Ghosh P, Mel S F, Stroud R M
Department of Biochemistry and Biophysics, University of California, San Francisco 94143-0448, USA.
Nat Struct Biol. 1994 Sep;1(9):597-604. doi: 10.1038/nsb0994-597.
Colicin Ia undergoes a transition from a soluble to a transmembrane state, forming an ion channel to effect its bactericidal activity. The X-ray crystal structure of soluble colicin Ia at an effective resolution of 4 A reveals that the molecule is highly alpha-helical and has an unusually elongated 'Y'-shape. The stalk and two arms of the 'Y' form three discrete structural domains which most likely correspond to the three functional regions identified for the channel-forming colicins. The channel-forming region of colicin Ia can be located to the larger of the two arms, the insertion domain, by its structural similarity to the ten alpha-helix motif found for the ion channel-forming fragments of colicins A and E1. The domain arrangement found in this structure provides novel insights into the mechanism of membrane insertion of colicin Ia.
大肠杆菌素Ia经历从可溶状态到跨膜状态的转变，形成离子通道以实现其杀菌活性。有效分辨率为4埃的可溶大肠杆菌素Ia的X射线晶体结构表明，该分子高度α-螺旋，呈异常细长的“Y”形。“Y”的茎和两个臂形成三个离散的结构域，这很可能对应于为形成通道的大肠杆菌素确定的三个功能区域。通过与大肠杆菌素A和E1的离子通道形成片段中发现的十个α-螺旋基序的结构相似性，大肠杆菌素Ia的通道形成区域可以定位到两个臂中较大的那个，即插入结构域。此结构中发现的结构域排列为大肠杆菌素Ia的膜插入机制提供了新的见解。
