Bacterial killing by complement requires direct anchoring of membrane attack complex precursor C5b-7

An important effector function of the human complement system is to directly kill Gram-negative bacteria via Membrane Attack Complex (MAC) pores. MAC pores are assembled when surface-bound convertase enzymes convert C5 into C5b, which together with C6, C7, C8 and multiple copies of C9 forms a transm...

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Bibliographic Details
Published in:PLoS pathogens 2020-06, Vol.16 (6), p.e1008606-e1008606
Main Authors: Doorduijn, Dennis J., Bardoel, Bart W., Heesterbeek, Dani A. C., Ruyken, Maartje, Benn, Georgina, Parsons, Edward S., Hoogenboom, Bart W., Rooijakkers, Suzan H. M.
Format: Article
Language:English
Subjects:
Anchoring
Assembly
Atomic force microscopy
Bacteria
Biology and Life Sciences
Complement
Complement system
E coli
Flow cytometry
Gram-negative bacteria
Medicine and Health Sciences
Membrane attack complex
Membranes
Molecular biology
Nanotechnology
Pores
Porosity
Research and Analysis Methods
Strains (organisms)
Supervision
Trypsin
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Summary:An important effector function of the human complement system is to directly kill Gram-negative bacteria via Membrane Attack Complex (MAC) pores. MAC pores are assembled when surface-bound convertase enzymes convert C5 into C5b, which together with C6, C7, C8 and multiple copies of C9 forms a transmembrane pore that damages the bacterial cell envelope. Recently, we found that bacterial killing by MAC pores requires local conversion of C5 by surface-bound convertases. In this study we aimed to understand why local assembly of MAC pores is essential for bacterial killing. Here, we show that rapid interaction of C7 with C5b6 is required to form bactericidal MAC pores on Escherichia coli. Binding experiments with fluorescently labelled C6 show that C7 prevents release of C5b6 from the bacterial surface. Moreover, trypsin shaving experiments and atomic force microscopy revealed that this rapid interaction between C7 and C5b6 is crucial to efficiently anchor C5b-7 to the bacterial cell envelope and form complete MAC pores. Using complement-resistant clinical E. coli strains, we show that bacterial pathogens can prevent complement-dependent killing by interfering with the anchoring of C5b-7. While C5 convertase assembly was unaffected, these resistant strains blocked efficient anchoring of C5b-7 and thus prevented stable insertion of MAC pores into the bacterial cell envelope. Altogether, these findings provide basic molecular insights into how bactericidal MAC pores are assembled and how bacteria evade MAC-dependent killing.
ISSN:1553-7374
1553-7366
1553-7374
DOI:10.1371/journal.ppat.1008606