Comparison between complement and melittin hemolysis: anti-melittin antibodies inhibit complement lysis

Area of Science:

• Immunology
• Biochemistry
• Cell Biology

Background:

• Melittin and complement component 9 (C9) exhibit similar hemolytic activity and pore formation in erythrocytes.
• Metal ions suppress the hemolytic action of both melittin and C9 at comparable concentrations, hinting at a shared mechanism.

Purpose of the Study:

• To investigate the mechanism of hemolysis mediated by melittin and C9.
• To determine if antibodies against melittin can inhibit C9-mediated hemolysis and elucidate the underlying interactions.

Main Methods:

• Hemolysis assays using erythrocytes treated with melittin and C9.
• Immunoassays (e.g., Western blots) to detect antibody-antigen interactions.
• Analysis of sequence homology between melittin and C9.
• Inhibition assays to assess the effect of anti-melittin antibodies on C9 binding and lysis.

Main Results:

• Polyclonal anti-melittin immunoglobulin G (IgG) specifically inhibited human C9-mediated hemolysis.
• Antibodies reacted with human and monkey C9 but not C9 from lower animals, ruling out reaction with conserved structures like amphipathic helices.
• Anti-melittin IgG recognized an epitope between residues 245-390 of human C9 and did not block C9 binding to the C5b-8 complex.
• Homology was found between melittin residues 8-16 and human C9 residues 292-295 and 527-531.

Conclusions:

• Anti-melittin antibodies inhibit C9 hemolysis by interfering with a post-binding event, likely by binding to a conformational epitope on native C9.
• This binding retards the unfolding of C9, a process necessary for membrane insertion and subsequent hemolysis.
• The findings suggest a potential shared structural or mechanistic basis for the hemolytic actions of melittin and C9.