Structure of the membrane-pore-forming fragment of colicin A
Structure of the membrane-pore-forming fragment of colicin A
复制标题
大肠杆菌素 A 膜孔形成片段的结构
作者：
M. Parker;F. Pattus;A. Tucker;D. Tsernoglou
粘菌素是由敏感的大肠杆菌及其密切相关的细菌产生并对其具有活性的抗生素蛋白。它们可以吸附在敏感细胞外膜外表面的特定受体上，然后转移到这些细胞内的特定靶标上。粘菌素中最大的一类是那些能在细胞膜上形成电压依赖性通道，从而破坏细胞能量潜力的粘菌素。大肠杆菌素分子在结构域中被组织起来，每个结构域携带一种与毒素致死活性相关的功能。成孔活性似乎位于羧基端。由大肠杆菌素A的氨基酸389-592组成的热解片段具有与整个分子非常相似的成孔特性。该片段可溶于水介质，并自发插入脂质双分子层。我们通过x射线晶体学和2.5 Å分辨率的细化确定了大肠杆菌素A的成孔片段的结构。该蛋白由十个α-螺旋组成，呈三层结构。其中两个螺旋完全埋在结构中，形成一个疏水发夹环，类似于在易位中起作用的信号序列。我们提出了一个蛋白质插入脂质双分子层的模型，其特征可能适用于其他涉及蛋白质插入或跨膜易位的生物系统。
Colicins are antibiotic proteins produced by and active against sensitive Eschericia coli and closely related bacteria. They can adsorb to specific receptors located at the external surface of the outer membrane of sensitive cells, and are then translocated to their specific targets within these cells. The largest group of colicins comprises those which can form voltage-dependent channels in membranes, thereby destroying the cell's energy potential1. Colicin molecules are organized in structural domains, each domain carrying one function associated with the toxin's lethal activity. The pore-forming activity seems to be located at the carboxyl terminus. A thermolytic fragment comprising amino acids 389–592 from colicin A has pore-forming properties very similar to those of the entire molecule. This fragment is soluble in aqueous medium and spontaneously inserts into lipid bilayers2. We have determined the structure of the pore-forming fragment of colicin A by X-ray crystallography and refinement at 2.5 Å resolution. The protein consists of ten α-helices organized in a three-layer structure. Two of the helices are completely buried within the structure and form a hydrophobic hairpin loop similar to that proposed for signal sequences which function in translocation. We present a model for insertion of the protein into lipid bilayers the features of which may be applicable in other biological systems involving protein insertion or translocation across membranes.
影响因子：
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作者：
B. C. Wang
通讯作者：
B. C. Wang