Nature Structural Biology10, 948 - 954 (2003)
Published online: 5 October 2003; | doi:10.1038/nsb997
The structure of BtuB with bound colicin E3 R-domain implies a translocon
Genji Kurisu1, 2, 6, Stanislav D Zakharov1, 3, 6, Mariya V Zhalnina1, 6, Sufiya Bano1, Veronika Y Eroukova4, Tatiana I Rokitskaya4, Yuri N Antonenko4, Michael C Wiener5
& William A Cramer1
1
Department of Biological Sciences, Purdue University, Lilly Hall of Life Sciences, 915 W. State St., West Lafayette, Indiana 47907-1392, USA.
2
Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan.
3
Institute of Basic Biological Problems, Russian Academy of Sciences, Puschino, Russia 142290.
4
Belozersky Institute, Moscow State University, Moscow, Russia 11999.
5
Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia 22908, USA.
Cellular import of colicin E3 is initiated by the Escherichia coli outer membrane cobalamin transporter, BtuB. The 135-residue 100-Å coiled-coil receptor-binding domain (R135) of colicin E3 forms a 1:1 complex with BtuB whose structure at a resolution of 2.75 Å is reported. Binding of R135 to the BtuB extracellular surface (G° = -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.
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G° = -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.
–barrels
