Functional Redundancy of Steroid C26-monooxygenase Activity in Mycobacterium tuberculosis Revealed by Biochemical and Genetic Analyses

Paul R. Ortiz de Montellano,Jonathan B. Johnston,Hugues Ouellet

doi:10.1074/jbc.m110.161117

Paul R. Ortiz de Montellano, Jonathan B. Johnston + Show 1 more

Open Access

https://doi.org/10.1074/jbc.m110.161117

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Abstract

One challenge to the development of new antitubercular drugs is the existence of multiple virulent strains that differ genetically. We and others have recently demonstrated that CYP125A1 is a steroid C(26)-monooxygenase that plays a key role in cholesterol catabolism in Mycobacterium tuberculosis CDC1551 but, unexpectedly, not in the M. tuberculosis H37Rv strain. This discrepancy suggests that the H37Rv strain possesses compensatory activities. Here, we examined the roles in cholesterol metabolism of two other cytochrome P450 enzymes, CYP124A1 and CYP142A1. In vitro analysis, including comparisons of the binding affinities and catalytic efficiencies, demonstrated that CYP142A1, but not CYP124A1, can support the growth of H37Rv cells on cholesterol in the absence of cyp125A1. All three enzymes can oxidize the sterol side chain to the carboxylic acid state by sequential oxidation to the alcohol, aldehyde, and acid. Interestingly, CYP125A1 generates oxidized sterols of the (25S)-26-hydroxy configuration, whereas the opposite 25R stereochemistry is obtained with CYP124A1 and CYP142A1. Western blot analysis indicated that CYP124A1 was not detectably expressed in either the H37Rv or CDC1551 strains, whereas CYP142A1 was found in H37Rv but not CDC1551. Genetic complementation of CDC1551 Δcyp125A1 cells with the cyp124A1 or cyp142A1 genes revealed that the latter can fully rescue the growth defect on cholesterol, whereas cells overexpressing CYP124A1 grow poorly and accumulate cholest-4-en-3-one. Our data clearly establish a functional redundancy in the essential C(26)-monooxygenase activity of M. tuberculosis and validate CYP125A1 and CYP142A1 as possible drug targets.

Highlights

To proliferate within the macrophages, M. tuberculosis cells undergo a shift in metabolism from using carbohydrates to primarily utilizing host lipids [3,4,5]
Expression of Native Steroid C26-monooxygenase(s) in M. tuberculosis Cells—As a second step in identifying the compensatory steroid C26-monooxygenase activity lacking in CDC1551 ⌬cyp125A1 cells, we examined the endogenous levels of CYP125A1, CYP124A1, and CYP142A1 and the inducibility of their expression by C27 steroids in both the CDC1551 and H37Rv strains
We examine the ability of two M. tuberculosis cytochrome P450 enzymes, CYP124A1 and CYP142A1, to compensate for loss of CYP125A1 as a steroid C26-monooxygenase in two different clinical isolates, CDC1551 and H37Rv, using a combination of biochemical and genetic experiments

Summary

EXPERIMENTAL PROCEDURES

Materials—All solvents and reagents were of the highest purity commercially available unless noted otherwise. Methyl␤-cyclodextrin, glucose 6-phosphate, Tween 20, glucose-6phosphate dehydrogenase (Saccharomyces cerevisiae), ferredoxin (Spinacea oleracea), ferredoxin NADPϩ reductase (S. oleracea), cholesterol oxidase (Streptomyces sp.), cholesterol, cholest-4-en-3-one, ergosterol, and tyloxapol were purchased from Sigma. (25R)-26-Hydroxycholesterol and (25S)-26hydroxycholesterol were purchased from Research Plus (Barnegat, NJ). Cholest-4-en-3-one-(25S)-carboxylic acid was obtained from Avanti Polar Lipids (Alabaster, AL). Polyclonal antibodies to purified M. tuberculosis CYP124A1, CYP125A1, and CYP142A1 were raised in rabbits (Pacific Immunology, Ramona, CA). Expression, and Purification—The CYP124A1, CYP125A1, and CYP142A1 enzymes from M. tuberculosis H37Rv were cloned, expressed in Escherichia coli, and purified as described previously [21, 24].

The abbreviations used are

RESULTS

DISCUSSION