Substrate-induced asymmetry coordinates lipoprotein handover and abaucin trapping in Acinetobacter baumannii LolDF

The homodimeric lipoprotein transporter LolDF supports outer-membrane biogenesis in Acinetobacter baumannii. How homodimeric LolDF generates directional lipoprotein transport, and how the reported two- and four-abaucin states are related, remain unclear. Using defined lipidated AbLolB and AbLolA, we show that substrate binding breaks LolF symmetry: LolFB primarily accommodates the lipid anchor, LolFA positions the adjacent polypeptide, and LolA docks asymmetrically through the LolF hook and an AbLolA-specific loop. C1 reconstruction of the wide abaucin state reveals non-equivalent central ligands, whereas C2 processing of the same particles averages this asymmetry; the two peripheral ligands form a stable inhibitory core, while the central sites are conditionally occupied in the expanded cavity. Abaucin inhibits ATPase activity and LolA-mediated transfer from substrate-associated LolDF, supporting a unified mechanism in which substrate-induced asymmetry organizes productive handover and its conformational plasticity is redirected during inhibition.