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Divalent cation modulation of fibronectin binding to heparin and to DNA
Insights
Fibronectin fragment binding to heparin and DNA is modulated by divalent cations. Calcium ions specifically affect certain fibronectin fragments, while others are sensitive to various cations.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Adhesion
Background:
- Fibronectin is a crucial adhesive glycoprotein involved in cell adhesion and extracellular matrix assembly.
- Its interactions with heparin and DNA are vital for various biological processes.
- Understanding these interactions is key to deciphering fibronectin's role in health and disease.
Purpose of the Study:
- To investigate the influence of divalent cations on the binding of human plasma fibronectin tryptic fragments to heparin and DNA.
- To characterize the different binding affinities and cation sensitivities of specific fibronectin fragments.
Main Methods:
- Tryptic digestion of human plasma fibronectin to generate distinct fragments.
- Analysis of fragment binding to heparin and DNA under varying divalent cation concentrations (CaCl2, MgCl2, MnCl2).
- Identification and characterization of specific fibronectin fragments (e.g., 31,000-dalton, 75,000-dalton, 95,000-dalton) and their binding properties.
Main Results:
- Identified three distinct binding patterns of fibronectin fragments to heparin based on cation sensitivity.
- Calcium-sensitive binding was observed for the NH2-terminal 31,000-dalton fragment (fragment 23).
- Divalent cation-sensitive and insensitive binding were characterized for 75,000-dalton (fragment 13) and 95,000-dalton (fragment 10) fragments, respectively.
- Fibronectin fragments bind DNA in the presence of EDTA, but this binding is abolished by CaCl2 or MgCl2.
Conclusions:
- Divalent cations play a significant role in modulating the binding of specific fibronectin domains to heparin and DNA.
- Different fibronectin fragments exhibit unique cation-dependent binding characteristics.
- These findings provide insights into the regulatory mechanisms of fibronectin-ligand interactions.
Abstract:
Fibronectin is an adhesive glycoprotein that binds to heparin and to DNA. The binding of tryptic fragments of human plasma fibronectin to these ligands is found to be highly dependent on the concentration of divalent cations. We have identified 3 types of binding to heparin. 1) Calcium-sensitive binding is inhibited by CaCl2, but not by MgCl2 or by MnCl2. The NH2-terminal 31,000-dalton fragment (fragment 23) has this type of binding, which is half-maximally inhibited by 3 to 4 mM CaCl2. 2) Divalent cation-sensitive binding is exhibited by a 75,000-dalton fragment (fragment 13); its binding is inhibited by all 3 divalent cations. 3) Divalent cation-insensitive binding is characteristic of a 95,000-dalton fragment (fragment 10) and larger fragments. These 3 fragments (fragments 10, 13, and 23) are not disulfide-bonded to other fragments. Specific tryptic fragments of fibronectin also bind readily to native DNA in the presence of EDTA, but the binding of all fragments is abolished by the presence of 10 mM CaCl2 or MgCl2. Our results indicate that the binding of specific domains of fibronectin to heparin or to DNA can be modulated by divalent cations.