Mechanism-based inactivator of isocitrate lyases 1 and 2 from <i>Mycobacterium tuberculosis</i>

Isocitrate lyase (ICL, types 1 and 2) is the first enzyme of the glyoxylate shunt, an essential pathway for <i>Mycobacterium tuberculosis</i> (<i>Mtb</i>) during the persistent phase of human TB infection. Here, we report 2-vinyl-d-isocitrate (2-VIC) as a mechanism-based inactivator of <i>Mtb</i> ICL1 and ICL2. The enzyme-catalyzed retro-aldol cleavage of 2-VIC unmasks a Michael substrate, 2-vinylglyoxylate, which then forms a slowly reversible, covalent adduct with the thiolate form of active-site Cys₁₉₁ 2-VIC displayed kinetic properties consistent with covalent, mechanism-based inactivation of ICL1 and ICL2 with high efficiency (partition ratio, <1). Analysis of a complex of ICL1:2-VIC by electrospray ionization mass spectrometry and X-ray crystallography confirmed the formation of the predicted covalent <i>S</i>-homopyruvoyl adduct of the active-site Cys₁₉₁.