Small-Molecule Probes Reveal Esterases with Persistent Activity in Dormant and Reactivating Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) is the deadliest bacterial pathogen in the
world. An estimated one-third of humans harbor Mtb in a dormant state. These asymptomatic, latent infections impede
tuberculosis eradication due to the long-term potential for reactivation.
Dormant Mtb has reduced enzymatic activity, but hydrolases
that remain active facilitate pathogen survival. We targeted Mtb esterases, a diverse set of enzymes in the serine hydrolase
family, and studied their activities using both activity-based probes
(ABPs) and fluorogenic esterase substrates. These small-molecule probes
revealed functional esterases in active, dormant, and reactivating
cultures. Using ABPs, we identified five esterases that remained active
in dormant Mtb, including LipM (Rv2284), LipN (Rv2970c),
CaeA (Rv2224c), Rv0183, and Rv1683. Three of these, CaeA, Rv0183,
and Rv1683, were catalytically active in all three culture conditions.
Fluorogenic probes additionally revealed LipH (Rv1399c), Culp1 (Rv1984c),
and Rv3036c esterase activity in dormant and active cultures. Esterases
with persistent activity are potential diagnostic biomarkers or therapeutic
targets for Mtb-infected individuals with latent
or active tuberculosis.