Background and Purpose: With the emergence of extensively drug-resistant tuberculosis there is a need for new anti-tubercular drugs that work through novel mechanisms of action. The meta cleavage product hydrolase, HsaD, has been demonstrated to be critical to the survival of Mycobacterium tuberculosis in macrophages and is encoded in an operon involved in cholesterol catabolism, which is identical in M. tuberculosis and M. bovis BCG.
Experimental Approach: We generated a mutant strain of M. bovis BCG with a deletion of hsaD and tested its growth on cholesterol. Using a fragment based approach, over 1,000 compounds were screened by a combination of differential scanning fluorimetry, NMR spectroscopy and enzymatic assay with pure recombinant HsaD to identify potential inhibitors. We used enzymological and structural studies to investigate derivatives of inhibitors identified and to test their effects on growth of M. bovis BCG and M. tuberculosis.
Key Results: The hsaD deleted strain is unable to grow on cholesterol as sole carbon source but can grow on glucose. Of seven chemically distinct "hits" from the library, two chemical classes of fragments were found to bind in the vicinity of the active siteof HsaD by X-ray crystallography. The compounds also inhibited growth of M. tuberculosis on cholesterol. The most potent inhibitor of HsaD was found also to be the best inhibitor of mycobacterial growth on cholesterol-supplemented minimal medium.
Conclusions and Implicatioins: We propose that HsaD is a novel therapeutic target which should be fully exploited in order to design and discover new anti-tubercular drugs.
- Journal article