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  • Title: Single-molecule visualization of conformational changes and substrate transport in the vitamin B12 ABC importer BtuCD-F.
    Author: Goudsmits JMH, Slotboom DJ, van Oijen AM.
    Journal: Nat Commun; 2017 Nov 21; 8(1):1652. PubMed ID: 29162829.
    Abstract:
    ATP-binding cassette (ABC) transporters form the largest class of active membrane transport proteins. Binding and hydrolysis of ATP by their highly conserved nucleotide-binding domains drive conformational changes of the complex that mediate transport of substrate across the membrane. The vitamin B12 importer BtuCD-F in Escherichia coli is an extensively studied model system. The periplasmic soluble binding protein BtuF binds the ligand; the transmembrane and ATPase domains BtuCD mediate translocation. Here we report the direct observation at the single-molecule level of ATP, vitamin B12 and BtuF-induced events in the transporter complex embedded in liposomes. Single-molecule fluorescence imaging techniques reveal that membrane-embedded BtuCD forms a stable complex with BtuF, regardless of the presence of ATP and vitamin B12. We observe that a vitamin B12 molecule remains bound to the complex for tens of seconds, during which several ATP hydrolysis cycles can take place, before it is being transported across the membrane.
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