CD66 receptor specificity exhibited by neisserial Opa variants is controlled by protein determinants in CD66 N-domains

Abstract

Neisseria gonorrhoeae strain MS11 is able to express 11 different opacity (Opa) proteins on its outer surface. A number of these Opa proteins have been shown to function as adhesins through binding of CD66 receptors present on human cells. CD66 antigens, or carcinoembryonic antigen family members, constitute a family of glycoproteins belonging to the immunoglobulin superfamily. Opa variants recognize this class of receptors in a differential manner such that certain Opa variants recognize up to four different CD66 receptors (CD66a, -c, -d, and -e), whereas others recognize only two (CD66a and -e) or none. We explored the basis for this receptor tropism in the present study. Our data show that glycoforms of CD66e and deglycosylated CD66e are recognized by gonococci in an Opa-specific manner. Binding by Opa variants of recombinant N-terminal domains of CD66 receptors expressed in Escherichia coli reflected the adherence specificities of Opa variants to HeLa cells expressing native CD66 molecules. These data indicate that recognition of CD66 receptors by Opa variants is mediated by the protein backbone of the CD66 N-domains. Furthermore, by using chimeric constructs between different CD66 N-domains we identified distinct binding regions on the CD66e N-domain for specific groups of Opa variants, suggesting that the differential recognition of CD66 receptors by Opa variants is dictated by the presence of specific binding regions on the N-domain of the receptor.

Molecular analysis of neisserial Opa protein interactions with the CEA family of receptors: identification of determinants contributing to the differential specificities of binding

“…The fact that Opa proteins recognize CEACAM3 indicates that all elements necessary for binding are present in the conserved N-terminal domain of CEACAM molecules. This premise has also been con®rmed by binding experiments performed using soluble recombinant CEACAM1 and CEACAM5 N-domains (Virji et al, 1996b;Bos et al, 1998). CEACAM8 is not recognized by any Opa protein tested to date, despite the fact that it shares the same domain organization and has about 70% sequence identity with the other CEACAM receptors (i.e.…”

“…However, the level of glycosylation may vary depending upon cell type and differentiation state, and multiple glycoforms of the same protein have even been isolated from a single colonic tumour metastasis (Hefta et al, 1990). In clear contrast to HSPG binding by Opa 50 (Chen et al, 1995;van Putten and Paul, 1995), Bos et al (1998) have recently demonstrated that carbohydrate structures are not involved in Opa binding to the CEACAM receptors. The fact that CEACAM3 lacks any IgC2-like domains (Nagel et al, 1993;Fig.…”

Homophilic adhesion of human CEACAM1 involves N-terminal domain interactions: structural analysis of the binding site

“…50 Heterophilic interactions of the CEACAM1 N-terminal domain with murine corona viruses, H influenzae and Opa proteins of N meningiditis and N gonorrheae also occur on the GFCCЈCЉ face of CEACAM1. 18,[50][51][52][53][54][55][56][57] Amino acids between 34 to 52 in the CCЈ loop region of the murine CEACAM1 N-terminal domain are crucial for murine corona virus interaction. 51 Similarly, amino acids between residues 27 to 42 (particularly the triplet Q27L28F29) and S32, …”

'Small' talk: Opa proteins as mediators of Neisseria–host-cell communication

“…In addition, CEACAM1, CEACAM3 and CEACAM7 genes can be expressed in several splice variants, affecting the number of IgC2 domains or the length and presence of cytoplasmic domains. Although the amino-terminal Ig v -like domain is conserved in all CEACAM family members, and although this domain contains the Opa CEA protein binding site [38,39], CEA-CAM4, CEACAM 7 and CEACAM8 are not recognised by any Opa protein characterised so far [40]. On the basis of Opa CEA -binding and non-binding CEACAM aminoterminal domains, several receptor chimeras and mutants have been constructed to delineate the Opa CEA binding site on the non-glycosylated C'CFG face of the Igdomain fold (reviewed in [41]).…”