Structural basis of the dynamic human CEACAM1 monomer-dimer equilibrium

Area of Science:

• Structural biology
• Molecular and cell biology
• Biochemistry

Background:

• Human CEACAM1 (carcinoembryonic antigen-related cell adhesion molecule 1) is a cell adhesion molecule crucial for various biological functions.
• CEACAM1 function relies on homodimerization or heterodimerization via its IgV domain with ligands like CEACAM5, TIM-3, PD-1, and pathogens.
• Limited structural data exists on the monomer-dimer transitions of CEACAM1, a critical step for its activity.

Purpose of the Study:

• To elucidate the structural mechanisms governing human CEACAM1 IgV domain monomer-dimer transitions.
• To characterize the atomic resolution structures of CEACAM1 monomeric, dimeric, and transition states.
• To understand the role of the GFCC' face in CEACAM1 dimerization and ligand interactions.

Main Methods:

• Site-directed mutagenesis of key residues (V39, I91, N97, E99) in the hCEACAM1 IgV domain.
• Differential scanning fluorimetry (DSF) to study protein stability and conformational changes.
• Multi-angle light scattering (MALS) to determine oligomeric states in solution.
• X-ray crystallography and Nuclear Magnetic Resonance (NMR) spectroscopy for atomic-resolution structural determination and dynamics.

Main Results:

• Atomic resolution structures of hCEACAM1 homodimeric, monomeric, and transition states were determined.
• NMR assignment of wildtype (WT) hCEACAM1 IgV dimer and N97A mutant monomer provided insights into conformational behavior in solution.
• The GFCC' face of the IgV domain exhibits flexibility, crucial for regulating dimer formation.
• Mutagenesis studies identified specific residues influencing monomer-homodimer exchange.

Conclusions:

• The study provides the first atomic-resolution description of hCEACAM1 IgV domain monomer-dimer transitions.
• The flexibility of the GFCC' face is a key determinant for hCEACAM1 homodimerization and selective heterodimerization.
• Understanding these structural dynamics is vital for deciphering CEACAM1's role in cellular processes and disease.