科研之友
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摘要
In BtuB, the Escherichia coli TonB-dependent transporter for vitamin B-12, substrate binding to the extracellular surface unfolds a conserved energy coupling motif termed the Ton box into the periplasm. This transmembrane signaling event facilitates an interaction between BtuB and the inner-membrane protein TonB. In this study, continuous-wave and pulse electron paramagnetic resonance in a native outer-membrane preparation demonstrate that signaling also occurs from the periplasmic to the extracellular surface in BtuB. The binding of a TonB fragment to the periplasmic interface alters the configuration of the second extracellular loop and partially dissociates a spin-labeled substrate analog. Moreover, mutants in the periplasmic Ton box that are transport-defective alter the binding site for vitamin B-12 in BtuB. This work demonstrates that the Ton box and the extracellular substrate binding site are allosterically coupled in BtuB, and that TonB binding may initiate a partial round of transport.
- 出版日期2016-11-1
