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

Abstract

SummaryThe carcinoembryonic antigen (CEA) gene family members, CEACAM1, CEACAM3, CEACAM5 and CEA-CAM6, are bound by the Opa outer membrane proteins of pathogenic Neisseria spp., whereas CEACAM8 is not. In this study, we demonstrate that the closely related CEACAM4 and CEACAM7, which are also members of the CEA family, are not Opa receptors. We exploited the high conservation between CEACAM6 and CEACAM8 to generate an extensive set of chimeric receptors in order to delineate the sequences necessary for Opa binding. Using a transfection-based infection system, we showed that binding of Opa 52 involves residues 27±42, which are predicted to form b-strand C and short loops adjacent to it, and residues lying between amino acids 60 and 108 in the amino-terminal domain. The replacement of residues 27±29 in CEACAM6 with the CEACAM1 or CEACAM5 sequences generated recombinant CEA-CAM6 receptors that are bound by CEACAM1/CEA-CAM5-speci®c Opa variants. Together, our data demonstrate that Opa proteins bind to residues exposed on the GFCC 8 face of the N-terminal domain of CEACAM receptors, and identify an amino acid triplet sequence that is responsible for the differential binding of Opa proteins to CEACAM1, CEACAM5 and CEACAM6.

Two Variable Regions in Carcinoembryonic Antigen-related Cell Adhesion Molecule1 N-terminal Domains Located in or Next to Monoclonal Antibody and Adhesion Epitopes Show Evidence of Recombination in Rat but Not in Human

“…However, the close match of its Ndomain to CEACAM1 makes it highly likely that the CEACAM3 N-domain has cell adhesion activity, a supposition supported by its ability to bind Neisseria gonorrhoeae via its opa receptors (72). Although human CEACAM8, a neutrophil CAM in the low similarity group (73%), retains adhesive activity, it adhesion partners are limited to CEACAM6, a widely expressed neutrophil CAM that binds to human CEACAM1, -5, -8 (73), opa proteins (74), and itself. In contrast, CEACAM7 and CEACAM4, with similarities of 64 and 58%, cannot bind opa receptors (74) and have no documented cell-cell adhesion activity.…”

“…Although human CEACAM8, a neutrophil CAM in the low similarity group (73%), retains adhesive activity, it adhesion partners are limited to CEACAM6, a widely expressed neutrophil CAM that binds to human CEACAM1, -5, -8 (73), opa proteins (74), and itself. In contrast, CEACAM7 and CEACAM4, with similarities of 64 and 58%, cannot bind opa receptors (74) and have no documented cell-cell adhesion activity.…”

CEACAM1 Dynamics during Neisseria gonorrhoeae Suppression of CD4+ T Lymphocyte Activation

“…23,24). Individual Opa variants are able to bind to the conserved N-terminal domains of CEACAM1, CEACAM3, CEACAM5, and/or CEACAM6 via specific proteinprotein interactions (25)(26)(27).…”

'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]).…”