Structural basis of the dynamic human CEACAM1 monomer-dimer equilibrium

Abstract

Human (h) carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) function depends upon IgV-mediated homodimerization or heterodimerization with host ligands, including hCEACAM5 and hTIM-3, and a variety of microbial pathogens. However, there is little structural information available on how hCEACAM1 transitions between monomeric and dimeric states which in the latter case is critical for initiating hCEACAM1 activities. We therefore mutated residues within the hCEACAM1 IgV GFCC face including V39, I91, N97 and E99 and examined hCEACAM1 IgV monomer-homodimer exchange using differential scanning fluorimetry, multi-angle light scattering, X-ray crystallography and/or nuclear magnetic resonance. From these studies, we describe hCEACAM1 homodimeric, monomeric and transition states at atomic resolution and its conformational behavior in solution through NMR assignment of the wildtype (WT) hCEACAM1 IgV dimer and N97A monomer. These studies reveal the flexibility of the GFCC face and its important role in governing the formation of hCEACAM1 dimers and potentially heterodimers.

Human CEACAM1 N-domain dimerization is independent from glycan modifications

“…Electron tomography data with soluble rat CEA-CAM1 ectodomains containing all four Ig domains support dimers of the GFCC 0 C 00 interface and show that an additional distinct orientation of the dimer can occur but is a minor population (Klaile et al, 2009). Non-glycosylated CCM1 in solution was reported to have the GFCC 0 C 00 dimer interface (Zhuo et al, 2016), and alanine mutations on the GFCC 0 C 00 dimerization face were shown to increase the monomer population (Gandhi et al, 2021). Collectively, these data suggest the dimer observed in the 4QXW structure is the dominant domain orientation in solution, although this is not conclusive (Zhuo et al, 2016).…”