Identification of Novel Intein Inhibitors with Relevance to Tuberculosis

Inteins are naturally occurring protein elements that autocatalytically excise themselves from a non-functional precursor and ligate the flanking protein segments with a peptide bond, resulting in a functional protein.  Inteins interrupt three proteins important for the viability of Mycobacterium tuberculosis.  Preventing intein splicing, and thus the formation of functional post-processed proteins, suggests that intein inhibition may be used as a novel anti-mycobacterial strategy (M. Belfort, US Patent, 5,795,731).  Due to the growing problem of multiple drug-resistant tuberculosis infections, such alternatives to traditional antibiotic regimens are especially appealing.  It has been shown that cisplatin, an FDA approved anti-cancer drug, is a potent inhibitor of intein splicing, both in vitro and in vivo (Zhang et al. (2011) JBC, 286, 1277).  Due to its high toxicity, however, cisplatin has limited clinical value as an anti-mycobacterial.  Structural and mechanistic insights gained from studies with the Mtu RecA intein were applied in a virtual screen using the Autodock suite of docking software (http://autodock.scripps.edu/), designed to identify compounds that retained potent inhibition activity while minimizing the toxicity displayed by cisplatin. The lead compounds from the virtual screen were then tested for inhibition activity in vitro using a fluorescent splicing reporter.  This study is laying the groundwork for potential de novo design of novel anti-microbials.