The first EGF-like domain from human factor IX contains a high-affinity calcium binding site

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Chemistry

Background:

• Vitamin K-dependent plasma proteins, including coagulation factors IX, X, protein C, and protein S, are crucial for hemostasis.
• Epidermal growth factor-like (EGF-like) domains with conserved carboxylate residues are hypothesized to mediate high-affinity calcium binding in these proteins.

Purpose of the Study:

• To investigate the calcium-binding properties of the first epidermal growth factor-like domain of human factor IX.
• To test the hypothesis that EGF-like domains are responsible for high-affinity calcium binding in vitamin K-dependent proteins.

Main Methods:

• Expression of the first EGF-like domain (residues 46-84) from human factor IX using a yeast secretion system.
• 1H-NMR spectroscopy was employed to detect calcium-dependent shifts and analyze the aromatic region of the NMR spectrum.
• NOESY and COSY experiments were utilized for spectral assignment and conformational analysis.

Main Results:

• A high-affinity calcium binding site (Kd = 200-300 microM) was detected in the human factor IX EGF-like domain, evidenced by a calcium-dependent shift of Tyr69.
• The aromatic region of the NMR spectrum was fully assigned, providing insights into the domain's structure.
• The study discussed the influence of calcium and pH on the domain's conformation, referencing the structure of human EGF.

Conclusions:

• The findings support the hypothesis that EGF-like domains possess high-affinity calcium-binding capabilities.
• It is suggested that other similar EGF-like domains may exhibit comparable calcium-binding properties.
• The study provides structural insights into the conformational effects of calcium and pH on EGF-like domains.