Engineering the Interactions of Classical Cadherin Cell-Cell Adhesion Proteins

Abstract

Classical cadherins are calcium-dependent cell-cell adhesion proteins that play key roles in the formation and maintenance of tissues. Deficiencies in cadherin adhesion are hallmarks of numerous cancers. In this article, we review recent biophysical studies on the regulation of cadherin structure and adhesion. We begin by reviewing distinct cadherin binding conformations, their biophysical properties, and their response to mechanical stimuli. We then describe biophysical guidelines for engineering Abs that can regulate adhesion by either stabilizing or destabilizing cadherin interactions. Finally, we review molecular mechanisms by which cytoplasmic proteins regulate the conformation of cadherin extracellular regions from the inside out.

Figure 1:. Structure and biomechanics of E-cadherin trans dimers.

(a) Strand-swap dimers formed by the interaction of full length ectodomains of E-cadherin from opposing cell surfaces (green and blue, PDB: 3Q2V). (b) Structure of the outer two domains (EC1–2) forming a strand-swap dimer (PDB: 2O72). Strand-swap dimers are formed by exchanging the N terminal β-strands (residues 1–12 from opposing ectodomains are highlighted in green and blue). (c) X-dimers (PDB: 4ZT1) are formed due to interactions between EC1–2 domains of opposing cadherins. These interactions include hydrogen bonds and a key salt bridge (K14-D138) between loops 11–15 and 135–139 which are highlighted in green and blue. (d) Strand-swap dimers form slip bonds. The lifetime of a slip bond decreases with increasing in pulling force. (e) X-dimers form catch bonds. Catch bonds initially strengthen before weakening beyond a critical pulling force. Panel (d) is adapted from reference (29) while panel (e) is adapted from reference (42).

Figure 2:. Regulating classical cadherin adhesion.

Cadherin adhesion can be regulating either via extracellular binding with antibodies or from the inside-out by cytoplasmic proteins. Activating antibodies 19A11 (magenta, PDB: 6CXY) and 66E8 (cyan, PDB:6VEL) recognize E-cadherin EC1 or EC2 domain (green, PDB: 3Q2V) near the cadherin trans binding sites. Antibody TSP7 (blue, PDB: 5JYL) inhibits P-cadherin adhesion by binding on the EC1 domain while 67G8 (orange) inhibits E-cadherin adhesion by binding on EC5 domain. The intracellular domain of cadherin (green) associates with various signaling molecules, including β-catenin (pink, PDB: 3L6X), p120-catenin (light yellow, PDB: 4R10), α-catenin (red), and vinculin (grey), which eventually link the cadherin cytoplasmic region to F-actin. The structures of α-catenin, vinculin, and E-cadherin intracellular domain were predicted using Alphafold (94). Unless apparent from the crystal structure, all interactions were predicted using Alphafold.