The outer membrane (OM) of gram-negative bacteria confers innate resistance to toxins and antibiotics. Integral β-barrel outer membrane proteins (OMPs) function to establish and maintain the selective permeability of the OM. OMPs are assembled into the OM by the β-barrel assembly machine (BAM), which is composed of one OMP—BamA—and four lipoproteins—BamB, C, D, and E. BamB, C, and E can be removed individually with only minor effects on barrier function; however, depletion of either BamA or BamD causes a global defect in OMP assembly and results in cell death. We have identified a gain-of-function mutation, bamA_E470K, that bypasses the requirement for BamD. Although bamD::kan bamA_E470K cells exhibit growth and OM barrier defects, they assemble OMPs with surprising robustness. Our results demonstrate that BamD does not play a catalytic role in OMP assembly, but rather functions to regulate the activity of BamA.

革兰氏阴性细菌的外膜（OM）赋予对毒素和抗生素的固有抗性。完整的β桶外膜蛋白（OMP）的作用是建立和维持OM的选择性通透性。OMP通过β-桶组装机（BAM）组装到OM中，该机器由一个OMP-BamA和四个脂蛋白-BamB，C，D和E组成。对屏障功能的影响很小；但是，BamA或BamD的耗尽会导致OMP装配的整体缺陷并导致细胞死亡。我们已经确定功能增益突变bamA _E470K绕过了BamD的要求。虽然bamD :: kan bamA _E470K细胞表现出生长和OM屏障缺陷，它们以惊人的坚固性组装OMP。我们的结果表明，BamD在OMP组装中不发挥催化作用，而起调节BamA活性的作用。