Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada.
J Biol Chem. 2011 Nov 11;286(45):39116-21. doi: 10.1074/jbc.M111.298166. Epub 2011 Sep 20.
The β-barrel assembly machinery (BAM) complex of Escherichia coli is a multiprotein machine that catalyzes the essential process of assembling outer membrane proteins. The BAM complex consists of five proteins: one membrane protein, BamA, and four lipoproteins, BamB, BamC, BamD, and BamE. Here, we report the first crystal structure of a Bam lipoprotein complex: the essential lipoprotein BamD in complex with the N-terminal half of BamC (BamC(UN) (Asp(28)-Ala(217)), a 73-residue-long unstructured region followed by the N-terminal domain). The BamCD complex is stabilized predominantly by various hydrogen bonds and salt bridges formed between BamD and the N-terminal unstructured region of BamC. Sequence and molecular surface analyses revealed that many of the conserved residues in both proteins are found at the BamC-BamD interface. A series of truncation mutagenesis and analytical gel filtration chromatography experiments confirmed that the unstructured region of BamC is essential for stabilizing the BamCD complex structure. The unstructured N terminus of BamC interacts with the proposed substrate-binding pocket of BamD, suggesting that this region of BamC may play a regulatory role in outer membrane protein biogenesis.
大肠杆菌的β-桶组装机制（BAM）复合物是一种多蛋白机器，催化着外膜蛋白组装的基本过程。BAM 复合物由五个蛋白质组成：一个膜蛋白 BamA 和四个脂蛋白 BamB、BamC、BamD 和 BamE。在这里，我们报告了第一个 Bam 脂蛋白复合物的晶体结构：必需的脂蛋白 BamD 与 BamC 的 N 端半段（BamC（UN）（Asp（28）-Ala（217）），一个 73 个残基长的无结构区域，后面跟着 N 端结构域）复合。BamCD 复合物主要通过 BamD 和 BamC 的 N 端无结构区域之间形成的各种氢键和盐桥稳定。序列和分子表面分析表明，这两种蛋白质中的许多保守残基都位于 BamC-BamD 界面处。一系列截断突变和分析凝胶过滤层析实验证实，BamC 的无结构区域对于稳定 BamCD 复合物结构是必需的。BamC 的无结构 N 端与 BamD 的假定底物结合口袋相互作用，表明 BamC 的这一区域可能在外膜蛋白生物发生中起调节作用。
