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The human pathogens Neisseria meningitidis and Neisseria gonorrhoeae express a family of variable outer membrane opacity-associated (Opa) proteins that recognize multiple human cell surface receptors. Most Opa proteins target the highly conserved N-terminal domain of the CD66 family of adhesion molecules, although a few also interact with heparan sulphate proteoglycans. In this study, we observed that at least two Opa proteins of a N. meningitidis strain C751 have the dual capacity to interact with both receptors. In addition, all three Opa proteins of C751 bind equally well to HeLa cells transfected with cDNA encoding the carcinoembryonic antigen [CEA (CD66e)] subgroup of the CD66 family, but show distinct tropism for CGM1- (CD66d) and NCA (CD66c)-expressing cells. Because the C751 Opa proteins make up distinct structures via the surface-exposed hypervariable domains (HV-1 and HV-2), these combinations appear to be involved in tropism for the distinct CD66 subgroups. To define the determinants of receptor recognition, we used mutant proteins of biliary glycoprotein [BGP (CD66a)] carrying substitutions at several predicted exposed sites in the N-domain and compared their interactions with several Opa proteins of both N. meningitidis and N. gonorrhoeae. The observations applied to the molecular model of the BGP N-domain that we constructed show that the binding of all Opa proteins tested occurs at the non-glycosylated (CFG) face of the molecule and, in general, appears to require Tyr-34 and Ile-91. Further, efficient interaction of distinct Opa proteins depends on different non-adjacent amino acids. In the three-dimensional model, these residues lie in close proximity to Tyr-34 and Ile-91 at the CFG face, making continuous binding domains (adhesiotopes). The epitope of the monoclonal antibody YTH71.3 that inhibits Opa/CD66 interactions was also identified within the Opa adhesiotopes on the N-domain. These studies define the molecular basis that directs the Opa specificity for the CD66 family and the rationale for tropism of the Opa proteins for the CD66 subgroups.

Original publication

DOI

10.1046/j.1365-2958.1999.01620.x

Type

Journal article

Journal

Molecular microbiology

Publication Date

11/1999

Volume

34

Pages

538 - 551

Addresses

Department of Pathology and Microbiology, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK. m.virji@bristol.ac.uk

Keywords

Tumor Cells, Cultured, Humans, Neisseria gonorrhoeae, Neisseria meningitidis, Bacterial Outer Membrane Proteins, Cell Adhesion Molecules, Receptors, Cell Surface, Antigens, Differentiation, Antigens, CD, Antigens, Bacterial, Bacterial Adhesion, Binding Sites, Amino Acid Sequence, Protein Structure, Tertiary, Mutation, Models, Molecular, Molecular Sequence Data, Heparan Sulfate Proteoglycans