α-Methyl Acyl CoA Racemase Provides Mycobacterium tuberculosis Catabolic Access to Cholesterol Esters

Abstract

Metabolism of cholesterol by Mycobacterium tuberculosis (Mtb) contributes to its pathogenesis. We show that ChsE4-ChsE5 (Rv3504/Rv3505) specifically catalyzes dehydrogenation of the (25S)-3-oxo-cholest-4-en-26-oyl-CoA diastereomer in cholesterol side chain β-oxidation. Thus, a dichotomy between the supply of both 25R and 25S metabolic precursors by upstream cytochrome P450s and the substrate stereospecificity of ChsE4-ChsE5 exists. We reconcile the dilemma of 25R metabolite production by demonstrating that mycobacterial MCR (Rv1143) can efficiently epimerize C25 diastereomers of 3-oxo-cholest-4-en-26-oyl-CoA. Our data suggest that cholesterol and cholesterol ester precursors can converge into a single catabolic pathway, thus widening the metabolic niche in which Mtb survives.

Figure 1

ChsE4-ChsE5 and MCR product analysis by MALDI-TOF mass spectrometry illustrating that ChsE4-ChsE5 is stereospecific for the 25S steroyl-CoA diastereomer. a) 1:1 (25R:25S)-3-OCS-CoA substrate (top), product of ChsE4-ChsE5 catalyzed dehydrogenation (middle), product after addition of MCR to the ChsE4-ChsE5 reaction mixture (bottom). b) 7:3 (25S:25R)-Δ⁷-dafachronyl-CoA substrate (top), product of ChsE4-ChsE5 catalyzed dehydrogenation (middle), product after addition of MCR to the ChsE4-ChsE5 reaction mixture (bottom). In each case, reaction mixtures were monitored until no further changes in product distribution occurred.

Scheme 1

Mtb pathway for cholesterol activation upstream of side chain β-oxidation.