Flexibility in the ABC transporter MsbA: Alternating access with a twist

Ward, Andrew B.; Reyes, C.; Yu, Jodie; Roth, Christopher B.; Chang, Geoffrey

doi:10.1073/pnas.0709388104

Cited by 724 publications

(1,099 citation statements)

References 68 publications

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“…From the viewpoint of structures, ABC transporters that utilize the alternating access mechanism are believed to undergo large conformational changes upon ATP binding and hydrolysis (Dawson & Locher, 2006; Ward et al , 2007), whereas McjD so far appeared to be more “rigid” (Bountra et al , 2017). So far, our only evidence that McjD adopts an outward‐open conformation was from transport data using a cross‐linked TMD between TMs1‐2 and TMs1′‐2′ (Bountra et al , 2017).…”

Section: Discussion and Outlookmentioning

confidence: 99%

“…Here, we probed the opening of the McjD TMD by smFRET by placing FRET labels at TM1 and 1′. MsbA adopts the expected outward‐open conformation in the presence of nucleotides by movement of TMs1‐2 toward the opposite protomer that causes subunit intertwining (Ward et al , 2007). Our detergent data revealed that the TMD of McjD does not adopt an outward‐open conformation in the presence of nucleotides alone consistent with our previous PELDOR experiments (Fig 2C; Bountra et al , 2017).…”

Section: Discussion and Outlookmentioning

confidence: 99%

“…All ABC transporters share a common architecture consisting of a transmembrane domain (TMD) for substrate recognition and transport, and a nucleotide‐binding domain (NBD) that converts the chemical energy of ATP into conformational changes for transport (Beis, 2015). The structures of several homodimeric (Dawson & Locher, 2006; Ward et al , 2007; Perez et al , 2015) and heterodimeric ABC transporters (Hohl et al , 2012; Noll et al , 2017) revealed distinct conformations and suggest, in combination with biophysical studies (e.g., EPR and NMR; Dong et al , 2005; Zou et al , 2009; Bountra et al , 2017; Timachi et al , 2017; Barth et al , 2018), that they undergo large conformational changes during transport. Their complex architecture is, however, a fundamental hurdle to fully understand the coupling between conformational changes, substrate binding, ATP binding and hydrolysis, and transport.…”

Section: Introductionmentioning

confidence: 99%

“…Based on the available structural, biophysical, and biochemical data for exporters, two transport mechanisms have been proposed, the alternating access mechanism (Dawson & Locher, 2006; Ward et al , 2007; Choudhury et al , 2014; Bountra et al , 2017) and the outward‐only mechanism (Perez et al , 2015). ABC exporters that use the alternating access mechanism switch between inward‐ and outward‐facing states with transmembrane helices intertwining, which exposes the ligand binding site alternatively to the inside or outside of the membrane, a process that is believed to be coupled to ATP binding to hydrolysis.…”

Section: Introductionmentioning

confidence: 99%

“…ABC transporters that utilize the alternating access mechanism undergo large conformational changes during the transport cycle suggested by crystal structures (Ward et al , 2007) and EPR‐based Double Electron Electron Resonance (DEER) measurements (Dong et al , 2005; Borbat et al , 2007; Mishra et al , 2014) of the lipid A flippase MsbA from Escherichia coli . Although the DEER measurements proposed that ATP triggers the opening of the TMD to the periplasmic side for release of the substrate, it is unclear how precisely these changes are coupled to ATP binding and hydrolysis.…”

Section: Introductionmentioning

confidence: 99%

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Conformational dynamics of the ABC transporter McjD seen by single‐molecule FRET

et al. 2018

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ABC transporters utilize ATP for export processes to provide cellular resistance against toxins, antibiotics, and harmful metabolites in eukaryotes and prokaryotes. Based on static structure snapshots, it is believed that they use an alternating access mechanism, which couples conformational changes to ATP binding (outward‐open conformation) and hydrolysis (inward‐open) for unidirectional transport driven by ATP. Here, we analyzed the conformational states and dynamics of the antibacterial peptide exporter McjD from Escherichia coli using single‐molecule Förster resonance energy transfer (smFRET). For the first time, we established smFRET for an ABC exporter in a native‐like lipid environment and directly monitor conformational dynamics in both the transmembrane‐ (TMD) and nucleotide‐binding domains (NBD). With this, we unravel the ligand dependences that drive conformational changes in both domains. Furthermore, we observe intrinsic conformational dynamics in the absence of ATP and ligand in the NBDs. ATP binding and hydrolysis on the other hand can be observed via NBD conformational dynamics. We believe that the progress made here in combination with future studies will facilitate full understanding of ABC transport cycles.

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Section: Discussion and Outlookmentioning

confidence: 99%

Section: Discussion and Outlookmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Conformational dynamics of the ABC transporter McjD seen by single‐molecule FRET

et al. 2018

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Cancer Drug Resistance: Targets and Therapies

Zdrazil

Ecker

2010

Burger's Medicinal Chemistry and Drug Discovery

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What monomeric nucleotide binding domains can teach us about dimeric ABC proteins

Ford

Hellmich

2020

FEBS Letters

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The classic conceptualization of ATP binding cassette (ABC) transporter function is an ATP‐dependent conformational change coupled to transport of a substrate across a biological membrane via the transmembrane domains (TMDs). The binding of two ATP molecules within the transporter's two nucleotide binding domains (NBDs) induces their dimerization. Despite retaining the ability to bind nucleotides, isolated NBDs frequently fail to dimerize. ABC proteins without a TMD, for example ABCE and ABCF, have NBDs tethered via elaborate linkers, further supporting that NBD dimerization does not readily occur for isolated NBDs. Intriguingly, even in full‐length transporters, the NBD‐dimerized, outward‐facing state is not as frequently observed as might be expected. This leads to questions regarding what drives NBD interaction and the role of the TMDs or linkers. Understanding the NBD–nucleotide interaction and the subsequent NBD dimerization is thus pivotal for understanding ABC transporter activity in general. Here, we hope to provide new insights into ABC protein function by discussing the perplexing issue of (missing) NBD dimerization in isolation and in the context of full‐length ABC proteins.

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Flexibility in the ABC transporter MsbA: Alternating access with a twist

Abstract: lipid flippase ͉ membrane protein structure ͉ multidrug transport

Cited by 724 publications

References 68 publications

Conformational dynamics of the ABC transporter McjD seen by single‐molecule FRET

Conformational dynamics of the ABC transporter McjD seen by single‐molecule FRET

Cancer Drug Resistance: Targets and Therapies

What monomeric nucleotide binding domains can teach us about dimeric ABC proteins

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