Heat and Entropies of Formation of Metal Chelates of Polyamine and Polyaminocarboxylate Ligands.

Wright, D.; Holloway, John H.; Reilley, Charles N.

doi:10.1021/ac60226a025

Cited by 80 publications

(28 citation statements)

References 25 publications

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“…Thus, the reason for the large increase in entropy upon Ca2+ binding did not appear to be structurally based. Since the entropy increase (about 10 kcal/mol) is also observed in organic chelators (16,17), it is reasonable to conclude that the large increase in entropy upon the binding of Ca2+ comes from the release of water molecules bound to Ca2+ in solution.…”

Section: Resultsmentioning

confidence: 83%

Entropic stabilization of a mutant human lysozyme induced by calcium binding.

Kuroki

Kawakita

Nakamura

et al. 1992

Proc. Natl. Acad. Sci. U.S.A.

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The stabilization mechanism of the mutant human lysozyme with a calcium binding site (D86/92) was investigated by using calorimetric approaches. By differential scanning calorimetry, the enthalpy change (Al) in the unfolding of holo-D86/92 was found to be 6.8 kcal/mol smaller than that of the wild-type and apo-D86/92 lysozymes at 85TC.However, the unfolding Gibbs energy change (AG) of the holo mutant was 3.3 kcal/mol greater than the apo type at 85C, indicating a significant decrease of entropy (TAS = 10.1 kcal/mol) in the presence of Ca2 . Subsequently, the Ca2+ binding process in the folded state of the mutant was analyzed by using titration isothermal calorimetry. The binding enthalpy change was estimated to be 4.5 kcal/mol, and AG was -8.1 kcal/mol at 85°C, which indicates that the binding was caused by a large increase in entropy (TAS = 12.6 kcal/mol). From these analyses, the unfolded holo mutant was determined to bind Ca2+ with a binding AG of -4.8 kcal/mol (Al = -2.6 kcal/mol, TAS = 2.2 kcal/mol) at 85°C. Therefore, the major cause of stabilization of holo-D86/92 is the decrease in entropy of the peptide chain due to Ca2+ binding to the unfolded protein.It is known that ligand binding stabilizes a protein (1-3). This kind of stabilization is considered to be very important in biological systems because the stabilization of a protein can be easily regulated by the concentration of ligand in the system (2, 4). The mechanism of the stabilization is stoichiometrically explained by the shift of the folding-unfolding equilibrium to the folded state caused by the higher affinity of ligand to the folded state (5, 6). However, the stabilization mechanism of a protein induced by ligand binding is not so clear from the thermodynamic point of view. The reactions involve not only the change of protein conformation but also the interaction of ligand with water molecules, which makes it complicated to understand the thermodynamic mechanism of the stabilization induced by ligand binding alone. Therefore, the most effective way to clarify the mechanism is the direct analysis ofboth the denaturation and the ligand binding by using calorimetric approaches in conjunction with information of the tertiary structure of a protein. Two kinds of calorimeters are available for this purpose. One is a differential scanning calorimeter used to obtain thermodynamic parameters of protein unfolding (7,8), and the other is a titration calorimeter used to obtain the thermodynamic parameters of binding of a ligand by a protein (9).A mutant human lysozyme (D86/92) that has an engineered Ca2+ binding site (Ka = 5.0 x 106 M-1) was created by replacing both Gln-86 and Ala-92 with aspartic acid (10). This mutant is a suitable model for the investigation of the stabilization mechanism induced by ligand binding because the x-ray structures of the wild-type (11) and the mutant (12) lysozymes have been already solved at 1.8 A. By using both differential scanning calorimetry (DSC) and isothermal differential titration calorimetry (DTC) it wa...

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Section: Resultsmentioning

confidence: 83%

Entropic stabilization of a mutant human lysozyme induced by calcium binding.

Kuroki

Kawakita

Nakamura

et al. 1992

Proc. Natl. Acad. Sci. U.S.A.

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“…For instance, the full straight line representing -A C , shows that for Hg(I1) this quantity decreases on going from n = 2 to n = 3: this is due to the decrease in -A H , (pointed straight line) being larger than the increase in TdS, (dotted straight line). The AH,=-9.2; AS=19atI=O.l [24]. (-dC,)-plots show that for the 3d-cations and Zn2+, 2,3,2-tet forms the most stable complexes.…”

Section: N-methylethylenediamine (= Nmen)mentioning

confidence: 94%

Polyamines XV. Thermodynamics of Metal Complex Formation of Linear Tetraamines Containing Two Ethylenediamine Residues

Anderegg

Bläuenstein

1982

Helvetica Chimica Acta

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SummaryThe complex formation of Co2+, Ni2+, Cu2+, Zn2+, Pb2+ and Hg2+ with three tetraamines of type H2N-(CH2)2-NH-(CH2)n-NH-(CH2)2-NH2 ( = 2, n, 2-tet) for n = 2. 3 and 4, and with N-methylethylenediamine (= nmen) have been investigated at 25" and I=1(KNO3). The stability constants and the heat evolved by formation of the (1 : 1)-complexes ML have been determined. It is shown that the more stable complexes are normally formed by 2,3,2-tet-ligands. These results are discussed relating the thermodynamic data obtained to the stereochemistry of the complexes and using the visible spectra of the complexes in solution. The change in enthalpy is found to be the dominant factor and the measure of the steric strain whereas the entropy of complex formation decreases slowly.

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“…Therefore, the high capacity and low affinity Ca 2ϩ binding by CSQ is likely nonspecific, although the first few ions that bind at low Ca 2ϩ concentrations may have some specificity. Instead of a distinct Ca 2ϩ binding site such as the EF-hand motif (6), pairs of acid residues have been proposed to bind Ca 2ϩ , with Ca 2ϩ binding being driven to a significant degree by the entropy gain from liberation of many water molecules from the hydrated cations (7,8).The crystal structure of rabbit skeletal CSQ (sCSQ) shows that this protein is made up of three domains, each with a thioredoxin fold, which is a five ␤-strand sandwiched by four ␣-helices (9). The individual domains of CSQ show very low sequence similarity with thioredoxins, but the locations of hydrophobic and hydrophilic residues can be overlapped after superimposing the secondary structural components of these two proteins.…”

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confidence: 99%

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confidence: 99%

Comparing Skeletal and Cardiac Calsequestrin Structures and Their Calcium Binding

Park

Kim

et al. 2004

Journal of Biological Chemistry

131

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Calsequestrin, the major calcium storage protein of both cardiac and skeletal muscle, binds and releases large numbers of Ca 2؉ ions for each contraction and relaxation cycle. Here we show that two crystal structures for skeletal and cardiac calsequestrin are nearly superimposable not only for their subunits but also their front-to-front-type dimers. Ca 2؉ binding curves were measured using atomic absorption spectroscopy. This method enables highly accurate measurements even for Ca 2؉ bound to polymerized protein. The binding curves for both skeletal and cardiac calsequestrin were complex, with binding increases that correlated with protein dimerization, tetramerization, and oligomerization. The Ca 2؉ binding capacities of skeletal and cardiac calsequestrin are directly compared for the first time, with ϳ80 Ca 2؉ ions bound per skeletal calsequestrin and ϳ60 Ca 2؉ ions per cardiac calsequestrin, as compared with net charges for these molecules of ؊80 and ؊69, respectively. Deleting the negatively charged and disordered C-terminal 27 amino acids of cardiac calsequestrin results in a 50% reduction of its calcium binding capacity and a loss of Ca 2؉ -dependent tetramer formation. Based on the crystal structures of rabbit skeletal muscle calsequestrin and canine cardiac calsequestrin, Ca 2؉ binding capacity data, and previous lightscattering data, a mechanism of Ca 2؉ binding coupled with polymerization is proposed.Calsequestrin (CSQ) 1 binds and releases large quantities of Ca 2ϩ through its high capacity (40 -50 mol of Ca 2ϩ ion per molecule) and relatively low affinity interactions with Ca 2ϩ (K d ϭ 1 mM) (1). Because of this Ca 2ϩ -buffering capacity of CSQ in the lumenal space, the concentration of free Ca 2ϩ in the sarcoplasmic reticulum (SR) can be maintained below the inhibitory level of the Ca 2ϩ pump (1 mM), and simultaneously, the SR can maintain the ability to rapidly deliver a high capacity Ca 2ϩ signal to the cytoplasm. Even though the lumenal space is minuscule compared with the extracellular space, the high concentrations (ϳ100 mg/ml) of CSQ make the SR an efficient storage compartment for Ca 2ϩ (2).CSQ is associated physically with the RyR protein by a nucleation event that involves CSQ binding to the basic lumenal domains of triadin (3) or junctin (4). These two proteins interact with RyR in the junctional face region of the SR, and this network of interacting proteins assures that high concentrations of Ca 2ϩ are stored very near to the site of Ca 2ϩ release. Ca 2ϩ release from CSQ through the Ca 2ϩ release channel is regulatory but not limiting.The Ca 2ϩ binding and dissociation mechanisms of CSQ are not yet clearly understood. Ca 2ϩ binding sites in CSQ are supposed to be very different from those in the Ca 2ϩ pump (sarco(endo)plasmic reticulum calcium ATPase (SERCA)), calmodulin, and troponin C. CSQ sites need to be made and broken but not over the low cytosolic Ca 2ϩ concentration range or with the same stoichiometry and precision as those formed and subsequently disrupted in the Ca 2ϩ pump or...

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Heat and Entropies of Formation of Metal Chelates of Polyamine and Polyaminocarboxylate Ligands.

Cited by 80 publications

References 25 publications

Entropic stabilization of a mutant human lysozyme induced by calcium binding.

Entropic stabilization of a mutant human lysozyme induced by calcium binding.

Polyamines XV. Thermodynamics of Metal Complex Formation of Linear Tetraamines Containing Two Ethylenediamine Residues

Comparing Skeletal and Cardiac Calsequestrin Structures and Their Calcium Binding

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