The substrate-binding protein imposes directionality on an electrochemical sodium gradient-driven TRAP transporter |
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| Authors: | Christopher Mulligan Eric R. Geertsma Emmanuele Severi David J. Kelly Bert Poolman Gavin H. Thomas |
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| Affiliation: | aDepartment of Biology (Area 10), University of York, P.O. Box 373, York YO10 5YW, United Kingdom; ;bDepartment of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands; and ;cDepartment of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, United Kingdom |
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| Abstract: | Substrate-binding protein-dependent secondary transporters are widespread in prokaryotes and are represented most frequently by members of the tripartite ATP-independent periplasmic (TRAP) transporter family. Here, we report the membrane reconstitution of a TRAP transporter, the sialic acid-specific SiaPQM system from Haemophilus influenzae, and elucidate its mechanism of energy coupling. Uptake of sialic acid via membrane-reconstituted SiaQM depends on the presence of the sialic acid-binding protein, SiaP, and is driven by the electrochemical sodium gradient. The interaction between SiaP and SiaQM is specific as transport is not reconstituted using the orthologous sialic acid-binding protein VC1779. Importantly, the binding protein also confers directionality on the transporter, and reversal of sialic acid transport from import to export is only possible in the presence of an excess of unliganded SiaP. |
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| Keywords: | sialic acid SiaPQM tripartite ATP-independent periplasmic transporter Haemophilus influenzae receptor-dependent translocation |
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