Kurisu Genji, Zakharov Stanislav D, Zhalnina Mariya V, Bano Sufiya, Eroukova Veronika Y, Rokitskaya Tatiana I, Antonenko Yuri N, Wiener Michael C, Cramer William A
Department of Biological Sciences, Purdue University, Lilly Hall of Life Sciences, 915 W. State St., West Lafayette, Indiana 47907-1392, USA.
Nat Struct Biol. 2003 Nov;10(11):948-54. doi: 10.1038/nsb997. Epub 2003 Oct 5.
Cellular import of colicin E3 is initiated by the Escherichia coli outer membrane cobalamin transporter, BtuB. The 135-residue 100-A coiled-coil receptor-binding domain (R135) of colicin E3 forms a 1:1 complex with BtuB whose structure at a resolution of 2.75 A is reported. Binding of R135 to the BtuB extracellular surface (DeltaG(o) = -12 kcal mol(-1)) is mediated by 27 residues of R135 near the coiled-coil apex. Formation of the R135-BtuB complex results in unfolding of R135 N- and C-terminal ends, inferred to be important for unfolding of the colicin T-domain. Small conformational changes occur in the BtuB cork and barrel domains but are insufficient to form a translocation channel. The absence of a channel and the peripheral binding of R135 imply that BtuB serves to bind the colicin, and that the coiled-coil delivers the colicin to a neighboring outer membrane protein for translocation, thus forming a colicin translocon. The translocator was concluded to be OmpF from the occlusion of OmpF channels by colicin E3.
大肠杆菌外膜钴胺素转运蛋白BtuB启动了大肠杆菌素E3的细胞内导入。报道了大肠杆菌素E3的135个残基、100埃的卷曲螺旋受体结合结构域（R135）与BtuB形成的1:1复合物，其分辨率为2.75埃的结构。R135与BtuB细胞外表面的结合（ΔG⁰ = -12千卡/摩尔）由卷曲螺旋顶端附近的R135的27个残基介导。R135-BtuB复合物的形成导致R135 N端和C端展开，推测这对大肠杆菌素T结构域的展开很重要。BtuB的软木塞和桶状结构域发生了小的构象变化，但不足以形成转运通道。没有通道以及R135的外周结合意味着BtuB用于结合大肠杆菌素，并且卷曲螺旋将大肠杆菌素递送至相邻的外膜蛋白进行转运，从而形成大肠杆菌素转位子。从大肠杆菌素E3对OmpF通道的封闭得出转位子是OmpF的结论。
