Inhibiting mycobacterial tryptophan synthase by targeting the inter-subunit interface

• Published in: Scientific reports 2017-08, Vol.7 (1), p.9430-15, Article 9430
• Main Authors: Abrahams, Katherine A., Cox, Jonathan A. G., Fütterer, Klaus, Rullas, Joaquín, Ortega-Muro, Fátima, Loman, Nicholas J., Moynihan, Patrick J., Pérez-Herrán, Esther, Jiménez, Elena, Esquivias, Jorge, Barros, David, Ballell, Lluís, Alemparte, Carlos, Besra, Gurdyal S.
• Format: Article
• Language: English
• Subjects: 45/23; 631/154/555; 631/154/556; 631/326; 631/45/535/1266; 64/60; 82/16; 82/83; Amino acids; Animal models; Antitubercular Agents - pharmacology; Bacterial Proteins - antagonists & inhibitors; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Crystal structure; Drug discovery; Drug Resistance, Bacterial; Enzyme Inhibitors - pharmacology; Enzymes; Gene mapping; Humanities and Social Sciences; Humans; Microbial Sensitivity Tests; Models, Molecular; multidisciplinary; Mutation; Mycobacterium - drug effects; Mycobacterium - enzymology; Mycobacterium - genetics; Overexpression; Protein Conformation; Reproductive fitness; Resistant mutant; Science; Science (multidisciplinary); Structure-Activity Relationship; Sulfolane; Sulfonamides; Thiophenes - pharmacology; Tryptophan; Tryptophan synthase; Tryptophan Synthase - antagonists & inhibitors; Tryptophan Synthase - chemistry; Tryptophan Synthase - metabolism; Tuberculosis
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-017-09642-y

Drug discovery efforts against the pathogen Mycobacterium tuberculosis ( Mtb ) have been advanced through phenotypic screens of extensive compound libraries. Such a screen revealed sulfolane 1 and indoline-5-sulfonamides 2 and 3 as potent inhibitors of mycobacterial growth. Optimization in the sulfolane series led to compound 4 , which has proven activity in an in vivo murine model of Mtb infection. Here we identify the target and mode of inhibition of these compounds based on whole genome sequencing of spontaneous resistant mutants, which identified mutations locating to the essential α- and β-subunits of tryptophan synthase. Over-expression studies confirmed tryptophan synthase as the biological target. Biochemical techniques probed the mechanism of inhibition, revealing the mutant enzyme complex incurs a fitness cost but does not prevent inhibitor binding. Mapping of the resistance conferring mutations onto a low-resolution crystal structure of Mtb tryptophan synthase showed they locate to the interface between the α- and β-subunits. The discovery of anti-tubercular agents inhibiting tryptophan synthase highlights the therapeutic potential of this enzyme and draws attention to the prospect of other amino acid biosynthetic pathways as future Mtb drug targets.