title: Calcium binding characteristics and structural changes of phosvitin.
abstract: Phosvitin is a unique highly phosphorylated protein that plays a role in the regulation of calcification. We conducted a comprehensive study of the chemical, thermodynamic and structural aspects of the interaction of phosvitin with calcium ions using a calcium ion selective electrode (ISE), isothermal titration calorimetry (ITC), circular dichroism spectrum (CD) and fluorescence spectroscopy, respectively. The results showed that under neutral and alkaline conditions, distinct high affinity and low affinity binding modes existed in the interaction between phosvitin and calcium. The high affinity association constant was approximately 10(4)mol(-1), while the binding sites contained nearly 30mol of calcium per mole of phosvitin. This reaction was driven by enthalpy. The unordered and β-turn conformations of phosvitin increased, while the β-sheet conformation decreased. The main interaction forces were electrostatic force, hydrogen bonds or van der Waals force. The low affinity association constant and binding sites were not constant, as many calcium ions were sequestered by phosvitin. The binding reaction was driven by entropy, and the β-sheet conformation of phosvitin increased while the unordered conformation decreased. The main interaction force was hydrophobic force. However, under acidic conditions, the interaction between phosvitin and calcium was an entropy-driven endothermic reaction, and the main interaction force was weak hydrophobic force. This calcium-binding characteristic of phosvitin may play a specific role in its biological function.
authors.affiliation: National R&D Center for Egg Processing, College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, PR China.
authors.forename: Xiaowei
authors.initials: X
authors.lastname: Zhang
authors.affiliation: National R&D Center for Egg Processing, College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, PR China.
authors.forename: Fang
authors.initials: F
authors.lastname: Geng
authors.affiliation: National R&D Center for Egg Processing, College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, PR China.
authors.forename: Xi
authors.initials: X
authors.lastname: Huang
authors.affiliation: National R&D Center for Egg Processing, College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, PR China. Electronic address: mameihuhn@163.com.
authors.forename: Meihu
authors.initials: M
authors.lastname: Ma
mesh_terms: D002118:Calcium / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D010774:Phosvitin / Q000737:chemistry*; D017433:Protein Structure, Secondary; D055672:Static Electricity; D013816:Thermodynamics
chemical_list: D010774:Phosvitin; D002118:Calcium
keywords: Binding characteristic; Calcium; Isothermal titration calorimetry; Phosvitin