Competitive calcium ion binding to end-tethered weak polyelectrolytes

Soft Matter ◽  
2018 ◽  
Vol 14 (12) ◽  
pp. 2365-2378 ◽  
Author(s):  
Rikkert J. Nap ◽  
Sung Hyun Park ◽  
Igal Szleifer
Keyword(s):  
Calcium Ion ◽  
Structural Changes ◽  
Molecular Model ◽  
Ion Concentration ◽  
Ion Binding ◽  
Spherical Nanoparticles ◽  
Planar Surfaces ◽  
Calcium Ion Binding ◽  
Weak Polyelectrolytes

We have developed a molecular model to describe the structural changes and potential collapse of weak polyelectrolyte layers end-tethered to planar surfaces and spherical nanoparticles as a function of pH and divalent ion concentration.

scholarly journals Calcium-binding parameter of Bacillus amyloliquefaciens α-amylase determined by inactivation kinetics

2002 ◽  
Vol 364 (3) ◽  
pp. 635-639 ◽  
Author(s):  
Atsushi TANAKA ◽  
Eiichi HOSHINO
Keyword(s):  
Kinetic Model ◽  
Calcium Ion ◽  
Calcium Binding ◽  
Bacillus Amyloliquefaciens ◽  
Ion Concentration ◽  
Ion Binding ◽  
Enzyme Protein ◽  
Enthalpy And Entropy ◽  
Calcium Ion Binding ◽  
Calcium Ion Concentration

The irreversible thermal inactivation and the thermodynamics of calcium ion binding of Bacillus amyloliquefaciens α-amylase in the absence of substrates were studied. The enzyme inactivation on heating was apparently followed by first-order kinetics. The enzyme was stabilized with an increased concentration of calcium ion and thus the inactivation was highly dependent on the state of calcium binding. The activation parameter for the inactivation suggests an unfolding of the enzyme protein upon heating. Values of both the activation enthalpy and entropy were increased with a higher calcium ion concentration. An inactivation kinetic model is based on the assumption of a two-stage unfolding transition in which the bivalent ion dissociation occurs in the first step followed by the secondary structural unfolding. This simple kinetic model provides both a qualitative and quantitative interpretation of calcium ion binding to the enzyme and its effect on the inactivation properties. The specific approximations of the kinetic model were strictly followed in the analysis to calculate the apparent inactivation rate at each calcium ion concentration in terms of the calcium-binding parameters. The enthalpy and entropy changes for the calcium ion binding were calculated to be −149kJ/mol and −360J·mol−1·K−1 respectively and these values suggest a strong enthalpic affinity for the bivalent ion binding to the enzyme protein. The thermodynamical interpretation attempts to provide clear relations between the terms of an apparent inactivation rate and the calcium binding.

scholarly journals Roles of Disulfide Linkage and Calcium Ion-Mediated Interactions in Assembly and Disassembly of Virus-Like Particles Composed of Simian Virus 40 VP1 Capsid Protein

2001 ◽  
Vol 75 (1) ◽  
pp. 61-72 ◽  
Author(s):  
Ken-Ichiro Ishizu ◽  
Hajime Watanabe ◽  
Song-Iee Han ◽  
Shin-Nosuke Kanesashi ◽  
Mainul Hoque ◽  
...  
Keyword(s):  
Amino Acid ◽  
Calcium Ion ◽  
Insect Cells ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
Ion Binding ◽  
Amino Acid Substitutions ◽  
Disulfide Linkage ◽  
Calcium Ion Binding

ABSTRACT The simian virus 40 capsid is composed of 72 pentamers of VP1 protein. Although the capsid is known to dissociate to pentamers in vitro following simultaneous treatment with reducing and chelating agents, the functional roles of disulfide linkage and calcium ion-mediated interactions are not clear. To elucidate the roles of these interactions, we introduced amino acid substitutions in VP1 at cysteine residues and at residues involved in calcium binding. We expressed the mutant proteins in a baculovirus system and analyzed both their assembly into virus-like particles (VLPs) in insect cells and the disassembly of those VLPs in vitro. We found that disulfide linkages at both Cys-9 and Cys-104 conferred resistance to proteinase K digestion on VLPs, although neither linkage was essential for the formation of VLPs in insect cells. In particular, reduction of the disulfide linkage at Cys-9 was found to be critical for VLP dissociation to VP1 pentamers in the absence of calcium ions, indicating that disulfide linkage at Cys-9 prevents VLP dissociation, probably by increasing the stability of calcium ion binding. We found that amino acid substitutions at carboxy-terminal calcium ion binding sites (Glu-329, Glu-330, and Asp-345) resulted in the frequent formation of unusual tubular particles as well as VLPs in insect cells, indicating that these residues affect the accuracy of capsid assembly. In addition, unexpectedly, amino acid substitutions at any of the calcium ion binding sites tested, especially at Glu-157, resulted in increased stability of VLPs in the absence of calcium ions in vitro. These results suggest that appropriate affinities of calcium ion binding are responsible for both assembly and disassembly of the capsid.

Calcium ion-binding study on α-elastin

1974 ◽  
Vol 371 (2) ◽  
pp. 526-533 ◽  
Author(s):  
G. Abatangelo ◽  
D. Daga-Gordini ◽  
G. Garbin ◽  
R. Cortivo
Keyword(s):  
Calcium Ion ◽  
Binding Study ◽  
Ion Binding ◽  
Calcium Ion Binding

Some observations on the calcium ion binding to the eggshell matrix

1978 ◽  
Vol 26 (1) ◽  
pp. 247-252 ◽  
Author(s):  
G. Abatangelo ◽  
D. Daga-Gordini ◽  
I. Castellani ◽  
R. Cortivo
Keyword(s):  
Calcium Ion ◽  
Ion Binding ◽  
Calcium Ion Binding ◽  
Eggshell Matrix
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