scholarly journals Selective anion transport mediated by strap-extended calixpyrroles

2020 ◽  
Vol 24 (01n03) ◽  
pp. 473-479 ◽  
Author(s):  
Harriet J. Clarke ◽  
Xin Wu ◽  
Mark E. Light ◽  
Philip A. Gale
Keyword(s):  
Fatty Acids ◽  
Chloride Transport ◽  
Anion Transport ◽  
Anion Binding ◽  
Anion Receptors ◽  
Future Design ◽  
Anion Transporters ◽  
Head Groups ◽  
Proton Leakage ◽  
Autophagy Inhibition

Synthetic anion receptors that facilitate transmembrane chloride transport are of interest as potential therapeutic agents for cancer and cystic fibrosis. Transporters selective for chloride over protons are desired for therapeutic applications to avoid autophagy inhibition and cytotoxicity. Examples of such compounds are rare because the majority of anion transporters can interact with the carboxylate head groups of fatty acids leading to proton leakage. In this paper, we report the synthesis, anion binding and transmembrane anion transport properties of two novel bis-triazole-functionalized calixpyrroles with extended straps, and compare them to previously reported shorter-strap analogues known to exhibit high Cl [Formula: see text] H[Formula: see text] selectivity. We demonstrate improved chloride transport activities of the strap-extended compounds that likely benefit from increased lipophilicity, and reduced Cl [Formula: see text] H[Formula: see text] selectivity due to the larger anion binding cavities facilitating interaction with fatty acids. The results are instructive for future design of ideal anion transporters with potent activity and high selectivity against proton leakage.

scholarly journals Investigating the Influence of Steric Hindrance on Selective Anion Transport

Molecules ◽  
2019 ◽  
Vol 24 (7) ◽  
pp. 1278 ◽  
Author(s):  
Laura Jowett ◽  
Angela Ricci ◽  
Xin Wu ◽  
Ethan Howe ◽  
Philip Gale
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Steric Hindrance ◽  
Chloride Transport ◽  
Anion Transport ◽  
Anion Binding ◽  
Chloride Binding ◽  
Anion Receptors ◽  
Flip Flop ◽  
Anion Transporters

A series of symmetrical and unsymmetrical alkyl tren based tris-thiourea anion transporters were synthesised and their anion binding and transport properties studied. Overall, increasing the steric bulk of the substituents resulted in improved chloride binding and transport abilities. Including a macrocycle in the scaffold enhanced the selectivity of chloride transport in the presence of fatty acids, by reducing the undesired H+ flux facilitated by fatty acid flip-flop. This study demonstrates the benefit of including enforced steric hindrance and encapsulation in the design of more selective anion receptors.

scholarly journals Transmembrane Fluoride Transport by a Cyclic Azapeptide With Two β-Turns

2021 ◽  
Vol 8 ◽  
Author(s):  
Zhixing Zhao ◽  
Miaomiao Zhang ◽  
Bailing Tang ◽  
Peimin Weng ◽  
Yueyang Zhang ◽  
...  
Keyword(s):  
Chloride Transport ◽  
Anion Transport ◽  
Bacterial Survival ◽  
Transport Activity ◽  
Selective Electrode ◽  
Design And Synthesis ◽  
Anion Transporters ◽  
Host Compound ◽  
Anion Transport Activity ◽  
Fluoride Ion Selective Electrode

Diverse classes of anion transporters have been developed, most of which focus on the transmembrane chloride transport due to its significance in living systems. Fluoride transport has, to some extent, been overlooked despite the importance of fluoride channels in bacterial survival. Here, we report the design and synthesis of a cyclic azapeptide (a peptide-based N-amidothiourea, 1), as a transporter for fluoride transportation through a confined cavity that encapsulates fluoride, together with acyclic control compounds, the analogs 2 and 3. Cyclic receptor 1 exhibits more stable β-turn structures than the control compounds 2 and 3 and affords a confined cavity containing multiple inner –NH protons that serve as hydrogen bond donors to bind anions. It is noteworthy that the cyclic receptor 1 shows the capacity to selectively transport fluoride across a lipid bilayer on the basis of the osmotic and fluoride ion-selective electrode (ISE) assays, during which an electrogenic anion transport mechanism is found operative, whereas no transmembrane transport activity was found with 2 and 3, despite the fact that 2 and 3 are also able to bind fluoride via the thiourea moieties. These results demonstrate that the encapsulation of an anionic guest within a cyclic host compound is key to enhancing the anion transport activity and selectivity.

scholarly journals Tetrapodal Anion Transporters

Molecules ◽  
2020 ◽  
Vol 25 (21) ◽  
pp. 5179
Author(s):  
Alexander M. Gilchrist ◽  
Lijun Chen ◽  
Xin Wu ◽  
William Lewis ◽  
Ethan N.W. Howe ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Side Effect ◽  
Proton Transport ◽  
High Selectivity ◽  
Chloride Transport ◽  
Anion Transporters ◽  
Selective Interaction

Synthetic anion transporters that facilitate chloride transport are promising candidates for channelopathy treatments. However, most anion transporters exhibit an undesired side effect of facilitating proton transport via interacting with fatty acids present in the membrane. To address the limitation, we here report the use of a new tetrapodal scaffold to maximize the selective interaction with spherical chloride over binding the carboxylate headgroup of fatty acids. One of the new transporters demonstrated a high selectivity for chloride uniport over fatty acid-induced proton transport while being >10 times more active in chloride uniport than strapped calixpyrroles that were previously the only class of compounds known to possess similar selectivity properties.

scholarly journals Carbazole-Based Colorimetric Anion Sensors

Molecules ◽  
2021 ◽  
Vol 26 (11) ◽  
pp. 3205
Author(s):  
Krystyna Maslowska-Jarzyna ◽  
Maria L. Korczak ◽  
Jakub A. Wagner ◽  
Michał J. Chmielewski
Keyword(s):  
Hydrogen Bond ◽  
Visible Region ◽  
Building Blocks ◽  
Anion Transport ◽  
Anion Binding ◽  
Anion Receptors ◽  
Binding Studies ◽  
Anion Sensor ◽  
Anion Sensors ◽  
Anion Interaction

Owing to their strong carbazole chromophore and fluorophore, as well as to their powerful and convergent hydrogen bond donors, 1,8-diaminocarbazoles are amongst the most attractive and synthetically versatile building blocks for the construction of anion receptors, sensors, and transporters. Aiming to develop carbazole-based colorimetric anion sensors, herein we describe the synthesis of 1,8-diaminocarbazoles substituted with strongly electron-withdrawing substituents, i.e., 3,6-dicyano and 3,6-dinitro. Both of these precursors were subsequently converted into model diamide receptors. Anion binding studies revealed that the new receptors exhibited significantly enhanced anion affinities, but also significantly increased acidities. We also found that rear substitution of 1,8-diamidocarbazole with two nitro groups shifted its absorption spectrum into the visible region and converted the receptor into a colorimetric anion sensor. The new sensor displayed vivid color and fluorescence changes upon addition of basic anions in wet dimethyl sulfoxide, but it was poorly selective; because of its enhanced acidity, the dominant receptor-anion interaction for most anions was proton transfer and, accordingly, similar changes in color were observed for all basic anions. The highly acidic and strongly binding receptors developed in this study may be applicable in organocatalysis or in pH-switchable anion transport through lipophilic membranes.

New Polydentate Macrocyclic Ligands of Hybrid Amine-Imine and Amide-Imine Types as Artificial Anion Receptors. Synthesis and Study of Anion Binding.

ChemInform ◽  
2005 ◽  
Vol 36 (52) ◽  
Author(s):  
E. A. Katayev ◽  
G. D. Pantos ◽  
V. M. Lynch ◽  
J. L. Sessler ◽  
M. D. Reshetova ◽  
...  
Keyword(s):  
Macrocyclic Ligands ◽  
Anion Binding ◽  
Anion Receptors

scholarly journals Fatty Acid Fueled Transmembrane Chloride Transport

2019 ◽  
Author(s):  
Ethan N.W. Howe ◽  
Philip Gale
Keyword(s):  
Fatty Acids ◽  
Fatty Acid ◽  
Lipid Bilayer ◽  
Chloride Transport ◽  
Bilayer Membrane ◽  
Lipid Bilayer Membrane ◽  
Ph Gradient ◽  
Pumping System ◽  
Membrane Addition

We report an example of the use of fatty acids to drive chloride transport by creating a pH gradient across a vesicular lipid bilayer membrane. Addition of an unselective squaramide-based chloride transporter (which transports both H<sup>+</sup>and Cl<sup>-</sup>) facilitates the transport of HCl from the vesicle (driven by the pH gradient) so creating a chloride gradient. Addition of further aliquots of fatty acid ‘fuel’ can initiate further transport of chloride out of the vesicle by re-establishing the pH gradient. This is an example of a prototypical chloride pumping system.

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 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 Characterization of Guided Entry of Tail-Anchored Proteins 3 Homologues in Mycobacterium tuberculosis

2019 ◽  
Vol 201 (14) ◽  
Author(s):  
Kuan Hu ◽  
Ashley T. Jordan ◽  
Susan Zhang ◽  
Avantika Dhabaria ◽  
Amanda Kovach ◽  
...  
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Structure Prediction ◽  
Bacterial Species ◽  
Normal Growth ◽  
Anion Transport ◽  
Content Type ◽  
Reading Frame ◽  
Anion Transporters ◽  
Anion Transporter

ABSTRACT We characterized an operon in Mycobacterium tuberculosis, Rv3679-Rv3680, in which each open reading frame is annotated to encode “anion transporter ATPase” homologues. Using structure prediction modeling, we found that Rv3679 and Rv3680 more closely resemble the guided entry of tail-anchored proteins 3 (Get3) chaperone in eukaryotes. Get3 delivers proteins into the membranes of the endoplasmic reticulum and is essential for the normal growth and physiology of some eukaryotes. We sought to characterize the structures of Rv3679 and Rv3680 and test if they have a role in M. tuberculosis pathogenesis. We solved crystal structures of the nucleotide-bound Rv3679-Rv3680 complex at 2.5 to 3.2 Å and show that while it has some similarities to Get3 and ArsA, there are notable differences, including that these proteins are unlikely to be involved in anion transport. Deletion of both genes did not reveal any conspicuous growth defects in vitro or in mice. Collectively, we identified a new class of proteins in bacteria with similarity to Get3 complexes, the functions of which remain to be determined. IMPORTANCE Numerous bacterial species encode proteins predicted to have similarity with Get3- and ArsA-type anion transporters. Our studies provide evidence that these proteins, which we named BagA and BagB, are unlikely to be involved in anion transport. In addition, BagA and BagB are conserved in all mycobacterial species, including the causative agent of leprosy, which has a highly decayed genome. This conservation suggests that BagAB constitutes a part of the core mycobacterial genome and is needed for some yet-to-be-determined part of the life cycle of these organisms.

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