A Novel Sialic Acid Binding Site on Factor H Mediates Serum Resistance of Sialylated Neisseria gonorrhoeae

Abstract

SummaryFactor H (fH), a key alternative complement pathway regulator, is a cofactor for factor I-mediated cleavage of C3b. fH consists of 20 short consensus repeat (SCR) domains. Sialic acid binding domains have previously been localized to fH SCRs 6-10 and 13. To examine fH binding on a sialylated microbial surface, we grew Neisseria gonorrhoeae in the presence of 5 Ј -cytidinemonophospho-N -acetylneuraminic acid, which sialylates lipooligosaccharide and converts to serum resistance gonococci previously sensitive to nonimmune serum killing. fH domains necessary for binding sialylated gonococci were determined by incubating organisms with recombinant human fH (rH) and nine mutant rH molecules (deletions spanning the entire fH molecule). rH and all mutant rH molecules that contained SCRs 16-20 bound to the sialylated strain; no mutant molecule bound to serum-sensitive nonsialylated organisms. Sialic acid was demonstrated to be the fH target by flow cytometry that showed a fourfold increase in fH binding that was reversed by neuraminidase-mediated cleavage of sialic acid off gonococci. Functional specificity of fH was confirmed by decreased total C3 binding and almost complete conversion to iC3b on sialylated gonococci. Sialic acid can therefore bind fH uniquely through SCRs 16-20. This blocks complement pathway activation for N. gonorrhoeae at the level of C3.

Human complement activation by smooth and rough Proteus mirabilis lipopolysaccharides

“…The differences between variations (compared with S1959) were analyzed by ANOVA. LPS protecting bacteria from human serum has also been observed by others (Joiner et al 1986;Nawrot et al 1995;Ram et al 1998). One can postulate that the smooth LPS forms activate complement and deposit C3 on the long polysaccharide chains and in this way keep MAC formation at a distance from the bacterial cell membrane.…”

“…Complement system activation is an important factor in the human defense system against bacterial pathogens (Burns and Hull 1998;Fischer et al 1997;Joiner et al 1986;Nawrot et al 1995;Ram et al 1998). The presence of O-polysaccharide on the surface of the P. mirabilis S1959 strain protected that strain from complementmediated lysis.…”

The role of complement receptor 3 (CR3) inNeisseria gonorrhoeaeinfection of human cervical epithelia

“…Although strain-specific properties have been associated with resistance to complement-mediated killing (i.e. serum resistance) in vitro, most clinically isolated gonococci initially exhibit serum resistance (Densen, 1989;de la Paz et al, 1995;Ram et al, 1998;Vogel and Frosch, 1999). Ram et al (1998) suggested that an increased conversion of C3b to iC3b on the gonococcal surface might contribute to serum resistance in vivo.…”

“…Several lines of evidence suggest that C H alternative pathway inactivation occurs with N. gonorrhoeae infection (Densen et al, 1982;Densen, 1989;Wetzler et al, 1992;de la Paz et al, 1995;Ram et al, 1998;Jarvis et al, 1999;McQuillen et al, 1999;Vogel and Frosch, 1999). This prompted us to examine the role of CR3 in N. gonorrhoeae infection of the cervical epithelium.…”

Haemophilus parasuis α-2,3-sialyltransferase-mediated lipooligosaccharide sialylation contributes to bacterial pathogenicity

“…For whole cell ELISA, the assay was performed as previously described with slight modifications [55]. Briefly, 10 8 CFU of bacteria were incubated with 20 μL of normal porcine serum (60 min at 37°C) as described above for western blotting.…”