Lipopolysaccharides (LPS) are essential envelope components in many Gram‐negative bacteria and provide intrinsic resistance to antibiotics. LPS molecules are synthesized in the inner membrane and then transported to the cell surface by the LPS transport (Lpt) machinery. In this system, the ATP‐binding cassette (ABC) transporter LptB₂FGC extracts LPS from the inner membrane and places it onto a periplasmic protein bridge through a poorly understood mechanism. Here, we show that residue E86 of LptB is essential for coupling the function of this ATPase to that of its partners LptFG, specifically at the step where ATP binding drives the closure of the LptB dimer and the collapse of the LPS‐binding cavity in LptFG that moves LPS to the Lpt periplasmic bridge. We also show that defects caused by changing residue E86 are suppressed by mutations altering either LPS structure or transmembrane helices in LptG. Furthermore, these suppressors also fix defects in the coupling helix of LptF, but not of LptG. Together, these results support a transport mechanism in which the ATP‐driven movements of LptB and those of the substrate‐binding cavity in LptFG are bi‐directionally coordinated through the rigid‐body coupling, with LptF’s coupling helix being important in coordinating cavity collapse with LptB dimerization.

中文翻译：

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LptB-LptF偶联通过刚体机制介导LptB2FGC转运蛋白中底物结合腔的关闭以提取LPS

脂多糖 (LPS) 是许多革兰氏阴性菌中必不可少的包膜成分，对抗生素具有内在抗性。LPS 分子在内膜中合成，然后通过 LPS 转运 (Lpt) 机制转运到细胞表面。在该系统中，ATP 结合盒 (ABC) 转运蛋白 LptB ₂FGC extracts LPS from the inner membrane and places it onto a periplasmic protein bridge through a poorly understood mechanism. Here, we show that residue E86 of LptB is essential for coupling the function of this ATPase to that of its partners LptFG, specifically at the step where ATP binding drives the closure of the LptB dimer and the collapse of the LPS‐binding cavity in LptFG that moves LPS to the Lpt periplasmic bridge. We also show that defects caused by changing residue E86 are suppressed by mutations altering either LPS structure or transmembrane helices in LptG. Furthermore, these suppressors also fix defects in the coupling helix of LptF, but not of LptG. Together, these results support a transport mechanism in which the ATP‐driven movements of LptB and those of the substrate‐binding cavity in LptFG are bi‐directionally coordinated through the rigid‐body coupling, with LptF’s coupling helix being important in coordinating cavity collapse with LptB dimerization.