The unusual convergence of steroid catabolic pathways in .

, an opportunistic pathogen responsible for pulmonary infections, contains genes predicted to encode two steroid catabolic pathways: a cholesterol catabolic pathway similar to that of and a 4-androstenedione (4-AD) catabolic pathway. Consistent with this prediction, grew on both steroids. In contrast to , RHA1, and other Actinobacteria, the cholesterol and 4-AD catabolic gene clusters of the complex lack genes encoding HsaD, the -cleavage product (MCP) hydrolase.

IpdE1-IpdE2 Is a Heterotetrameric Acyl Coenzyme A Dehydrogenase That Is Widely Distributed in Steroid-Degrading Bacteria.

Steroid-degrading bacteria, including (), utilize an architecturally distinct subfamily of acyl coenzyme A dehydrogenases (ACADs) for steroid catabolism. These ACADs are αβ heterotetramers that are usually encoded by adjacent like genes. In mycobacteria, and (formerly and ) occur in divergently transcribed operons associated with the catabolism of 3aα--4α(3'-propanoate)-7aβ-methylhexahydro-1,5-indanedione (HIP), a steroid metabolite.

IpdAB, a virulence factor in , is a cholesterol ring-cleaving hydrolase.

() grows on host-derived cholesterol during infection. IpdAB, found in all steroid-degrading bacteria and a determinant of pathogenicity, has been implicated in the hydrolysis of the last steroid ring. Phylogenetic analyses revealed that IpdAB orthologs form a clade of CoA transferases (CoTs).

Catabolism of the Last Two Steroid Rings in and Other Bacteria.

Most mycolic acid-containing actinobacteria and some proteobacteria use steroids as growth substrates, but the catabolism of the last two steroid rings has yet to be elucidated. In , this pathway includes virulence determinants and has been proposed to be encoded by the KstR2-regulated genes, which include a predicted coenzyme A (CoA) transferase gene () and an acyl-CoA reductase gene (). In the presence of cholesterol, Δ and Δ mutants of either or strain RHA1 accumulated previously undescribed metabolites: 3aα--4α(carboxyl-CoA)-5-hydroxy-7aβ-methylhexahydro-1-indanone (5-OH HIC-CoA) and ()-2-(2-carboxyethyl)-3-methyl-6-oxocyclohex-1-ene-1-carboxyl-CoA (COCHEA-CoA), respectively.

The Structure of the Transcriptional Repressor KstR in Complex with CoA Thioester Cholesterol Metabolites Sheds Light on the Regulation of Cholesterol Catabolism in Mycobacterium tuberculosis.

Cholesterol can be a major carbon source forMycobacterium tuberculosisduring infection, both at an early stage in the macrophage phagosome and later within the necrotic granuloma. KstR is a highly conserved TetR family transcriptional repressor that regulates a large set of genes responsible for cholesterol catabolism. Many genes in this regulon, includingkstR, are either induced during infection or are essential for survival ofM.

Novel inhibitors of cholesterol degradation in Mycobacterium tuberculosis reveal how the bacterium's metabolism is constrained by the intracellular environment.

Mycobacterium tuberculosis (Mtb) relies on a specialized set of metabolic pathways to support growth in macrophages. By conducting an extensive, unbiased chemical screen to identify small molecules that inhibit Mtb metabolism within macrophages, we identified a significant number of novel compounds that limit Mtb growth in macrophages and in medium containing cholesterol as the principle carbon source. Based on this observation, we developed a chemical-rescue strategy to identify compounds that target metabolic enzymes involved in cholesterol metabolism.

Structural and functional characterization of a ketosteroid transcriptional regulator of Mycobacterium tuberculosis.

Catabolism of host cholesterol is critical to the virulence of Mycobacterium tuberculosis and is a potential target for novel therapeutics. KstR2, a TetR family repressor (TFR), regulates the expression of 15 genes encoding enzymes that catabolize the last half of the cholesterol molecule, represented by 3aα-H-4α(3'-propanoate)-7aβ-methylhexahydro-1,5-indane-dione (HIP). Binding of KstR2 to its operator sequences is relieved upon binding of HIP-CoA.

Functional analyses of three acyl-CoA synthetases involved in bile acid degradation in Pseudomonas putida DOC21.

Pseudomonas putida DOC21, a soil-dwelling proteobacterium, catabolizes a variety of steroids and bile acids. Transposon mutagenesis and bioinformatics analyses identified four clusters of steroid degradation (std) genes encoding a single catabolic pathway. The latter includes three predicted acyl-CoA synthetases encoded by stdA1, stdA2 and stdA3 respectively.

Actinobacterial acyl coenzyme A synthetases involved in steroid side-chain catabolism.

Bacterial steroid catabolism is an important component of the global carbon cycle and has applications in drug synthesis. Pathways for this catabolism involve multiple acyl coenzyme A (CoA) synthetases, which activate alkanoate substituents for β-oxidation. The functions of these synthetases are poorly understood.

FadD3 is an acyl-CoA synthetase that initiates catabolism of cholesterol rings C and D in actinobacteria.

The cholesterol catabolic pathway occurs in most mycolic acid-containing actinobacteria, such as Rhodococcus jostii RHA1, and is critical for Mycobacterium tuberculosis (Mtb) during infection. FadD3 is one of four predicted acyl-CoA synthetases potentially involved in cholesterol catabolism. A ΔfadD3 mutant of RHA1 grew on cholesterol to half the yield of wild-type and accumulated 3aα-H-4α(3'-propanoate)-7aβ-methylhexahydro-1,5-indanedione (HIP), consistent with the catabolism of half the steroid molecule.