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Biological functions of C1q expressed by conformational changes
1Institute of Medical Microbiology, Johannes Gutenberg-University, Mainz, W.-Germany.
Behring Institute Mitteilungen
|July 1, 1989
Summary
Serum protein C1q, a highly positively charged molecule, interacts with negatively charged mucopolysaccharides (MPS). This interaction induces conformational changes in C1q, potentially explaining autoantibodies in SLE patients.
Area of Science:
- Biochemistry
- Immunology
- Protein Chemistry
Background:
- C1q is a highly positively charged serum protein with a unique isoelectric point of 9.3.
- Its positive charge enables direct ionic interactions with negatively charged molecules like mucopolysaccharides (MPS).
Purpose of the Study:
- To investigate the interaction between C1q and MPS.
- To explore the conformational changes in C1q upon binding to immune complexes.
- To elucidate the role of these changes in the induction of autoantibodies in Systemic Lupus Erythematosus (SLE).
Main Methods:
- Two-dimensional isoelectric focusing to determine the isoelectric point of C1q.
- Electro-immunoassay to demonstrate the ionic nature of C1q-MPS interaction.
- Hemolytic assay to measure the inhibitory effect of MPS on C1q.
- Detection of neoantigens.
Main Results:
- C1q exhibits a high isoelectric point (9.3), indicating significant positive charge.
- C1q directly interacts ionically with negatively charged MPS.
- Binding of C1q to immune complexes induces conformational changes, evidenced by MPS inhibition and neoantigen detection.
- These conformational changes are long-acting in vitro.
Conclusions:
- The unique charge properties of C1q facilitate its interaction with MPS.
- In vitro studies demonstrate that C1q undergoes conformational changes upon binding to immune complexes.
- These induced, sustained conformational changes in C1q may trigger autoantibody formation against its collagenous portion in SLE patients.