending the patterns of alteration in boar semen quality and identifying effective nutritional interventions are crucial for enhancing the productivity of commercial pig systems. This study aimed to examine the alteration in semen quality in boars, and assess the impact of protocatechuic acid (PCA) on semen quality during the phase of declining semen quality.

METHODS

In Exp. 1, a total of 38 Pig Improvement Company (PIC) boars were selected and their semen quality data were recorded from the age of 9 to 37 months. In Exp. 2, 18 PIC boars (28 months old) were randomly assigned into three groups (n = 6) and fed a basal diet, a basal diet containing 500 or 1,000 mg/kg PCA, respectively. The experiment lasted for 12 weeks.

RESULTS

The semen volume, concentration, and total number of spermatozoa in boars exhibited an increase from 9 to 19 months old and showed a significant linear decreased trend in 28, 24, and 22 months old. Sperm motility displayed an upward trajectory, reaching its peak at 20 months of age, and showed a significant linear decreased trend at 20 months old. Dietary supplementation of PCA demonstrated an effect to mitigate the decrease in semen volume, concentration of spermatozoa, total number of spermatozoa (P > 0.05), and significantly increased the sperm motility (P < 0.05). Moreover, supplementation of 1,000 mg/kg PCA significantly increased the sperm viability (P < 0.05). Analysis on cellular signaling pathways revealed that PCA restored serum testosterone levels and alleviated oxidative damage by upregulating the expression of HO-1, SOD2, and NQO1 in testicular stromal cells. Notably, PCA can enhance phosphorylation by selectively binding to AMP-activated protein kinase (AMPK) protein, thereby improving sperm mitochondrial function and augmenting sperm motility via PGC-1/Nrf1.

CONCLUSIONS

These data elucidated the pattern of semen quality variation in boars within the age range of 9 to 37 months old, and PCA has the potential to be a natural antioxidant to enhance sperm quality through modulation of the AMPK/PGC-1/Nrf1 signaling pathway.

Catalytic enhancements in cytochrome P450 2C19 by cytochrome b5

Human cytochrome P450 2C19 catalyzes P450 enzyme reactions of various substrates, including steroids and clinical drugs. Recombinant P450 2C19 enzyme with histidine tag was successfully expressed in Escherichia coli and purified using affinity column chromatography. Ultra-performance liquid chromatography-tandem mass (UPLC-MS/MS) spectrometry showed that the purified P450 2C19 enzyme catalyzed 5-hydroxylation reaction of omeprazole. The purified enzyme displayed typical type I binding spectra to progesterone with a Kd value of 4.5 ± 0.2 µM, indicating a tight substrate binding. P450 2C19 catalyzed the hydroxylation of progesterone to produce 21-hydroxy (OH) as a major and 17-OH product as a minor product. Steady-state kinetic analysis of progesterone 21-hydroxylation indicated that the addition of cytochrome b5 stimulated a five-times catalytic turnover number of P450 2C19 with a kcat value of 1.07 ± 0.08 min-1. The molecular docking model of progesterone in the active site of P450 2C19 displayed that the 21-carbon of progesterone was located close to the heme with a distance of 4.7 Å, suggesting 21-hydroxylation of progesterone is the optimal reaction of P450 2C19 enzyme for a productive orientation of the substrate. Our findings will help investigate the extent to which cytochrome b5 affects the metabolism of P450 2C19 to drugs and steroids.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-023-00219-8.

Proteomics, modeling, and fluorescence assays delineate cytochrome b5 residues involved in binding and stimulation of cytochrome P450 17A1 17,20-lyase

Cytochrome b5 (b5) is known to stimulate some catalytic activities of cytochrome P450 (P450, CYP) enzymes, although mechanisms still need to be defined. The reactions most strongly enhanced by b5 are the 17,20-lyase reactions of P450 17A1 involved in steroid biosynthesis. We had previously used a fluorescently labeled human b5 variant (Alexa 488-T70C-b5) to characterize human P450 17A1-b5 interactions, but subsequent proteomic analyses indicated that lysines in b5 were also modified with Alexa 488 maleimide in addition to Cys-70, due to disulfide dimerization of the T70C mutant. A series of b5 variants were constructed with Cys replacements for the identified lysine residues and labeled with the dye. Fluorescence attenuation and the function of b5 in the steroid lyase reaction depended on the modified position. Apo-b5 (devoid of heme group) studies revealed the lack of involvement of the b5 heme in the fluorescence attenuation. A structural model of b5 with P450 17A1 was predicted using AlphaFold-Multimer algorithms/Rosetta docking, based upon the individual structures, which predicted several new contacts not previously reported, that is, interactions of b5 Glu-48:17A1 Arg-347, b5 Glu-49:17A1 Arg-449, b5 Asp-65:17A1 Arg-126, b5 Asp-65:17A1 Arg-125, and b5 Glu-61:17A1 Lys-91. Fluorescence polarization assays with two modified b5 variants yielded Kd values (for b5-P450 17A1) of 120 to 380 nM, the best estimate of binding affinity. We conclude that both monomeric and dimeric b5 can bind to P450 17A1 and stimulate activity. Results with the mutants indicate that several Lys residues in b5 are sensitive to the interaction with P450 17A1, including Lys-88 and Lys-91.

Functional Characterization of Allelic Variations of Human Cytochrome P450 2C8 (V181I, I244V, I331T, and L361F)

The human cytochrome P450 2C8 is responsible for the metabolism of various clinical drugs as well as endogenous fatty acids. Allelic variations can significantly influence the metabolic outcomes. In this study, we characterize the functional effects of four nonsynonymous single nucleotide polymorphisms *15, *16, *17, and *18 alleles recently identified in cytochrome P450 2C8. The recombinant allelic variant enzymes V181I, I244V, I331T, and L361F were successfully expressed in Escherichia coli and purified. The steady-state kinetic analysis of paclitaxel 6-hydroxylation revealed a significant reduction in the catalytic activities of the V181I, I244V, and L361F variants. The calculated catalytic efficiency (k_cat/K_m) of these variants was 5-26% of that of the wild-type enzyme. The reduced activities were due to both decreased k_cat values and increased K_m values of the variants. The epoxidation of arachidonic acid by the variants was analyzed. The L361F variant only exhibited 4-6% of the wild-type catalytic efficiency in ω-9- and ω-6-epoxidation reactions to produce 11,12-epoxyeicosatrienoic acid (EET) and 14,15-EET, respectively. These reductions were mainly due to a decrease in the k_cat value of the L361F variant. The binding titration analysis of paclitaxel and arachidonic acid showed that all variants had similar affinities to those of the wild-type (10-14 μM for paclitaxel and 20-49 μM for arachidonic acid). The constructed paclitaxel docking model of the variant enzyme suggests that the L361F substitution leads to the incorrect orientation of paclitaxel in the active site, with the 6'C of paclitaxel displaced from the productive catalytic location. This study suggests that individuals carrying the newly identified P450 2C8 allelic variations are likely to have an altered metabolism of clinical medicines and production of fatty acid-derived signal molecules.

Steroid 17α-hydroxylase/17, 20-lyase (cytochrome P450 17A1)

Cytochrome P450 (P450) 17A1 plays a key role in steroidogenesis, in that this enzyme catalyzes the 17α-hydroxylation of both pregnenolone and progesterone, followed by a lyase reaction to cleave the C-20 land C-21 carbons from each steroid. The reactions are important in the production of both glucocorticoids and androgens. The enzyme is critical in humans but is also a drug target in treatment of prostate cancer. Detailed methods are described for the heterologous expression of human P450 17A1 in bacteria, purification of the recombinant enzyme, reconstitution of the enzyme system in the presence of cytochrome b5, and chromatographic procedures for sensitive analyses of reaction products. Historic assay approaches are reviewed. Some information is also provided about outstanding questions in the research field, including catalytic mechanisms and searches for selective inhibitors.