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Location of the binding site in subcomponent C1q for plasma fibronectin
Insights
This study clarifies fibronectin binding to C1q, showing both globular and collagen-like regions interact. The specific binding site on C1q for fibronectin is identified within residues 81-97.
Area of Science:
- Immunochemistry
- Molecular Biology
- Protein Interactions
Background:
- Previous research on fibronectin (FN) and C1q interactions presented conflicting findings regarding binding sites.
- Both globular head regions and collagen-like domains of C1q have been implicated in fibronectin binding.
Purpose of the Study:
- To resolve conflicting data on fibronectin binding to C1q.
- To precisely identify the binding domains of C1q responsible for fibronectin interaction.
- To investigate the inhibition of the C1q-fibronectin interaction by C1q digestion products.
Main Methods:
- 125I-labelled fibronectin binding assays were performed using immobilized intact C1q and its collagenase or pepsin digestion products.
- Microtitre plates were used for immobilizing C1q and its fragments.
- Inhibition assays were conducted using C1q digestion products to study the C1q-fibronectin interaction.
Main Results:
- The study confirmed that both globular 'head' region preparations and collagen-like region preparations of C1q can interact with fibronectin.
- Fibronectin binding was observed with both intact C1q and its distinct digestion fragments.
- Inhibition studies provided further evidence for the interaction sites.
Conclusions:
- The binding site for fibronectin on C1q is located within a region encompassing residues 81-97 of each of the three C1q chains.
- This specific region is shared among the fragments studied, explaining the interaction.
- The findings reconcile previous conflicting reports on C1q-fibronectin interactions.
Abstract:
Previous studies on the interaction of fibronectin with C1q have yielded apparently conflicting results since both the globular head regions (produced by collagenase digestion) and the collagen-like domains (produced by limited pepsin digestion) have been reported to bind to fibronectin. In this study, the binding of 125I-labelled fibronectin to either intact C1q, or the collagenase or pepsin digestion products, immobilised on plastic microtitre plates was examined. Inhibition of the C1q-fibronectin interaction by the C1q digestion products was also examined. The results confirmed that both globular 'head' region preparations and collagen-like region preparations, can interact with fibronectin. Since the fragments used in these studies share a section of common amino acid sequence from the C1q molecule it can be concluded that the binding site, on C1q for fibronectin, is located in a region formed from the residues 81-97 of each of the three chains of the C1q molecule.