Binding Studies on the Neisseria Opa Protein Interaction with Human CEACAM Receptor

Pathogenic Neisseria bacteria, which cause the diseases meningitis and increasingly antibiotic-resistant forms of gonorrhea, induce engulfment into diverse cell types by engaging their outer membrane opacity-associated (Opa) adhesin proteins with the host receptor, carcinoembryonic antigen-related cellular adhesion molecules (CEACAMs). A widely-studied class of CEACAM receptors, CEACAM1, is expressed in most immune cells, and interacts with Opa60, an Opa protein variant. In addition to recognizing Opa60, CEACAM1 binds itself homotypically. N-glycosylation of residues on the CEACAM1 IgV domain (nCEACAM1) has been shown to prevent homodimerization, which is necessary to study the Opa60-nCEACAM1 interaction in vitro. The Opa60 binding interaction with N-glycosylated nCEACAM1 was investigated in vitro using surface plasmon resonance (SPR) spectroscopy. Additionally, binding conditions were optimized in order to improve immobilized Opa60 liposome surface regeneration and to reduce non-specific binding (NSB) to the streptavidin (SA)-coated SPR sensor surface. Significant reduction of NSB was achieved with the addition of 1% BSA to flow buffer. Initial binding studies suggest that a 1:1 steady-state kinetics model describes the wild-type Opa60 and GlcNAc-nCEACAM1 interaction, compared to a limited response from the HV-less (HV-) Opa60 control.