Dissection of NCAD12: Distinctive Characteristics of Domains 1 and 2

The cadherin superfamily of cell surface adhesion molecules have long been recognized for their crucial roles in morphogenesis, and controlled growth and turnover in adult tissues. Neural cadherins (NCAD) are involved in the cell to cell adhesion of neural tissue. Neural cadherin molecules share a common structure with the members of its superfamily including an amino terminal extracellular region, a transmembrane region and a carboxyl-terminal cytoplasmic region. It contains five folded domains in its extracellular region that are seven strand B-barrel modules of the immunoglobulin type. These modular domains are then connected by a seven amino acid sequence known as linker regions. It has been reported that calcium binding and Domains 1 and 2 are essential to adhesion. Previous studies of Epithelial cadherin (ECAD) have characterized the stability as a function of temperature and denaturant concentration. Here, we report studies of the component modules of dissected NCAD 12: the extracellular domains individually (NCAD 1 and NCAD 2) and the two-Domain construct NCAD 12. Ultra violet (UV) spectra of all NCAD constructs were used to determine stock concentrations and molar extinctions coefficients. Thermal denaturation was monitored via circular dicroism (CD) in the presence and absence of calcium. Data showed a stable NCAD 1 with an uncharacteristically high melting temperature. NCAD 2 was very similar to ECAD 2 in that the core domain was quite stable and it is destabilized by the adjacent linker segments. Domain 2 constructs were stabilized by calcium. The primary melting transition for the two-Domain construct, NCAD 12, was similar to the melting transition for NCAD 2, indicating that the stability of the construct is dominated by that of Domain 2. However, NCAD 12 also showed the high temperature melting transition as seen for constructs containing Domain 1. This second transition makes data analysis problematic. Our studies indicate that formation of this “stable” species is reversible and independent of protein and calcium concentration