Effect of cholesterol on phosphate uptake by human red blood cells

2019

Biophysical Journal

Anion exchanger 1 (AE1) is responsible for the exchange of bicarbonate and chloride across the erythrocyte plasma membrane. Human AE1 consists of a cytoplasmic and a membrane domain joined by a 33-residue flexible linker. Crystal structures of the individual domains have been determined, but the intact AE1 structure remains elusive. In this study, we use molecular dynamics simulations and modeling to build intact AE1 structures in a complex lipid bilayer that resembles the native erythrocyte plasma membrane. AE1 models were evaluated using available experimental data to provide an atomistic view of the interaction and dynamics of the cytoplasmic domain, the membrane domain, and the connecting linker in a complete model of AE1 in a lipid bilayer. Anionic lipids were found to interact strongly with AE1 at specific amino acid residues that are linked to diseases and blood group antigens. Cholesterol was found in the dimeric interface of AE1, suggesting that it may regulate subunit interactions and anion transport.

Section: Discussionmentioning

confidence: 99%

Molecular Simulations of Intact Anion Exchanger 1 Reveal Specific Domain and Lipid Interactions

Vecchis

2019

Biophysical Journal

“…A strong interaction of spin-labelled cholesterol with Band 3 has also been demonstrated [ 45 ]. Enriching cholesterol in red blood cells inhibits transport, while depleting cholesterol enhances transport [ 49 ]. Thus, cholesterol interaction with Band 3 modulates its transport activity, likely by rigidifying the dimer interface.…”

Section: Discussionmentioning

confidence: 99%

“…EPR measurements on ghost membranes indicated a strong interaction of spin-labelled cholesterol with Band 3 [ 45 ]. Enriched levels of cholesterol in erythrocytes deceased anion transport activity perhaps by restricting the conformational change in Band 3 that occurs during transport [ 49 ]. Band 3 interacts strongly with cholesterol and is proposed to contain a high affinity inhibitory cholesterol-binding site [ 44 , 46 ].…”

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

2018

PLoS Comput Biol

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.

“…In addition, the MD simulation studies have also suggested that there is enough space in the dimer interface for one phospholipid or sphingomyelin molecule. Cholesterol is known to inhibit anion transport and so may also play a regulatory role (Gregg and Reithmeier, 1983). Although Band 3 interacted with both 1-palmitoyl-2-oleoyl-phosphatidylserine (POPS) and phosphatidylinositol 4,5-bisphosphate (PIP 2 ) lipids, MD simulations have shown a strong preference for PIP 2 lipids.…”

Section: Band 3-lipid Interactionsmentioning

confidence: 99%

Organization and Dynamics of the Red Blood Cell Band 3 Anion Exchanger SLC4A1: Insights From Molecular Dynamics Simulations

2022

Front. Physiol.

Molecular dynamics (MD) simulations have provided new insights into the organization and dynamics of the red blood cell Band 3 anion exchanger (AE1, SLC4A1). Band 3, like many solute carriers, works by an alternating access mode of transport where the protein rapidly (104/s) changes its conformation between outward and inward-facing states via a transient occluded anion-bound intermediate. While structural studies of membrane proteins usually reveal valuable structural information, these studies provide a static view often in the presence of detergents. Membrane transporters are embedded in a lipid bilayer and associated lipids play a role in their folding and function. In this review, we highlight MD simulations of Band 3 in realistic lipid bilayers that revealed specific lipid and protein interactions and were used to re-create a model of the Wright (Wr) blood group antigen complex of Band 3 and Glycophorin A. Current MD studies of Band 3 and related transporters are focused on describing the trajectory of substrate binding and translocation in real time. A structure of the intact Band 3 protein has yet to be achieved experimentally, but cryo-electron microscopy in combination with MD simulations holds promise to capture the conformational changes associated with anion transport in exquisite molecular detail.