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A Step-by-step Method for the Reconstitution of an ABC Transporter into Nanodisc Lipid Particles
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Energy Coupling Efficiency in the Type I ABC Transporter GlnPQ
Jelger A Lycklama A Nijeholt1, Ruslan Vietrov1, Gea K Schuurman-Wolters1
1Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747, AG, Groningen, The Netherlands; Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747, AG, Groningen, The Netherlands.
Journal of Molecular Biology
|February 13, 2018
Summary
Understanding ATP binding cassette (ABC) importers reveals substrate binding and ATP-driven transport. This study clarifies the energy coupling efficiency and mechanism of GlnPQ, an ABC transporter.
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- ATP binding cassette (ABC) importers facilitate solute transport through receptor-mediated substrate binding and ATP-driven translocation.
- The precise initiation, coupling mechanisms, and ATP stoichiometry of ABC transporter cycles remain debated.
Purpose of the Study:
- To elucidate the mechanism of solute transport and energy coupling efficiency in the ABC importer GlnPQ.
- To determine the role of substrate binding in initiating transport and the ATP hydrolysis stoichiometry.
Main Methods:
- Reconstitution of the GlnPQ ABC importer in nanodiscs and proteoliposomes.
- Single-molecule Förster resonance energy transfer (smFRET) to determine substrate-binding domain (SBD) conformational states.
- Measurement of substrate-dependent and independent ATP hydrolysis and transmembrane transport.
Main Results:
- Basal ATPase activity is primarily driven by the docking of closed-unliganded SBDs onto the GlnPQ transporter domain.
- Arginine binds both SBDs but does not induce their closing, unlike glutamine.
- The stoichiometry of ATP consumed per transported substrate is approximately two.
Conclusions:
- The study clarifies the mechanism of transport initiation and energy coupling in ABC importers with covalently linked SBDs.
- Findings provide insights into the function of GlnPQ and Type I ABC importers generally.
- The stoichiometry of ~2 ATP per substrate highlights the energy efficiency of the transport process.
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