Asymmetry of inverted-topology repeats in the AE1 anion exchanger suggests an elevator-like mechanism

Ficici, Emel; Faraldo‐Gómez, José D.; Jennings, Michael L.; Forrest, Lucy R.

doi:10.1085/jgp.201711836

Cited by 35 publications

(45 citation statements)

References 99 publications

(154 reference statements)

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“…VcINDY likely undergoes multiple large-and small-scale conformational changes during transport. There are now many examples of structurally characterised transporters that are predicted to employ an elevator-like transport mechanism 24,[29][30][31][32][33][34][35][36][37][38] , which has revealed common features amongst many of them, including; distinct scaffold and transport domains, a broken transmembrane helix containing an intramembrane loop that contributes to the substrate binding site, and two re-entrant hairpin loops that enter the membrane but do not fully span it. While structural differences exist between the predicted elevatortype transporters, they are all predicted (or have been shown) to undergo a substantial vertical translocation of the transport domain, usually accompanied by a pronounced rotation of this domain, to expose the substrate binding site to both sides of the membrane.…”

Section: Discussionmentioning

confidence: 99%

Solvent accessibility changes in a Na+-dependent C4-dicarboxylate transporter suggest differential substrate effects in a multistep mechanism

Sampson

Stewart

Mindell

et al. 2020

Journal of Biological Chemistry

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The divalent anion sodium symporter (DASS) family (SLC13) play critical roles in metabolic homeostasis, influencing many processes including fatty acid synthesis, insulin resistance, and adiposity. DASS transporters catalyse the Na+-driven concentrative uptake of Krebs cycle intermediates and sulfate into cells; disrupting their function can protect against age-related metabolic diseases and can extend lifespan. An inward-facing crystal structure and an outward-facing model of a bacterial DASS family member, VcINDY from Vibrio cholerae, predict an elevator-like transport mechanism involving a large rigid body movement of the substrate binding site. How substrate binding influences the conformational state of VcINDY is currently unknown. Here, we probe the interaction between substrate binding and protein conformation by monitoring substrate-induced solvent accessibility changes of broadly distributed positions in VcINDY using a site-specific alkylation strategy. Our findings reveal that accessibility to all positions tested are modulated by the presence of substrates, with the majority becoming less accessible in the presence of saturating concentrations of both Na+ and succinate. We also observe separable effects of Na+ and succinate binding at several positions suggesting distinct effects of the two substrates. Furthermore, accessibility changes to a solely succinate-sensitive position suggests that substrate binding is a low affinity, ordered process. Mapping these accessibility changes onto the structures of VcINDY suggests that Na+ binding drives the transporter into an as-yet-unidentified conformational state, involving rearrangement of the substrate binding site-associated re-entrant hairpin loops. These findings provide insight into the mechanism of VcINDY, which is currently the only structural-characterised representative of the entire DASS family.

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Section: Discussionmentioning

confidence: 99%

Solvent accessibility changes in a Na+-dependent C4-dicarboxylate transporter suggest differential substrate effects in a multistep mechanism

Sampson

Stewart

Mindell

et al. 2020

Journal of Biological Chemistry

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“…It is the relative movement of these two sub-domains that provides the alternating access to the central anion binding site [ 25 ]. The molecular details of this movement have yet to be established, likely operating in rocker-switch or elevator mode [ 26 – 28 ]. The dimer is held together by a central 4-helix bundle with predominant interactions at the extra-cellular ends of TM5 and 6, however there is significant space in the dimer interface of the crystal structure.…”

Section: Introductionmentioning

confidence: 99%

Interaction of the human erythrocyte Band 3 anion exchanger 1 (AE1, SLC4A1) with lipids and glycophorin A: Molecular organization of the Wright (Wr) blood group antigen

Kalli

Reithmeier

2018

PLoS Comput Biol

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The Band 3 (AE1, SLC4A1) membrane protein is found in red blood cells and in kidney where it functions as an electro-neutral chloride/bicarbonate exchanger. In this study, we have used molecular dynamics simulations to provide the first realistic model of the dimeric membrane domain of human Band 3 in an asymmetric lipid bilayer containing a full complement of phospholipids, including phosphatidylinositol 4,5–bisphosphate (PIP2) and cholesterol, and its partner membrane protein Glycophorin A (GPA). The simulations show that the annular layer in the inner leaflet surrounding Band 3 was enriched in phosphatidylserine and PIP2 molecules. Cholesterol was also enriched around Band 3 but also at the dimer interface. The interaction of these lipids with specific sites on Band 3 may play a role in the folding and function of this anion transport membrane protein. GPA associates with Band 3 to form the Wright (Wr) blood group antigen, an interaction that involves an ionic bond between Glu658 in Band 3 and Arg61 in GPA. We were able to recreate this complex by performing simulations to allow the dimeric transmembrane portion of GPA to interact with Band 3 in a model membrane. Large-scale simulations showed that the GPA dimer can bridge Band 3 dimers resulting in the dynamic formation of long strands of alternating Band 3 and GPA dimers.

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“…The structures of dimeric SLC4 and SLC23 proteins in different conformations 17,18,19,21,22 all hold identical, yet family-specific, contact surfaces. This is further supported by repeat-swap homology modeling of AE1, which indicated that no changes in the dimerization interface were required during the transition from the outwardfacing structure to the inward-facing model 23 . Transitions between interfaces seem further unlikely due to the requirement for significant rearrangements in structural elements, such as the cytoplasmic region following TM12 in SLC4A1 and SLC4A4, which also appears stable and blocking alternative interfaces in SLC26Dg (Suppl.…”

Section: Discussionmentioning

confidence: 64%

“…A mounting body of evidence 16,19,22,23 suggests that these proteins operate based on an elevator alternating-access mode of transport 24 involving a rigid body translation-rotation of the core domain with respect to the gate domain. Dimeric states have been previously observed for pro-and eukaryotic members of the SLC4 25,26,27 , SLC23 28 , and SLC26 4,29,30,31,32 families.…”

Section: Introductionmentioning

confidence: 99%

Structural basis for functional interactions in dimers of SLC26 transporters

Chang

Jaumann

Reichel

et al. 2019

Preprint

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The SLC26 family of transporters maintains anion equilibria in all kingdoms of life. The family shares a 7 + 7 transmembrane segments inverted repeat architecture with the SLC4 and SLC23 families, but holds a regulatory STAS domain in addition. While the only experimental SLC26 structure is monomeric, SLC26 proteins form structural and functional dimers in the lipid membrane. Here we resolve the structure of an SLC26 dimer embedded in a lipid membrane and characterize its functional relevance by combining PELDOR distance measurements and biochemical studies with MD simulations and spin-label ensemble refinement. Our structural model reveals a unique interface different from the SLC4 and SLC23 families. The functionally relevant STAS domain exerts a stabilizing effect on regions central in this dimer. Characterization of heterodimers indicates that protomers in the dimer functionally interact. The combined structural and functional data define the framework for a mechanistic understanding of functional cooperativity in SLC26 dimers.

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Asymmetry of inverted-topology repeats in the AE1 anion exchanger suggests an elevator-like mechanism

Cited by 35 publications

References 99 publications

Solvent accessibility changes in a Na+-dependent C4-dicarboxylate transporter suggest differential substrate effects in a multistep mechanism

Solvent accessibility changes in a Na+-dependent C4-dicarboxylate transporter suggest differential substrate effects in a multistep mechanism

Interaction of the human erythrocyte Band 3 anion exchanger 1 (AE1, SLC4A1) with lipids and glycophorin A: Molecular organization of the Wright (Wr) blood group antigen

Structural basis for functional interactions in dimers of SLC26 transporters

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