Menaquinone (MK) or vitamin K2 is an important metabolite that controls the redox/energy status of Mycobacterium tuberculosis Although the major steps of MK biosynthesis have been delineated, the regulatory mechanisms of this pathway have not been adequately explored. Bashiri et al. now demonstrate that MenD, catalyzing the first committed step of MK production, is allosterically inhibited by a downstream cytosolic metabolite in the MK biosynthesis pathway.