Extraordinary Stability of Domain 1 of Neural-Cadherin

Abstract

Cadherins are transmembrane proteins responsible for calcium dependent cell-cell adhesion. Classical cadherins have a common structure with five extracellular domains, connected by a 7-residue sequence linker region. Cadherins mediate adhesion via Adherens Junctions by forming a strand-swapped structure between identical protomers from apposing cells. The adhesive interface has been characterized structurally, and biophysical studies have been used to elucidate the forces that stabilize the strand-swapped structure. Upon calcium binding, the swapping of the N-terminal strands between protomers allows for the symmetrical docking of a tryptophan residue required for adhesion. Fundamental questions still remain regarding the striking difference in the calcium-dependent kinetics of dimerization between N- and E-cadherin. This study compares the first extracellular domain of N-cadherin (NCAD1) and E-cadherin (ECAD1). With NCAD1, the binding pocket for calcium is not complete, so dimerization was not expected. However, we observed a dimeric form that was not in exchange with monomer. This dimer was reversibly converted to monomer by heating the protein. Noticeably, NCAD1 was found to unfold at an uncharacteristically high temperature. Results for NCAD1 construct were similar to results for domain 1 in studies of the two-domain construct, NCAD12. Similar studies of ECAD1 show that it is significantly lower stability. In summary, our results indicate that the difference in kinetics of dimerization may be due to a difference in the intrinsic stability of domain 1.GAANN P200A120046