GONOCOCCAL OPACITY - LECTIN-LIKE INTERACTIONS BETWEEN OPA PROTEINS AND LIPOOLIGOSACCHARIDE

Previous evidence from our laboratory suggested that the tight interce llular adhesions between the outer membranes of gonococci displaying t he opacity colony phenotype occurred because Opa proteins expressed on one gonococcus adhered to the lipooligosaccharide (LOS) of the opposi ng bacterium (M. S. Blake, p. 51-66, in G. G. Jackson and H. Thomas, e d., The Pathogenesis of Bacterial Infections, 1985, and M. S. Blake an d E. C. Gotschlich, p. 377-400, in M. Inouye, ed., Bacterial Outer Mem branes 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 t he gonococcal LOS structures that bind Opa proteins (R. T. Lee, Target ed Diagn., Ther. Ser. 4:65-84, 1991). The LOS carbohydrates used in th ese assays were LOS structures purified from pyocin LOS mutants of Nei sseria gonorrhoeae 1291 described by K. C. Dudas and M. A. Apicella (I nfect. Immun. 56:499-504, 1988) and further characterized by C. M. Joh n ct al. (J. Biol. Chem. 266:19303-19311, 1991), Purified gonococcal O pa 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 det ermined indirectly by measuring the concentrations of Opa proteins tha t noncompetitively inhibited 50% of the binding of LOS-specific monocl onal antibodies. This concentration is inversely proportional to the a ffinity of the inhibitor (R. T. Lee, Targeted Diagn. Ther. Ser. 4:65-8 4, 1991). Our data suggest that the gonococcal Opa proteins tested had the highest affinity for the Gal beta 1-4GlcNAc residue present on th e gonococcal lactoneoseries LOS. This affinity was comparable to that reported for the binding of the major hepatic asialoglycoprotein recep tor to glycoconjugates containing terminal galactose and N-acetylgalac tosamine (R. T. Lee, Targeted Diagn. Ther. Ser. 4:65-84, 1991). After sialylation of the lactoneoseries LOS, presumably on the terminal gala ctose residue, the interaction with the Opa proteins was ablated. Ther efore, the gonococcal Opa-LOS and mammalian epithelial cell asialoglyc oprotein receptor-carbohydrate interactions have quite similar specifi cities.