Gonococcal opacity: lectin-like interactions between Opa proteins and lipooligosaccharide.

Previous evidence from our laboratory suggested that the tight intercellular adhesions between the outer membranes of gonococci displaying the opacity colony phenotype occurred because Opa proteins expressed on one gonococcus adhered to the lipooligosaccharide (LOS) of the opposing bacterium (M.S. Blake, p. 51-66, in G. G. Jackson and H. Thomas, ed., The Pathogenesis of Bacterial Infections, 1985, and M. S. Blake and E. C. Gotschlich, p. 377-400, in M. Inouye, ed., Bacterial Outer Membranes as Model Systems, 1986). A noncompetitive inhibition assay used previously to determine the carbohydrate structures recognized by the major hepatic asialoglycoprotein receptor was modified to determine the gonococcal LOS structures that bind Opa proteins (R. T. Lee, Targeted Diagn. Ther. Ser. 4:65-84, 1991). The LOS carbohydrates used in these assays were LOS structures purified from pyocin LOS mutants of Neisseria gonorrhoeae 1291 described by K. C. Dudas and M. A. Apicella (Infect. Immun. 56:499-504, 1988) and further characterized by C. M. John et al. (J. Biol. Chem. 266:19303-19311, 1991). Purified gonococcal Opa proteins were incubated with each of the parent and mutant LOS, and the amount of binding of Opa proteins was measured by a direct enzyme-linked immunosorbent assay using the Opa-specific monoclonal antibody 4B12. The affinities of the Opa proteins for each of the LOS were determined indirectly by measuring the concentrations of Opa proteins that noncompetitively inhibited 50% of the binding of LOS-specific monoclonal antibodies. This concentration is inversely proportional to the affinity of the inhibitor (R. T. Lee, Targeted Diagn. Ther. Ser. 4:65-84, 1991). Our data suggest that the gonococcal Opa proteins tested had the highest affinity for the Gal beta 1-4GlcNAc residue present on the gonococcal lactoneoseries LOS. This affinity was comparable to that reported for the binding of the major hepatic asialoglycoprotein receptor to glycoconjugates containing terminal galactose and N-acetylgalactosamine (R. T. Lee, Targeted Diagn. Ther. Ser. 4:65-84, 1991). After sialylation of the lactoneoseries LOS, presumably on the terminal galactose residue, the interaction with the Opa proteins was ablated. Therefore, the gonococcal Opa-LOS and mammalian epithelial cell asialoglycoprotein receptor-carbohydrate interactions have quite similar specificities.