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Defining the CD59-C9 binding interaction

Yuxiang Huang1, Fei Qiao, Ruben Abagyan

  • 1Department of Microbiology and Immunology, Medical University of South Carolina, South Carolina 29403, USA.

The Journal of Biological Chemistry
|July 18, 2006
PubMed

Insights

Researchers identified a specific 6-residue sequence in complement protein C9 that acts as the primary binding site for CD59. This finding clarifies how CD59 regulates the formation of the membrane attack complex (MAC).

Area of Science:

  • Immunology
  • Complement System Biology

Background:

  • CD59 is a crucial membrane glycoprotein regulating the formation of the cytolytic membrane attack complex (MAC, or C5b-9).
  • CD59 functions by binding to C8 (alpha chain) and C9 during MAC assembly, inhibiting its completion on host cell membranes.

Purpose of the Study:

  • To pinpoint the precise region of human C9 responsible for CD59 recognition.
  • To elucidate the interaction site of CD59 on C8alpha and C9.

Main Methods:

  • Peptide screens and binding assays were employed to identify CD59 interaction domains.
  • Functional assays and computer modeling, including docking studies, were utilized to analyze CD59-protein interactions.

Main Results:

  • A 6-residue sequence (residues 365-371) in human C9 was identified as the primary CD59 recognition domain.
  • Both C8alpha and C9 appear to bind to a similar or overlapping site on CD59.
  • CD59-peptide docking models suggest C9 binds to a hydrophobic pocket on CD59.

Conclusions:

  • The study precisely maps the CD59 recognition site on C9, advancing understanding of MAC regulation.
  • The findings provide a molecular basis for CD59's inhibitory function in the complement cascade.
  • This detailed interaction knowledge could inform therapeutic strategies targeting complement-mediated damage.

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