scholarly journals Anion Transport Using Core Functionalized Hyperbranched Polymers and Evidence of a Dense Packed Limit Based on Molecular Weight

Molecules ◽  
2021 ◽  
Vol 26 (22) ◽  
pp. 6850
Author(s):  
Sozan Najib Abdullah ◽  
Georgia Mann ◽  
Lance J. Twyman
Keyword(s):  
Binding Site ◽  
Organic Phase ◽  
Environmental Science ◽  
Anion Transport ◽  
Anion Binding ◽  
Ordered Structures ◽  
Dendritic Polymer ◽  
Toxic Materials ◽  
Transport Species ◽  
Specific Species

Being able to bind, select, and transport species is central to a number of fields, including medicine, materials, and environmental science. In particular, recognizing a specific species from one phase and transporting it across, or into another phase, has obvious applications in environ-mental science, for example, removal of unwanted or toxic materials from an aqueous or organic phase. In this paper, we describe an approach that uses a functionalized dendritic polymer to bind and transport a small anionic molecule across an organic phase (and between two aqueous phases). The design was based on encapsulation principles borrowed from nature, where anions are bound and transported by proteins that have specific sites within their globular ordered structures. For the work reported here, a globular dendritic polymer functionalized with an isophthalamide-based receptor was used to replace the protein structure and anion-binding site. Along with control experiments, the binding and transport properties of two functionalized HBPs were assessed using a Pressman U tube experiment. Both HBPs demonstrated an enhanced ability to bind and transport anions (when compared to the anion-binding site used in isolation). Furthermore, optimum binding and transport occurred when the smaller of the two HBPs were used. This supports our previous observations regarding the existence of a dense packed limit for HBPs.

scholarly journals The human erythrocyte anion transport protein, band 3. Characterization of exofacial alkaline titratable groups involved in anion binding/translocation.

1992 ◽  
Vol 100 (2) ◽  
pp. 301-339 ◽  
Author(s):  
P J Bjerrum
Keyword(s):  
Ionic Strength ◽  
Binding Site ◽  
Transport System ◽  
Human Erythrocyte ◽  
Binding Constant ◽  
Anion Transport ◽  
High Ionic Strength ◽  
Anion Binding ◽  
Asymmetry Factor ◽  
Sensitive Group

Chloride self-exchange across the human erythrocyte membrane at alkaline extracellular pH (pHO) and constant neutral intracellular pH (pH(i)) can be described by an exofacial deprotonatable reciprocating anion binding site model. The conversion of the transport system from the neutral to the alkaline state is related to deprotonation of a positively charged ionic strength- and substrate-sensitive group. In the absence of substrate ions ([ClO] = 0) the group has a pK of approximately 9.4 at constant high ionic strength (equivalent to approximately 150 mM KCl) and a pK of approximately 8.7 at approximately zero ionic strength. The alkaline ping-pong system (examined at constant high ionic strength) demonstrates outward recruitment of the binding sites with an asymmetry factor of approximately 0.2, as compared with the inward recruitment of the transport system at neutral pHO with an asymmetry factor of approximately 10. The intrinsic half-saturation constant for chloride binding, with [Cli] = [Clo], increased from approximately 30 mM at neutral to approximately 110 mM at alkaline pHO. The maximal transport rate was a factor of approximately 1.7 higher at alkaline pHO. This increase explains the stimulation of anion transport, the "modifier hump," observed at alkaline pHO. The translocation of anions at alkaline pHO was inhibited by deprotonation of another substrate-sensitive group with an intrinsic pK of approximately 11.3. This group together with the group with a pK of approximately 9.4 appear to form the essential part of the exofacial anion binding site. The effect of extracellular iodide inhibition on chloride transport as a function of pHO could, moreover, be simulated if three extracellular iodide binding constants were included in the model: namely, a competitive intrinsic iodide binding constant of approximately 1 mM in the neutral state, a self-inhibitor binding constant of approximately 120 mM in the neutral state, and a competitive intrinsic binding constant of approximately 38 mM in the alkaline state.

scholarly journals The STAS domain of mammalian SLC26A5 prestin harbours an anion-binding site

2016 ◽  
Vol 473 (4) ◽  
pp. 365-370 ◽  
Author(s):  
Graziano Lolli ◽  
Elisa Pasqualetto ◽  
Elisa Costanzi ◽  
Greta Bonetto ◽  
Roberto Battistutta
Keyword(s):  
Binding Site ◽  
Anion Transport ◽  
Anion Binding ◽  
Stas Domain

The STAS domain of mammalian prestin harbours an anion-binding site absent from non-mammalian homologues. This is correlated to different prestin functions, full anion transport in non-mammals and incomplete transport coupled to electromotility and a mechanically amplified hearing process in mammals.

Tuning of Electronic Properties in Conducting Polymers

2001 ◽  
Vol 66 (8) ◽  
pp. 1208-1218 ◽  
Author(s):  
Guofeng Li ◽  
Mira Josowicz ◽  
Jiří Janata
Keyword(s):  
Hydrogen Bonding ◽  
Binding Site ◽  
Binding Sites ◽  
Polymer Chains ◽  
Electronic Transitions ◽  
Weakly Bound ◽  
Ordered Structures ◽  
Doped Polymer ◽  
Positively Charged ◽  
Repeated Cycling

Structural and electronic transitions in poly(thiophenyleneiminophenylene), usually referred to as poly(phenylenesulfidephenyleneamine) (PPSA) upon electrochemical doping with LiClO4 have been investigated. The unusual electrochemical behavior of PPSA indicates that the dopant anions are bound in two energetically different sites. In the so-called "binding site", the ClO4- anion is Coulombically attracted to the positively charged S or N sites on one chain and simultaneously hydrogen-bonded with the N-H group on a neighboring polymer chain. This strong interaction causes a re-organization of the polymer chains, resulting in the formation of a networked structure linked together by these ClO4- Coulombic/hydrogen bonding "bridges". However, in the "non-binding site", the ClO4- anion is very weakly bound, involves only the electrostatic interaction and can be reversibly exchanged when the doped polymer is reduced. In the repeated cycling, the continuous and alternating influx and expulsion of ClO4- ions serves as a self-organizing process for such networked structures, giving rise to a diminishing number of available "non-binding" sites. The occurrence of these ordered structures has a major impact on the electrochemical activity and the morphology of the doped polymer. Also due to stabilization of the dopant ions, the doped polymer can be kept in a stable and desirable oxidation state, thus both work function and conductivity of the polymer can be electrochemically controlled.

scholarly journals Deoxygenation-induced cation fluxes in sickle cells: II. Inhibition by stilbene disulfonates

Blood ◽  
1990 ◽  
Vol 76 (1) ◽  
pp. 212-220 ◽  
Author(s):  
CH Joiner
Keyword(s):  
Binding Site ◽  
Anion Exchange ◽  
Anion Exchanger ◽  
Drug Exposure ◽  
External Surface ◽  
Anion Transport ◽  
Sickle Cells ◽  
Transport Inhibitor ◽  
Cation Permeability

Deoxygenation-induced cation movements in sickle cells were inhibited 80% to 85% by the anion transport inhibitor, 4,4′-diisothiocyano- 2,2′disulfostilbene (DIDS). Morphologic sickling was not altered by DIDS treatment, demonstrating that morphologic sickling was not sufficient to produce cation leaks in sickle cells. DIDS inhibition of deoxygenation-induced cation flux was not affected when l- replaced Cl- , indicating that conductive anion movements did not limit cation flux in deoxygenated cells treated with DIDS. Inhibition was irreversible after preincubation with DIDS at 37 degrees C for 20 minutes, and was not affected by the oxygenation state of cells at the time of drug exposure. Sulfate self-exchange was inhibited at lower DIDS concentrations than was deoxygenation-induced flux. Incubation of cells with DIDS at 4 degrees C produced progressive blockade of sulfate exchange, but did not alter deoxygenation-induced cation fluxes. Other stilbene disulfonates, including compounds incapable of covalent reactions, also inhibited deoxygenation-induced cation movements, although several other inhibitors of anion exchange did not. Dissociation of the inhibition of anion exchange and deoxygenation- induced cation flux indicates that the DIDS effect on deoxygenation- induced cation movements does not involve the well-characterized stilbene binding site of the anion exchanger. These data provide evidence for a membrane constituent on the external surface of oxygenated sickle cells capable of interacting with DIDS to prevent the increase in cation permeability associated with sickling.

The red cell band 3 protein: its role in anion transport

1982 ◽  
Vol 299 (1097) ◽  
pp. 497-507 ◽  
Keyword(s):  
Binding Sites ◽  
Band 3 ◽  
Anion Transport ◽  
Anion Binding ◽  
Hydrophobic Residues ◽  
Ping Pong ◽  
Hydrophilic Residues ◽  
Aqueous Core ◽  
Positively Charged

Studies of anion transport across the red blood cell membrane fall generally into two categories: (1) those concerned with the operational characterization of the transport system, largely by kinetic analysis and inhibitor studies; and (2) those concerned with the structure of band 3, a transmembrane peptide identified as the transport protein. The kinetics are consistent with a ping-pong model in which positively charged anion-binding sites can alternate between exposure to the inside and outside compartments but can only shift one position to the other when occupied by an anion. The structural studies on band 3 indicate that only 60 % of the peptide is essential for transport. That particular portion is in the form of a dimer consisting of an assembly of membrane-crossing strands (each monomer appears to cross at least five times). The assembly presents its hydrophobic residues toward the interior of the bilayer, but its hydrophilic residues provide an aqueous core. The transport involves a small conformational change in which an anion-binding site (involving positively charged residues) can alternate between positions that are topologically in and topologically out.

scholarly journals Mouse Bestrophin-2 Is a Bona fide Cl− Channel

2004 ◽  
Vol 123 (4) ◽  
pp. 327-340 ◽  
Author(s):  
Zhiqiang Qu ◽  
Rodolphe Fischmeister ◽  
Criss Hartzell
Keyword(s):  
Binding Site ◽  
Cell Lines ◽  
Electrostatic Interactions ◽  
Anion Binding ◽  
Wild Type ◽  
Cl Channel ◽  
Mammalian Cell Lines ◽  
Conduction Pathway ◽  
Bona Fide ◽  
Cl Conductance

Bestrophins have recently been proposed to comprise a new family of Cl− channels. Our goal was to test whether mouse bestrophin-2 (mBest2) is a bona fide Cl− channel. We expressed mBest2 in three different mammalian cell lines. mBest2 was trafficked to the plasma membrane as shown by biotinylation and immunoprecipitation, and induced a Ca2+-activated Cl− current in all three cell lines (EC50 for Ca2+ = 230 nM). The permeability sequence was SCN−: I−: Br−: Cl−: F− (8.2: 1.9: 1.4: 1: 0.5). Although SCN− was highly permeant, its conductance was ∼10% that of Cl− and SCN− blocked Cl− conductance (IC50 = 12 mM). Therefore, SCN− entered the pore more easily than Cl−, but bound more tightly than Cl−. Mutations in S79 altered the relative permeability and conductance for SCN− as expected if S79 contributed to an anion binding site in the channel. PSCN/PCl = 8.2 ± 1.3 for wild-type and 3.9 ± 0.4 for S79C. GSCN/GCl = 0.14 ± 0.03 for wild-type and 0.94 ± 0.04 for S79C. In the S79 mutants, SCN− did not block Cl− conductance. This suggested that the S79C mutation altered the affinity of an anion binding site for SCN−. Additional evidence that S79 was located in the conduction pathway was provided by the finding that modification of the sulfhydryl group in S79C with MTSET+ or MTSES− increased conductance significantly. Because the effect of positively and negatively charged MTS reagents was similar, electrostatic interactions between the permeant anion and the channel at this residue were probably not critical in anion selectivity. These data provide strong evidence that mBest2 forms part of the novel Cl− conduction pathway in mBest2-transfected cells and that S79 plays an important role in anion binding in the pore of the channel.

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