Defining targets for complement components C4b and C3b on the pathogenic neisseriae.
Complement is a key arm of the innate immune defenses against the pathogenic neisseriae. We previously identified lipooligosaccharide on Neisseria meningitidis as an acceptor for complement C4b. Little is known about other neisserial targets for complement proteins C3 and C4, which covalently attach to bacterial surfaces and initiate opsonization and killing. In this study we demonstrate that Neisseria gonorrhoeae porin (Por) 1B selectively binds C4b via amide linkages and C3b via ester linkages. Using strains expressing hybrid Por1A/1B molecules, a region spanned by loops 4 and 5 of Por1B was identified as the preferred binding site for C4b. We also identified the opacity protein (Opa), a major adhesin of pathogenic neisseriae, as a target for C4b and C3b on both N. meningitidis and N. gonorrhoeae. Using N. gonorrhoeae variants that predominantly expressed individual Opa proteins, we found that all Opa proteins tested (A, B, C, D, E, F, and I) bound C4b and C3b via amide and ester linkages, respectively. Amide linkages with Por1B and Opa were confirmed using serum containing only the C4A isoform, which exclusively forms amide linkages with targets. While monomers and heterodimers of C4Ab were detected on bacterial targets, C4Bb appeared to preferentially participate in heterodimer (C5 convertase) formation. Our data provide another explanation for the enhanced serum sensitivity of Por1B-bearing gonococci. The binding of C3b and C4b to Opa provides a rationale for the recovery of predominantly "transparent" (Opa-negative) neisserial isolates from persons with invasive disease, where the bacteria encounter high levels of complement.
Lewis
Lisa A
LA
Division of Infectious Diseases and Immunology, University of Massachusetts Medical School, Lazare Research Building, Room 370I, 364 Plantation Street, Worcester, MA 01605, USA. lisa.lewis@umassmed.edu
Ram
Sanjay
S
Prasad
Alpana
A
Gulati
Sunita
S
Getzlaff
Silke
S
Blom
Anna M
AM
Vogel
Ulrich
U
Rice
Peter A
PA
D001425:Bacterial Outer Membrane Proteins; D003179:Complement C3b / Q000276:immunology*; D015935:Complement C4b / Q000276:immunology*; D006801:Humans; D009344:Neisseria gonorrhoeae / Q000276:immunology*; D009345:Neisseria meningitidis / Q000276:immunology*; D018272:Porins; D011485:Protein Binding; D020033:Protein Isoforms
D001425:Bacterial Outer Membrane Proteins; D018272:Porins; D020033:Protein Isoforms; C057699:porin protein, Neisseria; C090348:Opa protein, Neisseria; D003179:Complement C3b; D015935:Complement C4b