Human Cytochrome CYP17A1: The Structural Basis for Compromised Lyase Activity with 17-Hydroxyprogesterone

Area of Science:

• Biochemistry
• Enzymology
• Molecular Biology

Background:

• Cytochrome P450 (CYP17A1) is essential for androgen biosynthesis, catalyzing 17-hydroxylation and C17-C20 lyase reactions.
• Prostate cancer progression is linked to androgens, driving interest in CYP17A1 inhibitors.
• Human CYP17A1 exhibits significantly lower C-C bond cleavage efficiency for 17-hydroxyprogesterone (17-OH PROG) compared to 17-hydroxypregnenolone (17-OH PREG).

Purpose of the Study:

• To elucidate the distinct reaction mechanisms of CYP17A1 with 17-OH PREG and 17-OH PROG.
• To provide a structural basis for the observed differences in lyase activity between these substrates.

Main Methods:

• Solvent isotope effect studies to probe reaction mechanisms.
• Cryoreduction and resonance Raman spectroscopy to trap and characterize reaction intermediates.
• Comparative analysis of CYP17A1 kinetics and intermediate structures for both substrates.

Main Results:

• Solvent isotope effects suggest a Compound I-mediated hydroxylase activity for PROG but exclude it from AD formation via the lyase reaction.
• Cryoreduction and Raman spectroscopy identified key hemiketal intermediates.
• CYP17A1 exhibits more facile protonation of the ferric peroxo-intermediate with 17-OH PROG than with 17-OH PREG, and distinct H-bonding interactions with the peroxo fragment.

Conclusions:

• The study provides definitive evidence for differential reaction pathways and intermediate stabilization based on the substrate.
• Structural differences, including H-bonding patterns and protonation ease, explain the significantly lower lyase activity of CYP17A1 with 17-OH PROG in humans.
• These findings offer crucial insights for the rational design of selective CYP17A1 inhibitors for prostate cancer therapy.