Neisserial Opa Protein–CEACAM Interactions: Competition for Receptors as a Means of Bacterial Invasion and Pathogenesis

Abstract

Carcino-embryonic antigen-like cellular adhesion molecules (CEACAMs), members of the immunoglobulin superfamily, are responsible for cell-cell interactions and cellular signaling events. Extracellular interactions with CEACAMs have the potential to induce phagocytosis, as is the case with pathogenic Neisseria bacteria. Pathogenic Neisseria species express opacity associated (Opa) proteins, which interact with a subset of CEACAMs on human cells, and initiate the engulfment of the bacterium. We demonstrate that recombinant Opa proteins reconstituted into liposomes retain the ability to recognize and interact with CEACAMs in vitro, but do not maintain receptor specificity compared to Opa proteins natively expressed by Neisseria gonorrhoeae. We report that two Opa proteins interact with CEACAMs with nanomolar affinity and we hypothesize that this high affinity is necessary to compete with the native CEACAM homo- and heterotypic interactions in the host. Understanding the mechanisms of Opa protein-receptor recognition and engulfment enhances understanding of Neisserial pathogenesis. Additionally, these mechanisms provide insight into how human cells that are typically non-phagocytic can utilize CEACAM receptors to internalize exogenous matter, with implications for the targeted delivery of therapeutics and development of imaging agents.

Imaging Flow Cytometry Analysis of CEACAM Binding to Opa‐Expressing Neisseria gonorrhoeae

“…2). Our results generally correspond to the selectivity of CEACAM-dependent binding of these particular Opa + Gc reported by us (23) and others (10,14,17,21,23,32,33,36,37). Moreover, we found that OpaD+ Gc interacts with CEACAM5, an epithelial CEACAM, which agrees with our observation that OpaD+ Gc binds avidly to epithelial cells (38).…”

“…4a). Similarly, OpaD+ (23) and Opa60+ Gc (10,17,23) were reported Figures 1 and 2, using the concentration of each GST-N-CEACAM determined for OpaD+ Gc in Figure 3. Opaless served as a negative control for background AF488+ fluorescence on bacteria and was used as comparison for statistical significance.…”

Temporal upregulation of host surface receptors provides a window of opportunity for bacterial adhesion and disease

“…Colony opacity-associated (Opa) protein and opacity class 5 protein, Opc, are outer membrane proteins that mediate meningococcal adhesion to CEACAM-1, heparan sulfate proteoglycan (HSPG) and integrins via the extracellular matrix proteins fibronectin and vitronectin [70,71]. Meningococci have been shown to trigger expression of the CEA-CAM-1 receptor on primary endothelial cells via NFkB activation, which increases Opa/CEACAM-1-specific bacterial binding and internalization [72].…”

“…Also, selective FimH-binding mannosides have been indicated in preventing UTIs in a preclinical murine model [106]. In vitro studies have found that anti-CEACAM antibodies block the adhesion of M. catarrhalis, N. meningitidis and NTHi to airway epithelial cells [39,71,107]. Also, NTHi adherence to A549 alveolar epithelial cells in vitro was shown to be inhibited in a dose-dependent manner with increasing concentrations of anti-ICAM-1 monoclonal antibodies [52].…”

Refinement of Highly Flexible Protein Structures using Simulation‐Guided Spectroscopy

“…DEER data were acquired using label pairs selected via both mRMR and traditional structure‐based selection, and we assessed the relative utility of each method in refining the ensemble. The long, flexible loops of Opa 60 are both critical for function, and challenging for previous DEER pair selection methods. In contrast to FhuA or OprG, no structural or functional data provide strong guidance on which residues are responsible for function, in this case receptor engagement.…”