Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, CO 80309, USA.
Structure. 2010 Nov 10;18(11):1492-501. doi: 10.1016/j.str.2010.08.012.
Folding and insertion of β-barrel outer membrane proteins (OMPs) is essential for Gram-negative bacteria. This process is mediated by the multiprotein complex BAM, composed of the essential β-barrel OMP BamA and four lipoproteins (BamBCDE). The periplasmic domain of BamA is key for its function and contains five "polypeptide transport-associated" (POTRA) repeats. Here, we report the crystal structure of the POTRA4-5 tandem, containing the essential for BAM complex formation and cell viability POTRA5. The domain orientation observed in the crystal is validated by solution NMR and SAXS. Using previously determined structures of BamA POTRA1-4, we present a spliced model of the entire BamA periplasmic domain validated by SAXS. Solution scattering shows that conformational flexibility between POTRA2 and 3 gives rise to compact and extended conformations. The length of BamA in its extended conformation suggests that the protein may bridge the inner and outer membranes across the periplasmic space.
β-桶状外膜蛋白（OMP）的折叠和插入对于革兰氏阴性菌至关重要。这个过程是由多蛋白复合物 BAM 介导的，BAM 由必需的β-桶状 OMP BamA 和四个脂蛋白（BamBCDE）组成。BamA 的周质结构域对于其功能至关重要，包含五个“多肽转运相关”（POTRA）重复序列。在这里，我们报告了 POTRA4-5 串联体的晶体结构，其中包含对于 BAM 复合物形成和细胞活力至关重要的 POTRA5。在晶体中观察到的结构取向通过溶液 NMR 和 SAXS 得到验证。利用先前确定的 BamA POTRA1-4 结构，我们提出了整个 BamA 周质结构域的拼接模型，该模型通过 SAXS 得到验证。溶液散射表明，POTRA2 和 3 之间的构象灵活性导致了紧凑和扩展的构象。在其扩展构象中，BamA 的长度表明该蛋白可能在周质空间中横跨内膜和外膜。
