Binding specificity of mouse serum amyloid P-component for fibronectin

Area of Science:

• Biochemistry
• Molecular Biology
• Immunology

Background:

• Serum amyloid P-component (SAP) is a major soluble component of the amyloid P component family.
• Plasma fibronectin (Fn) is a high molecular weight glycoprotein involved in cell adhesion, migration, and wound healing.

Purpose of the Study:

• To investigate the binding characteristics between purified mouse serum amyloid P-component (SAP) and plasma fibronectin (Fn).
• To identify the specific binding site and conditions required for SAP-Fn interaction.

Main Methods:

• Protein immobilization using specific antibodies.
• Saturation binding assays to determine molar ratios.
• Inhibition assays using monoclonal antibodies, gelatin, and heparin.
• Calcium ion (Ca++) concentration dependency studies.

Main Results:

• SAP and Fn binding was confirmed when either protein was immobilized.
• Binding was cooperative and saturable, with distinct molar ratios at saturation (SAP/Fn = 7.1 and 3.7).
• The interaction required 2-3mM Ca++.
• Binding was inhibited by anti-Fn antibody, soluble gelatin, and heparin in the presence of Ca++.

Conclusions:

• The SAP binding site on Fn is localized to the mid-molecule region.
• This region encompasses adjacent gelatin-binding and heparin-I binding domains.
• Calcium ions are crucial for mediating the SAP-Fn interaction.