Single-molecule kinetics of pore assembly by the membrane attack complex

Nat Commun. 2019 May 6;10(1):2066. doi: 10.1038/s41467-019-10058-7.


The membrane attack complex (MAC) is a hetero-oligomeric protein assembly that kills pathogens by perforating their cell envelopes. The MAC is formed by sequential assembly of soluble complement proteins C5b, C6, C7, C8 and C9, but little is known about the rate-limiting steps in this process. Here, we use rapid atomic force microscopy (AFM) imaging to show that MAC proteins oligomerize within the membrane, unlike structurally homologous bacterial pore-forming toxins. C5b-7 interacts with the lipid bilayer prior to recruiting C8. We discover that incorporation of the first C9 is the kinetic bottleneck of MAC formation, after which rapid C9 oligomerization completes the pore. This defines the kinetic basis for MAC assembly and provides insight into how human cells are protected from bystander damage by the cell surface receptor CD59, which is offered a maximum temporal window to halt the assembly at the point of C9 insertion.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • CD59 Antigens / metabolism*
  • Cell Membrane / metabolism
  • Cell Membrane / ultrastructure*
  • Complement C5 / metabolism
  • Complement C8 / metabolism
  • Complement C9 / metabolism*
  • Complement Membrane Attack Complex / metabolism*
  • Humans
  • Kinetics
  • Microscopy, Atomic Force / methods
  • Protein Multimerization*
  • Single Molecule Imaging / methods


  • CD59 Antigens
  • Complement C5
  • Complement C8
  • Complement C9
  • Complement Membrane Attack Complex
  • CD59 protein, human
  • complement C5b-7 complex