Anion binding to ubiquitin and its relevance to the Hofmeister effects.
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ABSTRACT:
SUBMITTER: Yao W
PROVIDER: S-EPMC8178748 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:For over 120 years it has been appreciated that certain salts (kosmotropes) cause the precipitation of proteins, while others (chaotropes) increase their solubility. The cause of this "Hofmeister effect" is still unclear, especially with the original concept that kosmotropic anions "make" water structure and chaotropes "break" it being countered by recent studies suggesting otherwise. Here, we present the first direct evidence that chaotropic anions have an affinity for hydrophobic concavity and that it is competition between a convex hydrophobe and the anion for a binding site that leads to the apparent weakening of the hydrophobic effect by chaotropes. In combination, these results suggest that chaotropes primarily induce protein solubilization by direct binding to concavity in the molten globule state of a protein.
| S-EPMC3098002 | biostudies-literature
Project description:The (1)H?NMR spectroscopic analysis of the binding of the ClO4(-) anion to the hydrophobic, concave binding site of a deep-cavity cavitand is presented. The strength of association between the host and the ClO4(-) anion is controlled by both the nature and concentration of co-salts in a manner that follows the Hofmeister series. A model that partitions this trend into the competitive binding of the co-salt anion to the hydrophobic pocket of the host and counterion binding to its external carboxylate groups successfully accounts for the observed changes in ClO4(-) affinity.
| S-EPMC4214138 | biostudies-literature
Project description:ᅟ: Physical gelation behaviors of a series of D-gluconic acetal-based derivatives bearing fatty alkyl amine moieties have been investigated. One of these molecules exhibits excellent gelation behaviors in water, and the resultant hydrogels are found to display self-healing properties. Interestingly, the elasticity and strength of the resulting gel can be tuned by the addition of different kinds of Hofmeister salts. The gel formation mechanism was proposed based on the analysis of FT-IR,1HNMR, and XRD, indicating that the main driving force for the self-assembly was the π-π stacking of the benzene rings in the aqueous solution system. Overall, our research provides an efficient approach for facilely tuning the properties of the D-gluconic acetal-based hydrogel. ᅟ.
| S-EPMC6321834 | biostudies-literature
Project description:In this communication, a new approach to enhancing the efficacy of liquid-liquid anion exchange is demonstrated. It involves the concurrent use of appropriately chosen hydrogen-bond-donating (HBD) anion receptors in combination with a traditional quaternary ammonium extractant. The fluorinated calixpyrroles 1 and 2 and the tetraamide macrocycle 4 were found to be particularly effective receptors. Specifically, their use allowed the extraction of sulfate by tricaprylmethylammonium nitrate to be effected in the presence of excess nitrate. As such, the present work provides a rare demonstration of overcoming the Hofmeister bias in a competitive environment and the first to the authors' knowledge wherein this difficult-to-achieve objective is attained using a neutral HBD-based anion binding agent under conditions of solvent extraction.
| S-EPMC2650011 | biostudies-literature
Project description:Quantitative interpretation and prediction of Hofmeister ion effects on protein processes, including folding and crystallization, have been elusive goals of a century of research. Here, a quantitative thermodynamic analysis, developed to treat noncoulombic interactions of solutes with biopolymer surface and recently extended to analyze the effects of Hofmeister salts on the surface tension of water, is applied to literature solubility data for small hydrocarbons and model peptides. This analysis allows us to obtain a minimum estimate of the hydration b1 (H2O A(-2)), of hydrocarbon surface and partition coefficients Kp, characterizing the distribution of salts and salt ions between this hydration water and bulk water. Assuming that Na+ and SO4(2-) ions of Na2SO4 (the salt giving the largest reduction in hydrocarbon solubility as well as the largest increase in surface tension) are fully excluded from the hydration water at hydrocarbon surface, we obtain the same b1 as for air-water surface (approximately 0.18 H2O A(-2)). Rank orders of cation and anion partition coefficients for nonpolar surface follow the Hofmeister series for protein processes, but are strongly offset for cations in the direction of exclusion (preferential hydration). By applying a coarse-grained decomposition of water accessible surface area (ASA) into nonpolar, polar amide, and other polar surface and the same hydration b1 to interpret peptide solubility increments, we determine salt partition coefficients for amide surface. These partition coefficients are separated into single-ion contributions based on the observation that both Cl- and Na+ (also K+) occupy neutral positions in the middle of the anion and cation Hofmeister series for protein folding. Independent of this assignment, we find that all cations investigated are strongly accumulated at amide surface while most anions are excluded. Cation and anion effects are independent and additive, allowing successful prediction of Hofmeister salt effects on micelle formation and other processes from structural information (ASA).
| S-EPMC2756543 | biostudies-literature
Project description:Hofmeister effects have been recognized as important as Mendel's work was to genetics while remain largely controversial, especially for the mechanistic aspects. Here we demonstrated that complex colloids in electrolyte solutions show resembling aggregation kinetics as model colloid, and then quantitatively evaluated the resulting Hofmeister effects. Mechanism for the aggregation of complex colloids has been proposed that is closely associated with the charges of their constituents; despite that, electrostatic interactions play a minor role while polarization effect is evidenced to be the driving force for the aggregation processes. Polarization effect is further ascribed to arouse the resulting Hofmeister effects, which is supported by the fine correlation of activation energies vs. polarizability data of different alkali ions and the calculations of dipole moments for minerals with different charges and adsorbed alkali ions. Because of neglecting polarization effect, the prevailing DLVO theory is not sufficient to describe Hofmeister effects that are ubiquitous in nature. We speculate that polarization effect should also be responsible for Hofmeister effects of other charged systems such as proteins and membranes.
| S-EPMC4511582 | biostudies-literature
Project description:Host-mediated liquid-liquid extraction is a convenient method for the separation of inorganic salts. However, selective extraction of an anion, regardless of its hydrophilicity or lipophilicity as qualitatively described by its place in the Hofmeister series, remains challenging. Herein we report the complete disruption of the Hofmeister-based ordering of anions in host-mediated extraction by a rigidified tweezer-type receptor possessing remarkably strong anion-binding affinity under the conditions examined. Experiments introduce a convenient new method for determination of anion binding using phosphorus inductively coupled plasma mass spectrometry (ICP-MS) to measure extraction of tetra-n-butylphosphonium (TBP+) salts from water into nitrobenzene, specifically examining the disrupting effect of the added arylethynyl bisurea anion receptor. In the absence of the receptor, the salt partitioning follows the expected Hofmeister-type ordering favoring the larger, less hydrated anions; the analysis yields the value -24 kJ mol-1 for the standard Gibbs energy of partitioning of TBP+ cation from water into nitrobenzene at 25 °C. Selectivity is markedly changed by the addition of receptor to the nitrobenzene and is concentration dependent, giving rise to three selectivity regimes. We then used SXLSQI liquid-liquid equilibrium analysis software developed at Oak Ridge National Laboratory to fit host-mediated extraction equilibria for TBP+ salts of Cl-, Br-, I-, and NO3- to the distribution data. While the reverse-Hofmeister 1 : 1 binding of the anions by the receptor effectively cancels the Hofmeister selectivity of the TBPX partitioning into nitrobenzene, formation of unexpected 2 : 1 receptor : anion complexes favoring Cl- and Br- dominates the selectivity at elevated receptor concentrations, producing the unusual order Br- > Cl- > NO3- > I- in anion distribution wherein a middle member of the series is selected and the most lipophilic anion is disfavored. Density functional theory calculations confirmed the likelihood of forming 2 : 1 complexes, where Cl- and Br- are encapsulated by two receptors adopting energetically competitive single or double helix structures. The calculations explain the rare non-Hofmeister preference for Br-. This example shows that anion receptors can be used to control the selectivity and efficiency of salt extraction regardless of the position of the anion in the Hofmeister series.
| S-EPMC10988605 | biostudies-literature
Project description:This paper uses the binding pocket of human carbonic anhydrase II (HCAII, EC 4.2.1.1) as a tool to examine the properties of Hofmeister anions that determine (i) where, and how strongly, they associate with concavities on the surfaces of proteins and (ii) how, upon binding, they alter the structure of water within those concavities. Results from X-ray crystallography and isothermal titration calorimetry show that most anions associate with the binding pocket of HCAII by forming inner-sphere ion pairs with the Zn(2+) cofactor. In these ion pairs, the free energy of anion-Zn(2+) association is inversely proportional to the free energetic cost of anion dehydration; this relationship is consistent with the mechanism of ion pair formation suggested by the "law of matching water affinities". Iodide and bromide anions also associate with a hydrophobic declivity in the wall of the binding pocket. Molecular dynamics simulations suggest that anions, upon associating with Zn(2+), trigger rearrangements of water that extend up to 8 Å away from their surfaces. These findings expand the range of interactions previously thought to occur between ions and proteins by suggesting that (i) weakly hydrated anions can bind complementarily shaped hydrophobic declivities, and that (ii) ion-induced rearrangements of water within protein concavities can (in contrast with similar rearrangements in bulk water) extend well beyond the first hydration shells of the ions that trigger them. This study paints a picture of Hofmeister anions as a set of structurally varied ligands that differ in size, shape, and affinity for water and, thus, in their ability to bind to—and to alter the charge and hydration structure of—polar, nonpolar, and topographically complex concavities on the surfaces of proteins.
| S-EPMC6554743 | biostudies-literature
Project description:The molecular conformation of proteins is sensitive to the nature of the aqueous environment. In particular, the presence of ions can stabilize or destabilize (denature) protein secondary structure. The underlying mechanisms of these actions are still not fully understood. Here, we combine circular dichroism (CD), single-molecule Förster resonance energy transfer, and atomistic computer simulations to elucidate salt-specific effects on the structure of three peptides with large ?-helical propensity. CD indicates a complex ion-specific destabilization of the ?-helix that can be rationalized by using a single salt-free computer simulation in combination with the recently introduced scheme of ion-partitioning between nonpolar and polar peptide surfaces. Simulations including salt provide a molecular underpinning of this partitioning concept. Furthermore, our single-molecule Förster resonance energy transfer measurements reveal highly compressed peptide conformations in molar concentrations of NaClO(4) in contrast to strong swelling in the presence of GdmCl. The compacted states observed in the presence of NaClO(4) originate from a tight ion-backbone network that leads to a highly heterogeneous secondary structure distribution and an overall lower ?-helical content that would be estimated from CD. Thus, NaClO(4) denatures by inducing a molten globule-like structure that seems completely off-pathway between a fully folded helix and a coil state.
| S-EPMC3283803 | biostudies-other
Project description:The ferric binding protein, FbpA, has been demonstrated to facilitate the transport of naked Fe3+ across the periplasmic space of several Gram-negative bacteria. The sequestration of iron by FbpA is facilitated by the presence of a synergistic anion, such as phosphate or sulfate. Here we report the sequestration of Fe3+ by FbpA in the presence of sulfate, at an assumed periplasmic pH of 6.5 to form FeFbpA-SO4 with K'(eff) = 1.7 x 10(16) M(-1) (at 20 degrees C, 50 mM MES, 200 mM KCl). The iron affinity of the FeFbpA-SO4 protein assembly is 2 orders of magnitude lower than when bound with phosphate and is the lowest of any of the FeFbpA-X assemblies yet reported. Iron reduction at the cytosolic membrane receptor may be an essential aspect of the periplasmic iron-transport process, and with an E(1/2) of -158 mV (NHE), FeFbpA-SO4 is the most easily reduced of all FeFbpA-X assemblies yet studied. The variation of FeFbpA-X assembly stability (K'(eff)) and ease of reduction (E(1/2)) with differing synergistic anions X(n-) are correlated over a range of 14 kJ, suggesting that the variations in redox potentials are due to stabilization of Fe3+ in FeFbpA-X by X(n-). Anion promiscuity of FbpA in the diverse composition of the periplasmic space is illustrated by the ex vivo exchange kinetics of FeFbpA-SO4 with phosphate and arsenate, where first-order kinetics with respect to FeFbpA-SO4 (k = 30 s(-1)) are observed at pH 6.5, independent of entering anion concentration and identity. Anion lability and influence on the iron affinity and reduction potential for FeFbpA-X support the hypothesis that synergistic anion exchange may be an important regulator in iron delivery to the cytosol. This structural and thermodynamic analysis of anion binding in FeFbpA-X provides additional insight into anion promiscuity and importance.
| S-EPMC3674819 | biostudies-literature