Energy Coupling Efficiency in the Type I ABC Transporter GlnPQ. Issue 6 (16th March 2018)

• Record Type: Journal Article
• Authors: Lycklama a Nijeholt, Jelger A.; Vietrov, Ruslan; Schuurman-Wolters, Gea K.; Poolman, Bert
• Is Part Of: Journal of molecular biology. Volume 430:Issue 6(2018)
• Page Start: 853
• Page End: 866
• Publication Date: 2018-03-16
• Subjects: ABC importer -- substrate-binding domain -- energy coupling efficiency -- ATP/substrate stoichiometry -- Nanodiscs; SBD substrate-binding domain -- ABC ATP binding cassette -- TMD transmembrane domain -- NBD nucleotide-binding domain -- SBP substrate-binding protein -- MSP membrane scaffold protein; Molecular biology -- Periodicals; Biology -- Periodicals; Biochemistry -- Periodicals; Bacteriology -- Periodicals; Molecular Biology -- Periodicals; Biochemistry -- Periodicals; Biologie moléculaire -- Périodiques; Biologie -- Périodiques; Biochimie -- Périodiques; Moleculaire biologie; Biochemistry; Biology; Molecular biology; Periodicals; 572.805
• DOI: 10.1016/j.jmb.2018.02.001
• Languages: English
• ISSNs: 0022-2836

Abstract

Abstract: Solute transport via ATP binding cassette (ABC) importers involves receptor-mediated substrate binding, which is followed by ATP-driven translocation of the substrate across the membrane. How these steps are exactly initiated and coupled, and how much ATP it takes to complete a full transport cycle, are subject of debate. Here, we reconstitute the ABC importer GlnPQ in nanodiscs and in proteoliposomes and determine substrate-(in)dependent ATP hydrolysis and transmembrane transport. We determined the conformational states of the substrate-binding domains (SBDs) by single-molecule Förster resonance energy transfer measurements. We find that the basal ATPase activity (ATP hydrolysis in the absence of substrate) is mainly caused by the docking of the closed-unliganded state of the SBDs onto the transporter domain of GlnPQ and that, unlike glutamine, arginine binds both SBDs but does not trigger their closing. Furthermore, comparison of the ATPase activity in nanodiscs with glutamine transport in proteoliposomes shows that the stoichiometry of ATP per substrate is close to two. These findings help understand the mechanism of transport and the energy coupling efficiency in ABC transporters with covalently linked SBDs, which may aid our understanding of Type I ABC importers in general. Graphical Abstract: Highlights: The closed state of the substrate-binding domains initiates the ATP hydrolysis cycle in the ABC importer GlnPQ. ATP hydrolysis and glutamine transport are tightly coupled. The ATP/substrate stoichiometry is 2. Arginine binds to both substrate-binding domains but does not trigger closing of the receptor proteins.