Faculty Collaboration Database

Human Cytochrome CYP17A1: The Structural Basis for Compromised Lyase Activity with 17-Hydroxyprogesterone. J Am Chem Soc 2018 Jun 13;140(23):7324-7331

Date

05/16/2018

Pubmed ID

29758981

Pubmed Central ID

PMC5999583

DOI

10.1021/jacs.8b03901

Scopus ID

2-s2.0-85047062533 (requires institutional sign-in at Scopus site)   33 Citations

Abstract

The multifunctional enzyme, cytochrome P450 (CYP17A1), plays a crucial role in the production of androgens, catalyzing two key reactions on pregnenolone (PREG) and progesterone (PROG), the first being a 17-hydroxylation to generate 17-OH PREG and 17-OH PROG, with roughly equal efficiencies. The second is a C-C bond scission or "lyase" reaction in which the C17-C20 bond is cleaved, leading to the eventual production of powerful androgens, whose involvement in the proliferation of prostate cancer has generated intense interest in developing inhibitors of CYP17A1. For humans, the significance of the C-C bond cleavage of 17-OH PROG is lessened, because it is about 50 times less efficient than for 17-OH PREG in terms of k_cat/K_m. Recognizing the need to clarify relevant reaction mechanisms involved with such transformations, we first report studies of solvent isotope effects, results of which are consistent with a Compound I mediated PROG hydroxylase activity, yet exclude this intermediate as a participant in the formation of androstenedione (AD) via the lyase reaction. This finding is also supported by a combination of cryoreduction and resonance Raman spectroscopy that traps and structurally characterizes the key hemiketal reaction intermediates. Adding to a previous study of PREG and 17-OH PREG metabolism, the current work provides definitive evidence for a more facile protonation of the initially formed ferric peroxo-intermediate for 17-OH PROG-bound CYP17A1, compared to the complex with 17-OH PREG. Importantly, Raman characterization also reveals an H-bonding interaction with the terminal oxygen of the peroxo fragment, rather than with the proximal oxygen, as is present for 17-OH PREG. These factors would favor a diminished lyase activity of the sample with 17-OH PROG relative to the complex with 17-OH PREG, thereby providing a convincing structural explanation for the dramatic differences in activity for these lyase substrates in humans.

Author List

Mak PJ, Duggal R, Denisov IG, Gregory MC, Sligar SG, Kincaid JR

Author

James Kincaid PhD Department Chair and Professor, Biophysical Chemistry in the Chemistry department at Marquette University

MESH terms used to index this publication - Major topics in bold

17-alpha-Hydroxyprogesterone
Carbon-Carbon Lyases
Catalytic Domain
Humans
Hydrogen Bonding
Hydroxylation
Kinetics
Multifunctional Enzymes
Oxidation-Reduction
Spectrum Analysis, Raman
Steroid 17-alpha-Hydroxylase