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Chimeras of human complement C9 reveal the site recognized by complement regulatory protein CD59
T Hüsler1, D H Lockert, K M Kaufman
1Blood Research Institute, Southeastern Wisconsin, Milwaukee, 53201-2178.
The Journal of Biological Chemistry
|February 24, 1995
Summary
CD59 antigen protects human cells from complement-mediated lysis. Researchers identified residues 334-415 in human complement C9 as the specific binding site for CD59, explaining its species-selective inhibition.
Area of Science:
- Immunology
- Molecular Biology
- Complement System
Background:
- CD59 antigen is a crucial complement regulatory protein.
- It prevents cell lysis by inhibiting the C5b-9 membrane attack complex.
- CD59's inhibitory function is known to be species-selective.
Purpose of the Study:
- To pinpoint the exact peptide segment of human complement C9 recognized by CD59.
- To elucidate the molecular basis for CD59's species-selective activity.
Main Methods:
- Isolation and characterization of rabbit C9 cDNA clones.
- Construction of human/rabbit C9 chimeric cDNAs for expression in COS-7 cells.
- Hemolytic assays using chicken erythrocytes and CD59 to test chimera activity.
Main Results:
- Human/rabbit C9 chimeras were hemolytically active.
- CD59 inhibited chimeras containing human C9 sequence from residues 334-415.
- Chimeras with rabbit C9 sequence in this region were not inhibited by CD59.
Conclusions:
- Human C9 residues 334-415 constitute the binding site for CD59.
- Sequence variations within this C9 segment explain CD59's species-selective inhibition.
- This finding advances understanding of complement regulation and immune evasion.