Bergal Hans Thor, Hopkins Alex Hunt, Metzner Sandra Ines, Sousa Marcelo Carlos
Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, CO 80309, USA.
Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, CO 80309, USA.
Structure. 2016 Feb 2;24(2):243-51. doi: 10.1016/j.str.2015.10.030. Epub 2015 Dec 31.
The β-barrel assembly machine (BAM) mediates folding and insertion of integral β-barrel outer membrane proteins (OMPs) in Gram-negative bacteria. Of the five BAM subunits, only BamA and BamD are essential for cell viability. Here we present the crystal structure of a fusion between BamA POTRA4-5 and BamD from Rhodothermus marinus. The POTRA5 domain binds BamD between its tetratricopeptide repeats 3 and 4. The interface structural elements are conserved in the Escherichia coli proteins, which allowed structure validation by mutagenesis and disulfide crosslinking in E. coli. Furthermore, the interface is consistent with previously reported mutations that impair BamA-BamD binding. The structure serves as a linchpin to generate a BAM model where POTRA domains and BamD form an elongated periplasmic ring adjacent to the membrane with a central cavity approximately 30 × 60 Å wide. We propose that nascent OMPs bind this periplasmic ring prior to insertion and folding by BAM.
β-桶组装机器（BAM）介导革兰氏阴性菌中整合β-桶外膜蛋白（OMP）的折叠与插入。在五个BAM亚基中，只有BamA和BamD对细胞活力至关重要。本文展示了来自海栖热袍菌的BamA POTRA4-5与BamD融合体的晶体结构。POTRA5结构域在其3号和4号四肽重复序列之间结合BamD。界面结构元件在大肠杆菌蛋白中保守，这使得通过在大肠杆菌中进行诱变和二硫键交联来验证结构成为可能。此外，该界面与先前报道的损害BamA-BamD结合的突变一致。该结构是构建BAM模型的关键，在该模型中，POTRA结构域和BamD在膜附近形成一个细长的周质环，中央腔宽约30×60 Å。我们提出新生的OMP在被BAM插入和折叠之前先结合这个周质环。
