Department of Protein Evolution, Max Planck Institute for Developmental Biology, Spemannstrasse 35, Tübingen 72076, Germany.
J Biol Chem. 2011 Aug 5;286(31):27792-803. doi: 10.1074/jbc.M111.238931. Epub 2011 May 17.
In Escherichia coli, a multicomponent BAM (β-barrel assembly machinery) complex is responsible for recognition and assembly of outer membrane β-barrel proteins. The functionality of BAM in protein biogenesis is mainly orchestrated through the presence of two essential components, BamA and BamD. Here, we present crystal structures of four lipoproteins (BamB-E). Monomeric BamB and BamD proteins display scaffold architectures typically implied in transient protein interactions. BamB is a β-propeller protein comprising eight WD40 repeats. BamD shows an elongated fold on the basis of five tetratricopeptide repeats, three of which form the scaffold for protein recognition. The rod-shaped BamC protein has evolved through the gene duplication of two conserved domains known to mediate protein interactions in structurally related complexes. By contrast, the dimeric BamE is formed through a domain swap and indicates fold similarity to the β-lactamase inhibitor protein family, possibly integrating cell wall stability in BAM function. Structural and biochemical data show evidence for the specific recognition of amphipathic sequences through the tetratricopeptide repeat architecture of BamD. Collectively, our data advance the understanding of the BAM complex and highlight the functional importance of BamD in amphipathic outer membrane β-barrel protein motif recognition and protein delivery.
在大肠杆菌中，一个多组分的 BAM（β-桶状膜装配机制）复合物负责识别和装配外膜β-桶状膜蛋白。BAM 在蛋白质生物发生中的功能主要通过两个必需成分 BamA 和 BamD 的存在来协调。在这里，我们呈现了四个脂蛋白（BamB-E）的晶体结构。单体 BamB 和 BamD 蛋白显示出通常暗示在瞬时蛋白相互作用中的支架架构。BamB 是一个由八个 WD40 重复组成的β-类 propeller 蛋白。BamD 基于五个 tetratricopeptide 重复形成一个伸长的折叠，其中三个形成用于蛋白质识别的支架。棒状 BamC 蛋白通过两个保守结构域的基因复制进化而来，这些结构域已知在结构相关的复合物中介导蛋白质相互作用。相比之下，二聚体 BamE 是通过结构域交换形成的，并且与β-内酰胺酶抑制剂蛋白家族具有折叠相似性，可能在 BAM 功能中整合细胞壁稳定性。结构和生化数据表明 BamD 的 tetratricopeptide 重复结构可以特异性识别两亲性序列。总的来说，我们的数据推进了对 BAM 复合物的理解，并强调了 BamD 在两亲性外膜β-桶状膜蛋白基序识别和蛋白质输送中的功能重要性。
