Interaction Of Divalent Metal Ions Research Articles

Solid-State NMR Study to Probe the Effects of Divalent Metal Ions (Ca2+ and Mg2+) on the Magnetic Alignment of Polymer-Based Lipid Nanodiscs.

Divalent cations, especially Ca2+ and Mg2+, play a vital role in the function of biomolecules and making them important to be constituents in samples for in vitro biophysical and biochemical characterizations. Although lipid nanodiscs are becoming valuable tools for structural biology studies on membrane proteins and for drug delivery, most types of nanodiscs used in these studies are unstable in the presence of divalent metal ions. To avoid the interaction of divalent metal ions with the belt of the nanodiscs, synthetic polymers have been designed and demonstrated to form stable lipid nanodiscs under such unstable conditions. Such polymer-based nanodiscs have been shown to provide an ideal platform for structural studies using both solid-state and solution NMR spectroscopies because of the near-native cell-membrane environment they provide and the unique magnetic-alignment behavior of large-size nanodiscs. In this study, we report an investigation probing the effects of Ca2+ and Mg2+ ions on the formation of polymer-based lipid nanodiscs and the magnetic-alignment properties using a synthetic polymer, styrene maleimide quaternary ammonium (SMA-QA), and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipids. Phosphorus-31 NMR experiments were used to evaluate the stability of the magnetic-alignment behavior of the nanodiscs for varying concentrations of Ca2+ or Mg2+ at different temperatures. It is remarkable that the interaction of divalent cations with lipid headgroups promotes the stacking up of nanodiscs that results in the enhanced magnetic alignment of nanodiscs. Interestingly, the reported results show that both the temperature and the concentration of divalent metal ions can be optimized to achieve the optimal alignment of nanodiscs in the presence of an applied magnetic field. We expect the reported results to be useful in the design of nanodisc-based nanoparticles for various applications in addition to atomic-resolution structural and dynamics studies using NMR and other biophysical techniques.

Binding thermodynamics of divalent metal ions to several biological buffers

The interactions of divalent metal ions with several normal biological buffers, such as 2-(N-morpholino)ethane sulfonic acid (MES), 3-(N-morpholino)propane sulfonic acid (MOPS), 4-(2-hydroxyethyl)-1-piperazineethane sulfonic acid (HEPES), tris(hydroxymethyl)aminomethane (Tris) and N-[tris(hydroxymethyl)methyl]-2-aminoethanesulfonic acid (TES) have been investigated by using isothermal titration calorimetry (ITC) from the calorimetric perspective. MES at pH 6.0 does not form complexes with Zn2+, Cd2+, Ca2+, Co2+, Mg2+, Mn2+, and Ni2+, and shows imperceptible complexation ability to Cu2+ and Pb2+. MOPS and HEPES at pH 7.4 show no binding affinity to Ca2+, Co2+, Mg2+, Mn2+, and Ni2+, mild binding affinity towards Cu2+ and Pb2+, and weak binding affinity to Zn2+ and Cd2+. The metal complexation abilities of Tris are much stronger than MOPS or HEPES, especially towards Cu2+ and Pb2+. TES shows negligible binding affinity to Zn2+, Cd2+, Ca2+, Co2+, Mg2+, Mn2+, and Ni2+, and a moderate binding affinity towards Cu2+.

Interaction of divalent metal ions with human translocase of inner membrane of mitochondria Tim23

The preprotein translocase of the inner membrane of mitochondria (TIM23 complex) is the main entry gate for proteins of the matrix and the inner membrane. Tim23p, the core component of TIM23 complex, forms the import pore across the inner membrane and exerts a key function in the protein import. However, the interaction of divalent metal ions with Tim23p and the contribution in the interaction of presequence peptide with Tim23p are still unknown. Herein, we investigated the interaction of divalent metal ions with the intermembrane space domain of Tim23p (Tim23IMS) and the interaction of presequence peptides with Tim23IMS in presence of Ca2+ ion by fluorescence spectroscopy in vitro. The static fluorescence quenching indicates the existence of strong binding between divalent metal ions and Tim23IMS. The order of the binding strength is Ca2+, Mg2+, Cu2+, Mn2+, and Co2+ (from strong to weak). Moreover, the interaction of presequence peptides with Tim23IMS is weakened in presence of Ca2+ ion, which implicates that Ca2+ ion may play an important role in the protein import by TIM23 complex.

Interaction of divalent metal ions with the carboxyl-terminal domain of human voltage-gated proton channel Hv1.

The voltage-gated proton channel Hv1 functions as a dimer, in which the intracellular C-terminal domain of the protein is responsible for the dimeric architecture and regulates proton permeability. Although it is well known that divalent metal ions have effect on the proton channel activity, the interaction of divalent metal ions with the channel in detail is not well elucidated. Herein, we investigated the interaction of divalent metal ions with the C-terminal domain of human Hv1 by CD spectra and fluorescence spectroscopy. The divalent metal ions binding induced an obvious conformational change at pH 7 and a pH-sensitive reduction of thermostability in the C-terminal domain. The interactions were further estimated by fluorescence spectroscopy experiments. There are at least two binding sites for divalent metal ions binding to the C-terminal domain of Hv1, either of which is close to His(244) or His(266) residue. The binding of Zn(2+) to the two sites both enhanced the fluorescence of the protein at pH 7, whereas the binding of other divalent metal ions to the two sites all resulted fluorescence quenching. The orders of the strength of divalent metal ions binding to the two sites from strong to weak are both Co(2+), Ca(2+), Ni(2+), Mg(2+), and Mn(2+). The strength of Ca(2+), Co(2+), Mg(2+), Mn(2+) and Ni(2+) binding to the site close to His(244) is stronger than that of these divalent metal ions binding to the site close to His(266).

Interaction of divalent metal ions with human translocase of inner membrane of mitochondria Tim50

The preprotein translocase of the inner membrane of mitochondria (TIM23 complex) is the main entry gate for proteins of the matrix and the inner membrane. Tim50 is a major receptor for transporting the precursor protein across the mitochondrial inner membrane in TIM23 complex. However, the interaction of divalent metal ions with Tim50 and the contribution in the interaction of presequence peptide with Tim50 are still unknown. Herein, we investigated the interaction of divalent metal ions with the intermembrane space domain of Tim50 (Tim50IMS) and the interaction of presequence peptides with Tim50IMS in presence of Ca2+ ion by fluorescence spectroscopy in vitro. The static fluorescence quenching indicates the existence of strong binding between divalent metal ions and Tim50IMS. The order of the binding strength is Ca2+, Mg2+, Cu2+, Mn2+, and Co2+ (from strong to weak). Moreover, the interaction of presequence peptides with Tim50IMS is weakened in presence of Ca2+ ion, which implicates that Ca2+ ion may play an important role in the protein import by TIM23 complex.

Role of large thermal fluctuations and magnesium ions in t-RNA selectivity of the ribosome.

The fidelity of translation selection begins with the base pairing of codon-anticodon complex between the m-RNA and tRNAs. Binding of cognate and near-cognate tRNAs induces 30S subunit of the ribosome to wrap around the ternary complex, EF-Tu(GTP)aa-tRNA. We have proposed that large thermal fluctuations play a crucial role in the selection process. To test this conjecture, we have developed a theoretical technique to determine the probability that the ternary complex, as a result of large thermal fluctuations, forms contacts leading to stabilization of the GTPase activated state. We argue that the configurational searches for such processes are in the tail end of the probability distribution and show that the probability for this event is localized around the most likely configuration. Small variations in the repositioning of cognate relative to near-cognate complexes lead to rate enhancement of the cognate complex. The binding energies of over a dozen unique site-bound magnesium structural motifs are investigated and provide insights into the nature of interaction of divalent metal ions with the ribosome.

Targeting Divalent Metal Ions at the Active Site of the HIV-1 RNase H Domain: NMR Studies on the Interactions of Divalent Metal Ions with RNase H and Its Inhibitors

HIV-1 reverse transcriptase (RT) RNase H (HIV-RH) is a key target of anti-AIDS drugs. Metal-chelating compounds are an important class of chemicals in pharmacological drug discovery, especially in relation to HIV-RT and the highly-related HIV-integrase. The correlation between the metal-chelating properties and enzyme activities of the metal chelators is always of high scientific interest, as an understanding of this may accelerate the rational optimization of this class of inhibitors. Our NMR data show that Mg2+ and Ca2+ bind specifically to the active site of the RNase H domain and two Mg2+ ions sequentially bind one molecule of RNase H. We also demonstrate here, using saturated and unsaturated tricyclic N-hydroxypyridones designed to block the active site, that the primary binding sites and affinities of divalent metal ions are correlated with the structures of the chelating motifs. Chemical shift perturbation studies of protein/metal-ion/compound ternary complexes also indicate that divalent metal ions play important roles for the specific interaction of the compounds with the RNase H active site.

Targeting Divalent Metal Ions at the Active Site of the HIV-1 RNase H Domain: NMR Studies on the Interactions of Divalent Metal Ions with RNase H and Its Inhibitors

Targeting Divalent Metal Ions at the Active Site of the HIV-1 RNase H Domain: NMR Studies on the Interactions of Divalent Metal Ions with RNase H and Its Inhibitors

Specific Interactions of Divalent Metal Ions with a DNA Duplex Containing the d(CA)n/(GT)n Tandem Repeat

Divalent metal ions are essential for maintaining functional states of the DNA molecule. Their participation in DNA structure is modulated by the base sequence and varies depending on the nature of the ion. The present investigation addresses the interaction of Ca2+ ions with a tandem repeat of two CA dinucleotides, (CA)2/(TG)2. The binding of Ca2+ to the repeat is monitored by nuclear magnetic resonance (NMR) spectroscopy using chemical shift mapping. Parallel experiments monitor binding of Mg2+ ions to the repeat as well as binding of each ion to a DNA duplex in which the (CA)2/(TG)2 repeat is eliminated. The results reveal that the direction and the magnitude of chemical shift changes induced by Ca2+ ions in the NMR spectra of the repeat are different from those induced by Mg2+ ions. The differences between the two cations are significantly diminished by the elimination of the (CA)2/(TG)2 repeat. These findings suggest a specific interaction of Ca2+ ions with the (CA)2/(TG)2 motif. The specificity of the interaction resides in the two A-T base pairs of the repeat, and it involves the major groove of the first A-T base pair and both grooves of the second A-T base pair.

Interaction of divalent metal ions with DNA investigated by 23Na NMR relaxation

The interaction between Na-DNA and divalent metal cations (Mg2+, Mn2+, Co2+ and Ni2+) has been investigated by 23Na NMR relaxation. The experimental data have been interpreted in terms of Manning's counterion condensation theory and a two-site exchange for the sodium ions. The experiments showed that Mn2+ affects the polyion surface atmosphere in a different way from the other metal ions. This behaviour may be due to sugar puckering transition of the DNA induced by Mn2+.

Interaction of curcumin with phosphatidylcholine: A spectrofluorometric study.

Curcumin [1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3, 5-dione], the main constituent of the rhizomes of the plant Curcume longa L. (turmeric), is a powerful antioxidant in both enzymatic and nonenzymatic systems. The interactions of curcumin with egg and soy phosphatidylcholine were followed by fluorescence spectroscopy. Curcumin had very weak fluorescence in aqueous system, which was enhanced in apolar environments. Curcumin emitted at 490 nm after being excited at 451 nm in phosphatidylcholine micelles. The equilibrium constants for the interaction of curcumin with egg and soy phosphatidylcholine were (3.26 +/- 0.2) x 10(5) and (2.64 +/- 0.2) x 10(5) M(-1), respectively. From the Scatchard plot of the fluorometric data, it was inferred that one molecule of curcumin could bind six molecules of phosphatidylcholine. The equilibrium constant for the phosphatidylcholine-curcumin interaction decreased with temperature, indicating the amphiphilic nature of curcumin. The DeltaG, DeltaH, and DeltaS values obtained for the interaction of egg phosphatidylcholine-curcumin were -7.8 +/- 0.3 kcal/mol, -9.6 +/- 0.4 kcal/mol, and -6.8 +/- 0.2 cal/mol/K, respectively. The fluorescence anisotropy measurements of curcumin with phosphatidylcholine suggested that the anisotropy of the curcumin molecule did not change in phosphatidylcholine. The interaction of divalent metal ions with phosphatidylcholine-curcumin in comparison with phosphatidylcholine-1-anilino-8-naphathalenesulfonic acid complex suggested the strong binding of curcumin to metal ions.

Voltammetric and spectroscopic investigation of binding in complexes of divalent metal ions with styrene–maleic acid-copolymer and monomeric analogues

The interaction of divalent metal ions with styrene–maleic acid-copolymer (SMA copolymer) has been studied. Polarography, voltammetry on a hanging mercury electrode and UV-VIS spectroscopy were applied to evaluate formation constants for complexation of Cu(II), Zn(II) and Ni(II) ions with the polyelectrolyte SMA copolymer as well as monomeric dicarboxylic acids in aqueous solution. Considering adsorption of the polymer on the Hg electrode the studies show that SMA acts as strong ligand for Cu(II) ions while complexation with Zn(II) is less strong. Voltammetric behavior of Ni(II) in polymer solutions was found to be rather complex. Formation constants of Cu(II) and Zn(II) polymer complexes are considerably greater compared to the corresponding monomeric metal complexes. The results reported point to a strong influence of metal dissolution on the mechanism of deposition of MA copolymers on copper, zinc and nickel electrodes.

Interaction of divalent metal ions with D-aldonic acids in the solid phase-II. Structural information

Complexes formed between d-glucoheptonate, d-galactonate, d-gulonate and d-ribonate, and several metal ions were obtained in the solid state. Specifically: d-glucoheptonates, Be(C7H13O8)2 · 1\\2H2O, Mn(C7H13O8)2 · 2H2O, Co(C7H13O8)2 · 2H2O, Ni(C7H13O8)2 · 2H2O, Cu(C7H13O8)2 · 2H2O, Pb(C7H13O8)2; d-galactonates, Mn(C6H11O7)2 · 2H2O, Co(C6H11O7)2 · 3H2O, Ni(C6H11O7)2 · 3H2O, Cu(C6H11O7)2, Pb(C6H11O7)2; d-gulonates, Co(C6H11O7)2 · H2O, Ni(C6H11O7)2 · 2H2O, Cu(C6H11O7)2 · 2H2O; d-ribonates, Mn(C5H9O6)2, Co(C5H9O6)2 · 2H2O, Ni(C5H9O6)2 · 2H2O, Cu(C5H9O6)2.2H2O and Pb(C5H9O6)2 have been isolated. These metal sugar salts were characterized by elemental analysis, thermogravimetric analysis, magnetic susceptibility measurements, FT–IR, diffuse reflectance and EPR spectroscopies.

Interaction of divalent metal ions with Zn(2+)-glycerophosphocholine cholinephosphodiesterase from ox brain.

The effect of divalent metal ions on the activity of glycerophosphocholine cholinephosphodiesterse from ox brain was examined. Zn(2+)- and Co(2+)-glycerophosphocholine cholinephosphodiesterases were prepared from the exposure of apoenzyme to Zn2+ and Co2+, respectively, and the properties of two metallo-phosphodiesterases were compared to those of native phosphodiesterase. Although two metallo-enzymes were similar in expressing Km value, optimum pH or sensitivity to Cu2+, they differed in the susceptibility to the inhibition by thiocholine or tellurite; while Co(2+)-phosphodiesterase was more sensitive to tellurites, Zn(2+)-phosphodiesterase was more susceptible to inhibition by thiocholine. In addition, Zn(2+)-phosphodiesterase was more thermo-stable than Co2+ enzyme. Separately, when properties of native phosphodiesterase were compared to those of each metallo-phosphodiesterase, native phosphodiesterase was found to be quite similar to Zn(2+)-phosphodiesterase in many respects. Even in thermo-stability, native enzyme resembled Zn(2+)-phosphodiesterase rather than Co(2+)-enzyme. Consistent with this, the stability of native phosphodiesterase was maintained in the presence of Zn2+, but not Co2+, Mn2+ was also as effective as Zn2+ in the stabilization of the enzyme. Noteworthy, the native enzyme was found to be inhibited competitively by Cu2+ with a Ki value of 20 microM, and its inhibitory action was antagonized effectively by Zn2+ or Co2+. Also, choline, another competitive inhibitor of the enzyme, appeared to antagonize the inhibitory action of Cu2+. Taken together, it is suggested that there may be multiple binding sites for divalent metal ions in the molecule of glycerophosphocholine cholinephosphodiesterase.

Interaction of divalent metal ions with d-gluconic acid in the solid phase and aqueous solution

The interaction of d-gluconic acid with Mn II, Co II, Ni II, Cu II, Cd II, Hg II and Pb II has been investigated. Compounds of the type Mn( d-gluconate) 2·3H 2O, Co( d-gluconate) 2·3H 2O, Ni( d-gluconate) 2·3H 2O, Cu( d-gluconate) 2·3H 2O, Cd( d-gluconate) 2, Hg( d-gluconate)OH and Pb( d-gluconate) 2 have been isolated. These metal-sugar salts were characterized by elemental, thermogravimetric analyses and FT-IR, UV-vis absorption, EPR and 13C NMR spectroscopies. In addition, a quantitative study of the equilibria involved in the interaction of this sugar and the above mentioned metal ions in an aqueous medium was carried out by means of potentiometric measurements of the hydrogen ion concentrations at 20°C andμ = 0.100M (NaNO 3). On the basis of spectroscopic studies, possible structures of these complex species were discussed.

Interaction of divalent metal ions with fructose 2,6-bisphosphate and analogs

A study of the interaction of Mg(II), Ca(II), Zn(II), and Cd(II) ions with fructose phosphates like fructose 2,6-bisphosphate, fructose 1,6-bisphosphate, and fructose 6-phosphate has been carried out. In order to perform this study, ionization constants of the ligands are determined from EMF data at 298 K and ionic strength I = 0.1 M in aqueous solution, and the stability constants of the complexes containing a 1:1 ratio of the ligand to the metal have been reported at 298 K.

Fullerates: interaction of divalent metal ions with Langmuir monolayers and multilayers of mono-substituted C60–malonic acid

Stable Langmuir monolayers of C60[C(CO2H)2] are formed on pure water and on solutions containing Ca2+ or Cd2+ ions; catioN–Headgroup interactions result in expanded monolayers and the transfer of Ca2+–fullerene multilayers onto quartz substrates.

Cooperative Interaction of Divalent Metal Ions, Substrate, and Tissue Factor with Factor VIIa

Factor VIIa-tissue factor (TF) complex formation in the presence of EDTA or divalent cations (Me2+) was investigated. The influence of Me2+ on the amidolytic activity of factor VIIa and factor VIIa-TF complex was evaluated using low molecular weight synthetic substrates possessing substituted aminonaphthalenesulfonamides as detecting groups. Factor VIIa expressed low amidolytic activity in the presence of EDTA. In the presence of EDTA and saturating concentrations of TF, the amidolytic activity of factor VIIa was increased approximately 90-fold. Gel electrophoresis and sedimentation velocity studies demonstrated complex formation between factor VIIa and TF in the presence of EDTA. Substrate titration curves obtained at fixed factor VIIa and TF concentrations gave sigmoidal shapes, indicating that substrates influenced factor VIIa amidolytic activity in the presence of TF. In the absence of Me2+, the KD,app of the factor VIIa-TF complex was influenced by substrate structure and varied from 3.9 to 34 nM. All Me2+ used increased the amidolytic activity of factor VIIa approximately 8-fold compared with experiments in the presence of EDTA. The KD,app values for factor VIIa-Ca2+ complex and factor VIIa-Mn2+ complex were independent of substrate and were 270 and 40 microM, respectively. The KD,app for factor VIIa-Mg2+ complex varied from 3 to 12 mM and was substrate structure dependent. The presence of TF had no influence upon the KD,app for the factor VIIa-Ca2+ complex. The amidolytic activity of factor VIIa was enhanced by TF significantly in the presence of Ca2+, and similar results were obtained with Mg2+ and Mn2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Adsorption and coprecipitation of divalent metals with mackinawite (FeS)

The interactions of divalent metal ions with the common metastable sedimentary iron monosulfide mineral mackinawite were investigated in dilute solutions and seawater. The surface affinities of metals whose sulfide phases are more soluble than mackinawite are similar, whereas those metals whose sulfide phases are less soluble than mackinawite exhibit an increasing surface affinity with decreasing solubility. Adsorption of metals from dilute solutions and seawater was the same, within our experimental uncertainty, and not strongly sensitive to temperature. The partition coefficients of metals in mackinawite strongly increase with decreasing metal solubility and are very temperature sensitive. These results are interpreted as indicating that mackinawite is potentially a major temporary sink for many trace metals during early diagenesis in anoxic sediments.

Interaction of divalent metal ions with the NADP+-malic enzyme from maize leaves

The effect of several metal ions on NADP+-malic enzyme (EC 1.1.1.40) purified from Zea mays L. leaves was studied Mg2+, Mn2+, Co2+ and Cd2+ were all active metal cofactors. The malic enzyme from maize has a moderately high intrinsic preference for Mn2+ relative to Mg2+ at pH 7.0 and 8.0 Negative cooperativity detected in the binding of Mg2+ at pH 7.0 and 8.0 and in the binding of Mn2+ at pH 7.0 suggests the existence of at least two binding sites with different affinity. All of the activating metal ions have preference for octahedral coordination geometry and have ionic radii of 0.86–1.09 A. The ions that act as inhibitors are outside this range and/or are incapable of octahedral coordination. Ba2+, Sr2+, Cd2+, Ca2+, Be2+, Ni2+, Cu2+, Zn2+, Co2+, Hg2+ showed mixed-type inhibition. The reciprocal of their K1 values follow the order of their apparence in the Irving-Williams series of stability that derives in part from size effects. It is suggested that the size of the ions may play a partial role in determining the strength of the metal interaction.