Sialylation of lipopolysaccharide by CMP-NANA in viable gonococci is enhanced by low M r material released from blood cell extracts but not by some UDP sugars

Abstract

Serum resistance of gonococci in most patients is due to sialylation of a Galβ1-4GlcNAc group on a conserved 4.5 kDa lipopolysaccharide (LPS) component by host cytidine 5′-monophospho-N-acetyl neuraminic acid (CMP-NANA) catalysed by a gonococcal sialyl transferase. This sialylation is enhanced by a low M r factor(s) which, like CMP-NANA, is released in diffusates from high M r fractions obtained from sonicates dialysed at 4°C. Also, as shown here, this factor(s) is released when the sonicates are dialysed at 18-20°C. The enhancement of sialylation, first demonstrated using enzymes in gonococcal extracts, has been shown to occur in live gonococci and hence probably to have a role in pathogenicity. Gonococci, emerging from lag phase and incubated for 2 h with CMP- 14CNANA fixed up to 90% more radiolabel than controls when the second factor(s) was present; their LPS separated by SDS-PAGE contained more radiolabel than control samples and label was not detected in any other component. Fractions with enhancing activity absorbed maximally at about 260 nm but a mixture of UDP-galactose (UDP-Gal), UDP-N-Acetyl galactosamine (UDP-GalNAc), UDP-glucose (UDP-Glc) and UDP-N-Acetyl glucosamine (UDP-GlcNAc) showed no significant enhancing activity. The enhancing action of the low M r fractions was unaffected by incubation with β-galactosidase.