A Novel Inhibitor of the LolCDE ABC Transporter Essential for Lipoprotein Trafficking in Gram-Negative Bacteria

The outer membrane is an essential structural component of Gram-negative bacteria that is composed of lipoproteins, lipopolysaccharides, phospholipids, and integral β-barrel membrane proteins. A dedicated machinery, called the Lol system, ensures proper trafficking of lipoproteins from the inner to the outer membrane. The LolCDE ABC transporter is the inner membrane component, which is essential for bacterial viability. Here, we report a novel pyrrolopyrimidinedione compound, G0507, which was identified in a phenotypic screen for inhibitors of <i>Escherichia coli</i> growth followed by selection of compounds that induced the extracytoplasmic σ^E stress response. Mutations in <i>lolC</i>, <i>lolD</i>, and <i>lolE</i> conferred resistance to G0507, suggesting LolCDE as its molecular target. Treatment of <i>E. coli</i> cells with G0507 resulted in accumulation of fully processed Lpp, an outer membrane lipoprotein, in the inner membrane. Using purified protein complexes, we found that G0507 binds to LolCDE and stimulates its ATPase activity. G0507 still binds to LolCDE harboring a Q258K substitution in LolC (LolC_Q258K), which confers high-level resistance to G0507 <i>in vivo</i> but no longer stimulates ATPase activity. Our work demonstrates that G0507 has significant promise as a chemical probe to dissect lipoprotein trafficking in Gram-negative bacteria.