Among the different mechanically-driven functions that exist in biology, one of the clearest is adhesion.In the midst of this field, cadherins are one of the most extended proteins in the body, both for cell-cell and same-cell adhesion. They inherit the name from their calcium dependence (calcium-dependent adhesion) and are present from developmental stages in epithelial tissue and synapses, amidst other places. In particular, E-cadherin (epithelial) and N-cadherin (neural) are the most known, and mediate union of different cells by means of a homoproteic interaction.
A remarkable cadherin system is the one bridging stereocilia of ear hair cells. These differ from classical cadherins in several points: firstly, they join parts of the same cell instead of different ones; also the adhesion is mediated by the interaction of two different kinds of cadherins (cadherin 23 y protocadherin 15); and the interaction is well known as a tetramer (a trans dimer of cadherin 23 and another trans dimer of protocadhein 15, interacting in cis).
In the last years, our group has studied the nanomechanics of these proteins, and characterized their unfolding using force spectroscopy both by atomic force microscopy and using molecular dynamics simulations. With these studies we have characterized a new mechanical-resistance element, christened "calcium rivet", as well as the canalization effects of this ion. We have also characterized the differences between classical and ear cadherins, such as the mechanical stability dependence on calcium concentration.