Chak K F, Safo M K, Ku W Y, Hsieh S Y, Yuan H S
Institute of Biochemistry, National Yang-Ming University, Taipei, Taiwan, Republic of China.
Proc Natl Acad Sci U S A. 1996 Jun 25;93(13):6437-42. doi: 10.1073/pnas.93.13.6437.
The immunity protein of colicin E7 (ImmE7) can bind specifically to the DNase-type colicin E7 and inhibit its bactericidal activity. Here we report the 1.8-angstrom crystal structure of the ImmE7 protein. This is the first x-ray structure determined in the superfamily of colicin immunity proteins. The ImmE7 protein consists of four antiparallel alpha-helices, folded in a topology similar to the architecture of a four-helix bundle structure. A region rich in acidic residues is identified. This negatively charged area has the greatest variability within the family of DNase-type immunity proteins; thus, it seems likely that this area is involved in specific binding to colicin. Based on structural, genetic, and kinetic data, we suggest that all the DNase-type immunity proteins, as well as colicins, share a "homologous-structural framework" and that specific interaction between a colicin and its cognate immunity protein relies upon how well these two proteins' charged residues match on the interaction surface, thus leading to specific immunity of the colicin.
大肠杆菌素E7免疫蛋白（ImmE7）能特异性结合核酸酶型大肠杆菌素E7并抑制其杀菌活性。在此，我们报道了ImmE7蛋白1.8埃的晶体结构。这是在大肠杆菌素免疫蛋白超家族中确定的首个X射线结构。ImmE7蛋白由四个反平行α螺旋组成，其折叠拓扑结构类似于四螺旋束结构的架构。鉴定出一个富含酸性残基的区域。这个带负电荷的区域在核酸酶型免疫蛋白家族中具有最大的变异性；因此，该区域似乎可能参与与大肠杆菌素的特异性结合。基于结构、遗传和动力学数据，我们认为所有核酸酶型免疫蛋白以及大肠杆菌素都共享一个“同源结构框架”，并且大肠杆菌素与其同源免疫蛋白之间的特异性相互作用取决于这两种蛋白的带电荷残基在相互作用表面上的匹配程度，从而导致大肠杆菌素的特异性免疫。
