Electrostatic Interactions In Solution Research Articles

Direct mass spectrometric determination of the stoichiometry and binding affinity of the complexes between nucleocapsid protein and RNA stem-loop hairpins of the HIV-1 Psi-recognition element.

The formation of noncovalent complexes between the HIV-1 nucleocapsid protein p7 (NC) and RNA hairpins SL2-SL4 of the Psi-recognition element was investigated by direct infusion electrospray ionization-Fourier transform mass spectrometry (ESI-FTMS). The high resolution afforded by this method provided the unambiguous characterization of the stoichiometry and composition of complexes formed by multiple equilibria in solution. For each hairpin, the formation of a 1:1 complex was found to be the primary binding mode in solutions of intermediate salt content (150 mM ammonium acetate). Binding of multiple units of NC was observed with lower affinity and a maximum stoichiometry matching the limit calculated from the number of nucleotides in the construct and the size of the footprint of NC onto single-stranded nucleic acids, thus implying the defolding of the hairpin three-dimensional (3D) structure. Dissociation constants of 62 +/- 22 nM, 178 +/- 64 nM, and 1.3 +/- 0.5 microM were determined for SL2, SL3-2, and SL4, respectively, which are similar to values obtained by spectroscopic and calorimetric methods with the additional confidence offered by a direct, rather than inferred, knowledge of the binding stoichiometry. Competitive binding experiments carried out in solutions of intermediate ionic strength, which has the effect of weakening the electrostatic interactions in solution, provided a direct way of evaluating the stabilizing contributions of H-bonding and hydrophobic interactions that are more sensitive to the sequence and structural context of the different hairpins. The relative scale of binding affinity obtained in this environment reflects the combination of contributions provided by the different structures of both the tetraloop and the double-stranded stem. The importance of the stem 3D structure in modulating the binding activity was tested by a competitive binding experiment that included the SL3-2 RNA construct, a DNA analogue of SL3 (SL3(DNA)), and a DNA analogue in which all four loop bases were replaced with abasic nucleotides (SL3(abasic)). NC was found to bind the A-type double-stranded stem of SL3-2 RNA at least 30 times more tightly than the B-type helical structure of SL3(DNA). Eliminating the stabilization provided by the interactions with the tetraloop bases made the binding of SL3(abasic) approximately 50 times weaker than that of SL3(DNA).

Counterion penetration and effective electrostatic interactions in solutions of polyelectrolyte stars and microgels.

Counterion distributions and effective electrostatic interactions between spherical macroions in polyelectrolyte solutions are calculated via second-order perturbation (linear response) theory. By modeling the macroions as continuous charge distributions that are permeable to counterions, analytical expressions are obtained for counterion profiles and effective pair interactions in solutions of star-branched and microgel macroions. The counterions are found to penetrate stars more easily than microgels, with important implications for screening of bare macroion interactions. The effective pair interactions are Yukawa in form for separated macroions, but are softly repulsive and bounded for overlapping macroions. A one-body volume energy, which depends on the average macroion concentration, emerges naturally in the theory and contributes to the total free energy.

Scattering properties of multicomponent polymer solutions: polyelectrolytes, homopolymer mixtures and diblock copolymer

AbstractThis article reviews the understanding of static and dynamic scattering properties of multicomponent polymer systems in solution achieved during the past decade. We shall describe particularly ternary polymer systems which include polyelectrolyte solutions (polyion/counter‐ions/water), mixture of homopolymers (A and B)/solvent and the case of diblock copolymer (A‐B, linear or cyclic) solutions. The purpose of this paper is not an extensive survey of theoretical and experimental results obtained on the scattering behavior of these systems but rather an updating of recent results. For polyelectrolyte systems we shall focus, by means of scattering techniques, on the conformation of the polyelectrolyte chain and on the structure of the system induced by the dominant electrostatic interactions in solution involving polyions, counter‐ions and solvent. As for the mixture of homopolymers in solution and diblock copolymer/solvent systems, we shall mainly discuss their dynamic behavior and show that using linear response theory and the Random Phase Approximation (RPA), two relaxation modes describe the autocorrelation functions as revealed using dynamic light scattering (DLS) or/and Neutron Spin Echo (NSE) techniques: the first mode characterizes the concentration fluctuations and the second one the composition fluctuations. We shall discuss the scattering properties of these systems on the basis of recent developments with emphasis on possible coiling of the polyelectrolyte chain at low charge density and also how important parameters such as the mobility of the chain (diffusion process) and the interaction parameter (compatibility), which control the dynamics and the thermodynamics in homopolymer mixtures and diblock copolymer systems, could be deduced from scattering experiments.

Simulation of 1-Aminopropanephosphonic Acids with Consideration of Aqueous Solutions

Abstract While solid state structures of aminophosphonic acids are well characterised by X-Ray methods only few informations are available concerning the solution state structures. We have attempted to simulate the structures of acids and corresponding cations and anions in aqueous solutions. It proved to be difficult to describe correctly the electrostatic interactions of solute and solvent by theoretical methods.

Human Erythrocyte Catalase: 2-D Crystal Nucleation and Production of Multiple Crystal Forms

Negatively stained electron microscope images are presented, showing the nucleation of two-dimensional (2-D) crystals of human erythrocyte catalase produced on mica by the negative staining-carbon film technique. Examples of the formation of partially ordered 2-D arrays and more ordered 2-D crystals are shown and the conditions required for the production of large well-ordered 2-D crystals discussed. The structural transformation of one flexuous 2-D paracrystal into a p2 2-D crystal is considered. The crystallographic 2-D image average of this p2 crystal form is presented (lattice parameters a = 9.0 nm, b = 18.6 nm; γ= 90-8°). It is shown that transmission electron microscopy provides the possibility of defining 2-D crystal nucleation, growth of intermediate forms, and low-resolution crystallographic structural analysis of 2-D crystals of human erythrocyte catalase. Comparison of the various electron microscopical negatively stained images with the peptide backbone of the X-ray structure of bovine liver catalase at different tilt and rotation positions correlates with and emphasizes the multiple intermolecular contacts and orientations that can be adopted by human erythrocyte catalase, leading to various 2-D arrays and 2-D crystals. Alignment of the surface groups involved in the protein-protein interactions that occur during 2-D crystal nucleation and crystal growth may ultimately be determined. From this approach, when taken together with detailed consideration of protein-solvent and protein-solute electrostatic interactions in solution, and at the fluid-air interface, it is considered that a more general theory of crystal nucleation and growth may eventually emerge.

Overall and internal protein dynamics in solution studied by the nonselective proton relaxation.

A new algorithm for the analysis of nonselective proton relaxation data in protein solution is presented. T1 and T2 of protein protons in lysozyme and RNase solutions were measured at three resonance frequencies--11, 27 and 90 MHz. In addition we measured water T1 dispersions in lysozyme solutions over the frequency range of 10 kHz--10 MHz on a field-cycling installation. It was found that the correlation function of protein Brownian tumbling as a whole is nonexponential: in addition to a component with the usual correlation time tau t it contained also a component with a correlation time exceeding tau t by approximately an order of magnitude and with a small relative amplitude. The experiment shows that the parameters of the slow component of the tumbling correlation function depend both on the concentration and on the pH of the protein solution. To explain the results obtained one must take into account the interprotein electrostatic interactions in solution. All protein molecules in solution experience electrostatic torques from their neighbors and this gives rise to an anisotropy in the protein Brownian tumbling. The lifetime of this anisotropy is controlled by the translational diffusion of proteins.

Studies of protein–nucleic acid interactions by photon correlation spectroscopy. I. tRNA–BSA interactions at low ionic strength

Photon correlation measurements of tRNA–BSA association in 1 mM sodium cacodylate buffer are reported. In terms of the overall geometry of the reactants (tRNA and BSA) and their aggregates as well as the reaction rate constants, we have confirmed that, in tRNA–BSA solutions, the tRNA–BSA aggregates in the presence of an excess of BSA are twice as big as those in an excess of tRNA. Furthermore, the experimentally estimated association rate constant is two orders of magnitude lower than the one calculated for a diffusion controlled reaction without taking into account electrostatic interactions in solution. Thus, it is important to include long-range repulsive electrostatic interactions which tend to slow down the reaction markedly.

The crystallisation of alkaline‐earth metal oxides from metal chloride melts: Solubility‐temperature phase diagram analyses and preliminary experimental studies

AbstractThe solubility v temperature phase diagrams for magnesium, calcium, strontium and barium oxide solutions, in lithium, sodium and potassium chloride melts and in the alkaline earth metal chloride melts, have been analysed. The solutions in the alkali metal chlorides are pseudo‐binary reciprocal ternary mixtures; the more soluble barium and strontium oxides showed small deviations, calcium oxide showed larger deviations while the extremely sparingly‐soluble magnesium oxide showed extensive deviations from ideality. These deviations were related to electrostatic interactions in solution, that depended in turn on some function of reciprocal solute and solvent caiton radii. The solutions in the alkalineearth metal chlorides are binary mixtures with MO · 4 MCl2 solvate formation. — Some preliminary crystallisation experiments were carried out, by slow cooling of saturated solutions in the metal chloride melts: calcium and strontium oxide crystallisation from lithium chloride melts and barium oxide crystallisation from all three alkali metal chloride melts would be worth further investigation.

Thermodynamics of the interaction of transition metal ions with histamine

The thermodynamic functions of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes with histamine have been determined in a medium of 0·2M KNO 3. The analysis of results shows the bis-histamino Cu(II) complex to be square planar, bis-histamino Co(II) and Ni(II) as octahedral and bis-histamino Zn(II) to have tetrahedral symmetry. A comparison of the thermodynamic functions of these complexes with the corresponding bis-histidino complexes indicates little electrostatic interaction in solution between carboxylic radical in histidine and these metal ions.