Dataset Information

Xenopus laevis CYP17 regulates androgen biosynthesis independent of the cofactor cytochrome b5.

ABSTRACT: The enzyme CYP17 primarily regulates androgen production by mediating four reactions: conversion of pregnenolone and progesterone to 17-hydroxypregnenolone and 17-hydroxyprogesterone, respectively (17alpha-hydroxylase activity), followed by conversion of the 17-hydroxylated steroids to dehydroepiandrosterone and androstenedione, respectively (17,20-lyase activity). Most mammalian CYP17 isoforms have high 17alpha-hydroxylase relative to 17,20-lyase activities and preferentially mediate one of the two 17,20-lyase reactions. In contrast, Xenopus laevis CYP17 potently regulates all four reactions in the frog ovary. CYP17 isoforms generally rely on the cofactor cytochrome b(5) for the 17,20-lyase reaction, suggesting that the high lyase activity of Xenopus CYP17 might be due to a lesser dependence on b(5). The kinetics of Xenopus CYP17 expressed in yeast microsomes were therefore examined in the absence and presence of Xenopus on human b(5). Xenopus CYP17 mediated both 17,20-lyase reactions in the absence of b(5), confirming that the activity did not require b(5). However, both Xenopus and human b(5) slightly enhanced Xenopus CYP17-mediated lyase activity, indicating that the enzyme was still at least partially responsive to b(5). Surprisingly, only the human b(5) cofactor enhanced human CYP17-mediated lyase activity, implying that the human enzyme had more specific cofactor requirements than Xenopus CYP17. Studies using human/Xenopus chimeric b(5) proteins revealed that human b(5) residues 16-41 were important for the specific regulation of the lyase activity of HuCYP17, possibly serving as an interacting domain with the enzyme. CYP17 may therefore have evolved from a general producer of sex steroids in lower vertebrates to a more tightly regulated producer of both sex steroids and glucocorticoids in mammals.

SUBMITTER: Yang WH

PROVIDER: S-EPMC1513634 | biostudies-literature | 2005 Mar

REPOSITORIES: biostudies-literature

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Xenopus laevis CYP17 regulates androgen biosynthesis independent of the cofactor cytochrome b5.

Yang Wei-Hsiung WH Hammes Stephen R SR

The Journal of biological chemistry 20050107 11

The enzyme CYP17 primarily regulates androgen production by mediating four reactions: conversion of pregnenolone and progesterone to 17-hydroxypregnenolone and 17-hydroxyprogesterone, respectively (17alpha-hydroxylase activity), followed by conversion of the 17-hydroxylated steroids to dehydroepiandrosterone and androstenedione, respectively (17,20-lyase activity). Most mammalian CYP17 isoforms have high 17alpha-hydroxylase relative to 17,20-lyase activities and preferentially mediate one of the ...[more]

PMID: 15640159

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Project description:Membrane cytochrome b5 reductase is a pleiotropic oxidoreductase that uses primarily soluble reduced nicotinamide adenine dinucleotide (NADH) as an electron donor to reduce multiple biological acceptors localized in cellular membranes. Some of the biological acceptors of the reductase and coupled redox proteins might eventually transfer electrons to oxygen to form reactive oxygen species. Additionally, an inefficient electron transfer to redox acceptors can lead to electron uncoupling and superoxide anion formation by the reductase. Many efforts have been made to characterize the involved catalytic domains in the electron transfer from the reduced flavoprotein to its electron acceptors, such as cytochrome b5, through a detailed description of the flavin and NADH-binding sites. This information might help to understand better the processes and modifications involved in reactive oxygen formation by the cytochrome b5 reductase. Nevertheless, more than half a century since this enzyme was first purified, the one-electron transfer process toward potential electron acceptors of the reductase is still only partially understood. New advances in computational analysis of protein structures allow predicting the intramolecular protein dynamics, identifying potential functional sites, or evaluating the effects of microenvironment changes in protein structure and dynamics. We applied this approach to characterize further the roles of amino acid domains within cytochrome b5 reductase structure, part of the catalytic domain, and several sensors and structural domains involved in the interactions with cytochrome b5 and other electron acceptors. The computational analysis results allowed us to rationalize some of the available spectroscopic data regarding ligand-induced conformational changes leading to an increase in the flavin adenine dinucleotide (FAD) solvent-exposed surface, which has been previously correlated with the formation of complexes with electron acceptors.

Project description:Cytochrome P450 17A1 (CYP17A1) is an important drug target for castration resistant prostate cancer. It is a bi-functional enzyme, catalyzing production of glucocorticoid precursors by hydroxylation of pregnene-nucleus, and androgen biosynthesis by a second CC lyase step, at the expense of glucocorticoid production. Cytochrome b5 (cyt b5) is known to be a key regulator of the androgen synthesis reaction in vivo, by a mechanism that is not well understood. Two hypotheses have been proposed for the mechanism by which cyt b5 increases androgen biosynthesis. Cyt b5 could act as an allosteric effector, binding to CYP17A1 and either changing its selective substrate affinity or altering the conformation of the P450 to increase the catalytic rate or decrease unproductive uncoupling channels. Alternatively, cyt b5 could act as a redox donor for supply of the second electron in the P450 cycle, reducing the oxyferrous complex to form the reactive peroxo-intermediate. To understand the mechanism of lyase enhancement by cyt b5, we generated a redox-inactive form of cyt b5, in which the heme is replaced with a Manganese-protoporphyrin IX (Mn-b5), and investigated enhancement of androgen producing lyase reaction by CYP17A1. Given the critical significance of a stable membrane anchor for all of the proteins involved and the need for controlled stoichiometric ratios, we employed the Nanodisc system for this study. The redox inactive form was observed to have no effect on the lyase reaction, while reactions with the normal heme-iron containing cyt b5 were enhanced ?5 fold as compared to reactions in the absence of cyt b5. We also performed resonance Raman measurements on ferric CYP17A1 bound to Mn-b5. Upon addition of Mn-b5 to Nanodisc reconstituted CYP17A1, we observed clear evidence for the formation of a b5-CYP17A1 complex, as noted by changes in the porphyrin modes and alteration in the proximal FeS vibrational frequency. Thus, although Mn-b5 binds to CYP17A1, it is unable to enhance the lyase reaction, strongly suggesting that cyt b5 has a redox effector role in enhancement of the CYP17A1 mediated lyase reaction necessary for androgen synthesis.

Dataset Information

Xenopus laevis CYP17 regulates androgen biosynthesis independent of the cofactor cytochrome b5.

Publications

Xenopus laevis CYP17 regulates androgen biosynthesis independent of the cofactor cytochrome b5.

Similar Datasets

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