The Crystal Structure of Escherichia coli Group 4 Capsule Protein GfcC Reveals a Domain Organization Resembling That of Wza
The Crystal Structure of Escherichia coli Group 4 Capsule Protein GfcC Reveals a Domain Organization Resembling That of Wza
复制标题
DOI：
10.1021/bi101869h
复制
发表时间：
2011-06-21
期刊：
影响因子：
2.9
通讯作者：
Saper, Mark A.
中科院分区：
文献类型：
--
作者：
Sathiyamoorthy, Karthik;Mills, Erez;Saper, Mark A.
我们报告的1.9埃分辨率晶体结构的肠致病性大肠杆菌GfcC，周质蛋白编码的gfc操纵子，这是必不可少的4组多糖胶囊（O-抗原胶囊）的装配。gfcC的假定基因直系同源物存在于至少29种革兰氏阴性菌属的荚膜编码区中。GfcC是DUF 1017家族的成员，由串联β-抓握（泛素样）结构域（D2和D3）和羧基末端两亲性螺旋组成，该结构域排列使人联想到Wza的结构域排列，其形成用于组1胶囊输出的出口孔。与来自Wza的跨膜C-末端螺旋不同，GfcC C-末端螺旋对D3进行包装。以前在β-抓取结构域结构中未观察到的是D2中的48个残基的螺旋发夹插入物，其与D3结合，限制其位置并隔离羧基末端的两亲性螺旋。一个位于中心的和不变的Arg 115不仅是必要的适当的本地化，但也形成了两个最保守的口袋之一。最后，我们绘制了一个GfcC蛋白融合到外膜β-桶孔在一些物种和分泌生物膜形成胞外多糖所需的融合蛋白之间的类比。
We report the 1.9 angstrom resolution crystal structure of enteropathogenic Escherichia colt GfcC, a periplasmic protein encoded by the gfc operon, which is essential for assembly of group 4 polysaccharide capsule (O-antigen capsule). Presumed gene orthologs of gfcC are present in capsule-encoding regions of at least 29 genera of Gram-negative bacteria. GfcC, a member of the DUF1017 family, is comprised of tandem beta-grasp (ubiquitin-like) domains (D2 and D3) and a carboxyl-terminal amphipathic helix, a domain arrangement reminiscent of that of Wza that forms an exit pore for group 1 capsule export. Unlike the membrane-spanning C-terminal helix from Wza, the GfcC C-terminal helix packs against D3. Previously unobserved in a beta-grasp domain structure is a 48-residue helical hairpin insert in D2 that binds to D3, constraining its position and sequestering the carboxyl-terminal amphipathic helix. A centrally located and invariant Arg115 not only is essential for proper localization but also forms one of two mostly conserved pockets. Finally, we draw analogies between a GfcC protein fused to an outer membrane beta-barrel pore in some species and fusion proteins necessary for secreting biofilm-forming exopolysaccharides.