ABC transporters: a riddle wrapped in a mystery inside an enigma

Jones, Peter M.; O’Mara, Megan L.; George, Anthony M.

doi:10.1016/j.tibs.2009.06.004

Cited by 156 publications

(138 citation statements)

References 92 publications

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“…1B) reveals an inward rotation of the helical subdomain toward the RecA-like subdomain, as seen in many isolated NBD structures upon ATP binding (5)(6)(7)(8). These two subdomains are connected by the Q-loop (27) that lines part of the cleft surrounding the coupling helix of the transmembrane domains MalF and MalG. The Q-loop is expected to undergo conformational changes upon subdomain rotation that might be detected as a change in mobility of an attached spin label (SL).…”

Section: Resultsmentioning

confidence: 94%

Dynamics of α-helical subdomain rotation in the intact maltose ATP-binding cassette transporter

Orelle

Alvarez²,

Oldham³

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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ATP-binding cassette (ABC) transporters are powered by a nucleotide-binding domain dimer that opens and closes during cycles of ATP hydrolysis. These domains consist of a RecA-like subdomain and an α-helical subdomain that is specific to the family. Many studies on isolated domains suggest that the helical subdomain rotates toward the RecA-like subdomain in response to ATP binding, moving the family signature motif into a favorable position to interact with the nucleotide across the dimer interface. Moreover, the transmembrane domains are docked into a cleft at the interface between these subdomains, suggesting a putative role of the rotation in interdomain communication. Electron paramagnetic resonance spectroscopy was used to study the dynamics of this rotation in the intact Escherichia coli maltose transporter MalFGK 2 . This importer requires a periplasmic maltose-binding protein (MBP) that activates ATP hydrolysis by promoting the closure of the cassette dimer (MalK 2 ). Whereas this rotation occurred during the transport cycle, it required not only trinucleotide, but also MBP, suggesting it is part of a global conformational change in the transporter. Interaction of AMP-PNP-Mg 2þ and a MBP that is locked in a closed conformation induced a transition from open MalK 2 to semiopen MalK 2 without significant subdomain rotation. Inward rotation of the helical subdomain and complete closure of MalK 2 therefore appear to be coupled to the reorientation of transmembrane helices and the opening of MBP, events that promote transfer of maltose into the transporter. After ATP hydrolysis, the helical subdomain rotates out as MalK 2 opens, resetting the transporter in an inward-facing conformation.EPR spectroscopy | transport mechanism | membrane protein A TP-binding cassette (ABC) transporters belong to one of the largest protein superfamilies in organisms, and mediate the translocation of a wide range of substrates across the membrane (1). These transporters typically contain two transmembrane domains (TMDs) and are energized by a nucleotide-binding domain (NBD) dimer that closes and opens during cycles of ATP binding and hydrolysis (2, 3). Each NBD consists of a RecA-like subdomain, found in numerous ATPases (4), and an α-helical subdomain that is specific to the ABC family (5). Crystallographic studies (5-8) and molecular dynamic simulations (9, 10), performed on isolated NBDs, suggest that the helical subdomain rotates toward the RecA-like subdomain in response to ATP binding. This rotation positions the ABC family signature motif to interact with nucleotide across the dimer interface so that the NBDs can close to hydrolyze ATP. After ATP hydrolysis, it is suggested that the helical subdomain rotates away (5, 11). In addition, the TMDs contact the NBDs at the interface between these subdomains (12-15), suggesting a putative role of the rotation in interdomain communication (16). Here, we used sitedirected spin labeling electron paramagnetic resonance (EPR) spectroscopy (17,18) to study the dynamics of this rotation...

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Section: Resultsmentioning

confidence: 94%

Dynamics of α-helical subdomain rotation in the intact maltose ATP-binding cassette transporter

Orelle

Alvarez²,

Oldham³

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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“…prokaryotes (1)(2)(3). In humans, the isoform ABCB1, also known as P-glycoprotein (P-gp), is an efflux transporter that contributes to cancer cell drug resistance (4 -6), and this has made it a target for therapeutics that modulate the effectiveness of many anti-cancer drugs.…”

mentioning

confidence: 99%

Conformational Analysis of Human ATP-binding Cassette Transporter ABCB1 in Lipid Nanodiscs and Inhibition by the Antibodies MRK16 and UIC2

Ritchie

Kwon

Atkins

2011

Journal of Biological Chemistry

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Background: P-glycoprotein plays a role in drug resistance and drug interactions. Results: Surface plasmon resonance with P-glycoprotein in lipid nanodiscs indicates that inhibitory antibodies uncouple the ATP hydrolysis of P-gp from its transport function. Conclusion: Inhibitory antibodies do not prevent P-gp flux through the catalytic cycle, but rather block drug efflux without inhibiting ATP hydrolysis. Significance: The results clarify the mechanism of inhibitory antibodies to P-gp.

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“…In the periplasm, MBP binds maltose, which stabilizes a change from an "open" to a "closed" conformation, enabling it to stimulate the MalFGK 2 ATPase (5,6). Interactions with closed, maltose-bound MBP lead to exposure of the MalFGK 2 maltose-binding site to the periplasmic side where maltose can move from MBP into an occluded translocation pathway (7,8).…”

mentioning

confidence: 99%

“…After ATP hydrolysis, the transporter returns its binding site to the cytoplasmic face to allow the substrate to enter the cytoplasm. This is known as the alternating access model of maltose transport (4) and may be a common mechanism among ABC transporters (2,9,10).…”

mentioning

confidence: 99%

Studies of the Maltose Transport System Reveal a Mechanism for Coupling ATP Hydrolysis to Substrate Translocation without Direct Recognition of Substrate

Gould

Shilton

2010

Journal of Biological Chemistry

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The ATPase activity of the maltose transporter (MalFGK 2 ) is dependent on interactions with the maltose-binding protein (MBP). To determine whether direct interactions between the translocated sugar and MalFGK 2 are important for the regulation of ATP hydrolysis, we used an MBP mutant (sMBP) that is able to bind either maltose or sucrose. We observed that maltose-and sucrose-bound sMBP stimulate equal levels of MalFGK 2 ATPase activity. Therefore, the ATPase activity of MalFGK 2 is coupled to translocation of maltose solely by interactions between MalFGK 2 and MBP. For both maltose and sucrose, the ability of sMBP to stimulate the ATP-binding cassette (ABC)2 transporters move various substrates across membranes, with substrate movement coupled to the hydrolysis of ATP. Although the ATPase activity of ABC exporters like P-glycoprotein is generally stimulated by substrate binding, the ATPase activity of ABC importers is activated by a peripheral substrate-binding protein and not the free substrate (for recent reviews see Refs.

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ABC transporters: a riddle wrapped in a mystery inside an enigma

Cited by 156 publications

References 92 publications

Dynamics of α-helical subdomain rotation in the intact maltose ATP-binding cassette transporter

Dynamics of α-helical subdomain rotation in the intact maltose ATP-binding cassette transporter

Conformational Analysis of Human ATP-binding Cassette Transporter ABCB1 in Lipid Nanodiscs and Inhibition by the Antibodies MRK16 and UIC2

Studies of the Maltose Transport System Reveal a Mechanism for Coupling ATP Hydrolysis to Substrate Translocation without Direct Recognition of Substrate

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