Neisseria meningitidis RTX Protein FrpC Induces High Levels of Serum Antibodies during Invasive Disease: Polymorphism of frpC Alleles and Purification of Recombinant FrpC

Abstract

The Neisseria meningitidis FAM20 strain secretes two proteins of unknown function, FrpA and FrpC, which contain typical RTX domains found in cytotoxins from other gram-negative pathogens. To evaluate whether the Frp proteins could be involved in meningococcal virulence, 65 isolates of all serogroups were screened by PCR for the presence of both frp genes. The frpA allele was, however, poorly conserved. A single strain harbored an frpA allele of the previously described size, while large insertions were detected in the frpA loci of 22 isolates (34%), and the 42 remaining isolates (65%) did not contain frpA at all. In contrast, frpC alleles, albeit of variable length, were detected in all invasive and most carrier strains. This suggests that meningococci may produce a family of FrpC proteins of various molecular masses. High levels of both immunoglobulin G (IgG) and IgA class antibodies recognizing recombinant FrpC were indeed detected in convalescent-phase sera of most patients at 2 and 4 to 5 weeks after the first symptoms of meningococcal disease. These results show that FrpC-like proteins are produced and may play a role in invasive meningococcal infections.

Transcriptomic buffering of cryptic genetic variation contributes to meningococcal virulence

“…[21, 38–40], see Additional file 2: S1) only 8 are missing in strain α522, and strain α522 lacks in particular large parts of the islands of horizontal transfer B and C that code for a two-partner secretion system involved in host cell adhesion [41] (Additional file 1: Figure S2A). It further lacks almost the entire repeat-in-toxin island 1 encoding FrpA/C-like proteins which induce high levels of serum antibodies during invasive disease in humans [42]. In addition, downstream of glnB encoding the signal-transducing nitrogen regulatory protein PII strain α522 also lacks nadA which codes for a minor adhesin that was found to promote bacterial adhesion to and penetration into human epithelial cells in vitro [43].…”

Genomic Investigation into Strain Heterogeneity and Pathogenic Potential of the Emerging Gastrointestinal Pathogen Campylobacter ureolyticus

“…Various numbers of such repeats are found in the RTX domains of several cytotoxins/leukotoxins involved in the virulence of a number of different Gram-negative genera [64]. A characteristic feature of these exoproteins is the use of type I secretion systems to facilitate protein export across the bacterial envelope into the extracellular space [65]; their functionality being limited by Ca 2+ ion availability, which serves to sequester activity until outside of the bacterial cell [65].…”

Campylobacter ureolyticus

“…Further to this, 3 of the secreted RTX hemolysins show evidence of iron regulation with homology to the FrpC RTX protein of Neisseria meningitidis. The detection of antibodies directed against the FrpC protein in the serum of patients infected with the pathogen demonstrates that this protein is produced in vivo during the infection cycle; however its exact role remains unclear 68 - 70 . The release of high levels of toxins causes cells to lyse as pores formed by the toxin allow cytoplasmic contents to leak out of the cell 71 .…”