Ebselen Inactivates Essential Mycoplasmopsis bovis Proteins

Mycoplasmopsis bovis contributes to a variety of infectious diseases in cattle that limit meat and milk production, motivating significant antimicrobial use to prevent animal and economic loss. Currently approved antimicrobial treatments for M. bovis are ineffective or becoming so due to adaptive antimicrobial resistance (AMR). Thus, to discover alternatives to these therapies, we screened a drug repurposing library of ∼2800 compounds as antibiotics, resulting in the prioritization of ebselen (Eb) for study. The ability of Eb to prevent M. bovis growth could be ascribed to the covalent modification and inhibition of key metabolic targets, including lactate dehydrogenase (Ldh), enolase (Eno) and elongation factor G. The identification, validation, and consequences of covalent modifications by Eb at specific sites in Ldh and Eno were determined using mass spectrometry and steady-state kinetic experiments. Specifically, non-catalytic cysteine residues that are modified by Eb - Ldh Cys124 and Eno Cys216 - result in enzyme inactivation with low micromolar IC50 values. The poorly conserved Eb modification sites in M. bovis offer an opportunity for future narrow-spectrum therapeutic development for this major agricultural pathogen.