Cryo-EM analyses unveil details of mechanism and targocil-II mediated inhibition of S. aureus WTA transporter TarGH

Wall teichoic acid (WTA) is a polyol phosphate polymer that covalently decorates peptidoglycan of gram-positive bacteria, including Staphylococcus aureus. Central to WTA biosynthesis is flipping of lipid-linked precursors across the cell membrane by TarGH, a type V ABC transporter. Here, we present cryo-EM structures of S. aureus TarGH in the presence of targocil-II, a promising small-molecule lead with β-lactam antibiotic synergistic action. Targocil-II binds to the extracellular dimerisation interface of TarG, we suggest mimicking flipped but not yet released substrate. In absence of targocil-II and in complex with ATP analogue ATPγS, determined at 2.3 Å resolution, the ATPase active site is allosterically inhibited. This is due to a so far undescribed D-loop conformation, potentially minimizing spurious ATP hydrolysis in the absence of substrate. Targocil-II binding comparatively causes local and remote conformational changes through to the TarH active site, with the D-loop now optimal for ATP hydrolysis. These structures suggest an ability to modulate ATP hydrolysis in a WTA substrate dependent manner and a jammed ATPase cycle as the basis of the observed inhibition by targocil-II. The molecular insights provide an unprecedented basis for development of TarGH targeted therapeutics for treatment of multidrug-resistant S. aureus and other gram-positive bacterial infections.