title: Distinct localization of the complement C5b-9 complex on Gram-positive bacteria.
abstract: The plasma proteins of the complement system fulfil important immune defence functions, including opsonization of bacteria for phagocytosis, generation of chemo-attractants and direct bacterial killing via the Membrane Attack Complex (MAC or C5b-9). The MAC is comprised of C5b, C6, C7, C8, and multiple copies of C9 that generate lytic pores in cellular membranes. Gram-positive bacteria are protected from MAC-dependent lysis by their thick peptidoglycan layer. Paradoxically, several Gram-positive pathogens secrete small proteins that inhibit C5b-9 formation. In this study, we found that complement activation on Gram-positive bacteria in serum results in specific surface deposition of C5b-9 complexes. Immunoblotting revealed that C9 occurs in both monomeric and polymeric (SDS-stable) forms, indicating the presence of ring-structured C5b-9. Surprisingly, confocal microscopy demonstrated that C5b-9 deposition occurs at specialized regions on the bacterial cell. On Streptococcus pyogenes, C5b-9 deposits near the division septum whereas on Bacillus subtilis the complex is located at the poles. This is in contrast to C3b deposition, which occurs randomly on the bacterial surface. Altogether, these results show a previously unrecognized interaction between the C5b-9 complex and Gram-positive bacteria, which might ultimately lead to a new model of MAC assembly and functioning.
authors.affiliation: Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, the Netherlands.
authors.forename: Evelien T M
authors.initials: ET
authors.lastname: Berends
authors.forename: Johanna F
authors.initials: JF
authors.lastname: Dekkers
authors.forename: Reindert
authors.initials: R
authors.lastname: Nijland
authors.forename: Annemarie
authors.initials: A
authors.lastname: Kuipers
authors.forename: Jasper A
authors.initials: JA
authors.lastname: Soppe
authors.forename: Jos A G
authors.initials: JA
authors.lastname: van Strijp
authors.forename: Suzan H M
authors.initials: SH
authors.lastname: Rooijakkers
mesh_terms: D001665:Binding Sites; D002473:Cell Wall / Q000276:immunology*; D003179:Complement C3b / Q000276:immunology; D015938:Complement Membrane Attack Complex / Q000276:immunology*; D006094:Gram-Positive Bacteria / Q000276:immunology*; D006801:Humans; D010457:Peptidoglycan / Q000276:immunology; D011485:Protein Binding / Q000276:immunology
chemical_list: D015938:Complement Membrane Attack Complex; D010457:Peptidoglycan; D003179:Complement C3b