Biomaterial Database

Interactions between transport inhibitors at the anion binding sites of the band 3 dimer. 1981

I G Macara, and L C Cantley

Evidence is presented that the binding of aromatic disulfonates to the external transport sites of the red cell anion-exchange protein (band 3) can exhibit negative cooperativity. Fluorescence resonance energy transfer has been used to compare the affinities of an aromatic disulfonate 4,4'-bis-(4-nitro-2,1,3-benzoxadiazolyl)dihydrostilbene-2,2'-disulfonate[H2(NBD)2DS] for "empty" band 3 dimers (in which neither external transport site is occupied) and for "half-filled" dimers (in which one site per dimer is occupied by a covalently attached fluorescent stilbenedisulfonate). H2(NBD)2DS apparently binds to the external anion transport site since it is a potent inhibitor of [35S]sulfate influx into red cells (Ki = 20-50 nM), binds reversibly to approximately one site per band 3 monomer (1.6 X 10(6) sites/cell), and is displaced by covalent labeling with a disulfonic stilbene. The affinity of H2(NBD)2DS for membranes in which 80% of the transport sites are occupied by covalently attached 4-benzamido-4'-isothiocyanostilbene-2,2'-disulfonate (BIDS) was approximately 1 order of magnitude lower than that for unmodified membranes. However, when a similar proportion of the transport sites on red cells was blocked by reaction with BIDS, [35S]sulfate was taken up with a lower Vmax but with a Km identical with that observed for unmodified cells, suggesting that no subunit interactions are necessary for transport. Therefore, in order to test whether the observed negative cooperativity of aromatic disulfonate binding could be ascribed simply to steric hindrance, the distance between transport sites was measured by fluorescence resonance energy transfer. H2(NBD)2DS and eosin maleimide were used as acceptors, with BIDS as donor. Transfer efficiencies were determined by donor fluorescence quenching, by acceptor fluorescence enhancement, and from donor lifetime changes. Uncertainties in the distance were estimated from measured depolarization factors. The donor-acceptor distance was found to be only 28-52 A. Since the probes are large molecules, they could therefore be very close together, and the observed negative cooperativity might be explained by overlapping sites. The results suggest that the subunits of a band 3 dimer transport anions independently but that access to the transport sites may be provided by a cavity between the subunits.

UI	MeSH Term	Description	Entries
D008565	Membrane Proteins	Proteins which are found in membranes including cellular and intracellular membranes. They consist of two types, peripheral and integral proteins. They include most membrane-associated enzymes, antigenic proteins, transport proteins, and drug, hormone, and lectin receptors.	Cell Membrane Protein,Cell Membrane Proteins,Cell Surface Protein,Cell Surface Proteins,Integral Membrane Proteins,Membrane-Associated Protein,Surface Protein,Surface Proteins,Integral Membrane Protein,Membrane Protein,Membrane-Associated Proteins,Membrane Associated Protein,Membrane Associated Proteins,Membrane Protein, Cell,Membrane Protein, Integral,Membrane Proteins, Integral,Protein, Cell Membrane,Protein, Cell Surface,Protein, Integral Membrane,Protein, Membrane,Protein, Membrane-Associated,Protein, Surface,Proteins, Cell Membrane,Proteins, Cell Surface,Proteins, Integral Membrane,Proteins, Membrane,Proteins, Membrane-Associated,Proteins, Surface,Surface Protein, Cell
D011485	Protein Binding	The process in which substances, either endogenous or exogenous, bind to proteins, peptides, enzymes, protein precursors, or allied compounds. Specific protein-binding measures are often used as assays in diagnostic assessments.	Plasma Protein Binding Capacity,Binding, Protein
D001798	Blood Proteins	Proteins that are present in blood serum, including SERUM ALBUMIN; BLOOD COAGULATION FACTORS; and many other types of proteins.	Blood Protein,Plasma Protein,Plasma Proteins,Serum Protein,Serum Proteins,Protein, Blood,Protein, Plasma,Protein, Serum,Proteins, Blood,Proteins, Plasma,Proteins, Serum
D004735	Energy Transfer	The transfer of energy of a given form among different scales of motion. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed). It includes the transfer of kinetic energy and the transfer of chemical energy. The transfer of chemical energy from one molecule to another depends on proximity of molecules so it is often used as in techniques to measure distance such as the use of FORSTER RESONANCE ENERGY TRANSFER.	Transfer, Energy
D004910	Erythrocyte Membrane	The semi-permeable outer structure of a red blood cell. It is known as a red cell 'ghost' after HEMOLYSIS.	Erythrocyte Ghost,Red Cell Cytoskeleton,Red Cell Ghost,Erythrocyte Cytoskeleton,Cytoskeleton, Erythrocyte,Cytoskeleton, Red Cell,Erythrocyte Cytoskeletons,Erythrocyte Ghosts,Erythrocyte Membranes,Ghost, Erythrocyte,Ghost, Red Cell,Membrane, Erythrocyte,Red Cell Cytoskeletons,Red Cell Ghosts
D004912	Erythrocytes	Red blood cells. Mature erythrocytes are non-nucleated, biconcave disks containing HEMOGLOBIN whose function is to transport OXYGEN.	Blood Cells, Red,Blood Corpuscles, Red,Red Blood Cells,Red Blood Corpuscles,Blood Cell, Red,Blood Corpuscle, Red,Erythrocyte,Red Blood Cell,Red Blood Corpuscle
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D000838	Anions	Negatively charged atoms, radicals or groups of atoms which travel to the anode or positive pole during electrolysis.	Anion
D001457	Anion Exchange Protein 1, Erythrocyte	A major integral transmembrane protein of the ERYTHROCYTE MEMBRANE. It is the anion exchanger responsible for electroneutral transporting in CHLORIDE IONS in exchange of BICARBONATE IONS allowing CO2 uptake and transport from tissues to lungs by the red blood cells. Genetic mutations that result in a loss of the protein function have been associated with type 4 HEREDITARY SPHEROCYTOSIS.	Anion Transport Protein, Erythrocyte,Band 3 Protein,Erythrocyte Anion Transport Protein,Erythrocyte Membrane Band 3 Protein,AE1 Anion Exchanger,AE1 Chloride-Bicarbonate Exchanger,AE1 Cl- HCO3- Exchanger,AE1 Gene Product,Anion Exchanger 1,Antigens, CD233,Band 3 Anion Transport Protein,Band III Protein,CD233 Antigen,CD233 Antigens,Capnophorin,EPB3 Protein,Erythrocyte Anion Exchanger,Erythrocyte Membrane Anion Transport Protein,Erythrocyte Membrane Protein Band 3, Diego Blood Group,Protein Band 3,SLC4A1 Protein,Solute Carrier Family 4 Member 1,Solute Carrier Family 4, Anion Exchanger, Member 1,AE1 Chloride Bicarbonate Exchanger,AE1 Cl HCO3 Exchanger,Anion Exchanger, Erythrocyte,Antigen, CD233,Chloride-Bicarbonate Exchanger, AE1,Exchanger 1, Anion,Protein, EPB3
D001665	Binding Sites	The parts of a macromolecule that directly participate in its specific combination with another molecule.	Combining Site,Binding Site,Combining Sites,Site, Binding,Site, Combining,Sites, Binding,Sites, Combining