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The membrane attack mechanism of complement. Reversible interactions among the five native components in free
The Journal of Experimental Medicine
|August 1, 1973
Summary
Complement proteins C5-9 interact in solution, forming a stable membrane attack complex. This study details specific reversible interactions between complement components, crucial for understanding immune response.
Area of Science:
- Immunology
- Molecular Biology
- Biochemistry
Background:
- The membrane attack complex (MAC) is essential for the complement system's cytolytic function.
- Understanding the assembly and interactions of MAC proteins (C5-9) is key to deciphering complement-mediated cell lysis.
Purpose of the Study:
- To investigate the reversible interactions between individual complement proteins (C5, C6, C7, C8, C9) in free solution.
- To characterize the formation and properties of the C5-9 complex.
Main Methods:
- Sedimentation analysis was used to detect and characterize protein-protein interactions.
- Experiments were conducted under varying ionic strengths and pH to determine optimal conditions for complex formation.
Main Results:
- Specific reversible interactions were observed between C5 and C8, C5-7 and C8, and C8 and C9.
- Complex formation was pH-independent (6.5-8.5) and enhanced by low ionic strength and excess C8.
- All five native proteins (C5-9) formed an association product sedimenting at 10.8-11.2S, supporting a stable multimolecular complex.
Conclusions:
- Complement proteins C5-9 reversibly interact in free solution to form a stable, functional MAC.
- These findings support the model of C5-9 assembly into a multimolecular complex prior to or upon target membrane binding.