Sialyltransferase (Stase) in Neisseria gonorrhoeae organisms (gonococci [GC]) transfers sialic acid (Nacetylneuraminic acid [NANA]) from cytidine 5-monophospho-N-acetylneuraminic acid (CMP-NANA) mainly to the terminal galactose (Gal) residue in the Gal -1,4 N-acetylglucosamine (Gal-GlcNAc)-R lipooligosaccharide (LOS) structure. Sialylated GC resist killing by normal human serum, sometimes show reduced invasion of epithelial cells, and have reduced adhesion to and stimulation of human neutrophils. We questioned whether Stase itself modulates the interactions of GC with human epithelial cells and neutrophils in the absence of exogenous CMP-NANA. To that end, we treated strain F62 with ethyl methanesulfonate and grew ϳ175,000 colonies on CMP-NANA plates, and screened them with monoclonal antibody 1B2-1B7 (MAb 1B2). MAb 1B2 is specific for Gal-GlcNAc and reacts only with asialylated GC. We isolated 13 MAb 1B2-reactive mutants, including five null mutants, that had Stase activities ranging from barely detectable to fivefold less than that of wild-type (WT) F62. The LOS phenotype of Stase null mutants was identical to that of WT F62, yet the mutants could not sialylate their LOS when grown with CMP-NANA. The Stase null phenotype was rescuable to Stase ؉ by transformation with chromosomal DNA from WT F62. Stase null mutants remained serum sensitive even when grown with CMP-NANA. One Stase null mutant, ST94A, adhered to and invaded the human cervical epithelial cell line ME-180 at levels indistinguishable from that of WT F62 in the absence of CMP-NANA. In human neutrophil studies, ST94A stimulated the oxidative burst in and adhered to human neutrophils at levels similar to those of WT F62. ST94A and WT F62 were also phagocytically killed by neutrophils at similar levels. These results indicate that expression of Stase activity is not required for interaction of GC with human cells. Neisseria gonorrhoeae organisms (gonococci [GC]) use hostderived cytidine 5Ј-monophospho-N-acetylneuraminic acid (CMP-NANA) and their own sialyltransferase (Stase) to sialylate mainly the galactose (Gal) residue of the 4.5-kDa Gal -1,4 N-acetylglucosamine (Gal-GlcNAc)-R lipooligosaccharide (LOS) structure (25, 28; reviewed in references 19, 33, 38, and 39). Sialylation of LOS results in resistance of GC to killing by normal human serum (NHS) (2, 25, 28; reviewed in references 33, 38, and 39) and by some (8, 47) but not other (6) anti-porin protein I immune sera. The mechanism of killing of serum-sensitive GC is due, in part, to immunoglobulin M antibodies against the asialylated Gal-GlcNAc-R LOS structure (2) which are naturally present in NHS. Additionally, sialylated GC show dramatically reduced invasion of some (43, 46) but not other (13, 44) cultured human epithelial and endothelial cells. There is also a reduced ability of sialylated GC to adhere to and stimulate the oxidative burst in human neutrophils in an opacity-associated (Opa) outer membrane protein-dependent manner (32). Additionally, phagocytic killing of sialylated GC by neutr...
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