Substrate Analogues Entering the Lipoic Acid Salvage Pathway via Lipoate-Protein Ligase 2 Interfere with Staphylococcus aureus Virulence

Lipoic acid (LA) is an essential cofactor in prokaryotic
and eukaryotic
organisms, required for the function of several multienzyme complexes
such as oxoacid dehydrogenases. Prokaryotes either synthesize LA or
salvage it from the environment. The salvage pathway in Staphylococcus aureus includes two lipoate-protein
ligases, LplA1 and LplA2, as well as the amidotransferase LipL. In
this study, we intended to hijack the salvage pathway by LA analogues
that are transferred via LplA2 and LipL to the E2 subunits of various
dehydrogenases, thereby resulting in nonfunctional enzymes that eventually
impair viability of the bacterium. Initially, a virtual screening
campaign was carried out to identify potential LA analogues that bind
to LplA2. Three selected compounds affected S. aureus USA300 growth in minimal medium at concentrations ranging from 2.5
to 10 μg/mL. Further analysis of the most potent compound (Lpl-004) revealed its transfer to E2 subunits of dehydrogenase
complexes and a negative impact on its functionality. Growth impairment
caused by Lpl-004 treatment was restored by adding products
of the lipoate-dependent enzyme complexes. In addition, Caenorhabditis elegans infected with LpL-004-treated USA300 demonstrated a significantly expanded lifespan compared
to worms infected with untreated bacteria. Our results provide evidence
that LA analogues exploiting the LA salvage pathway represent an innovative
strategy for the development of novel antimicrobial substances.