X-ray reflectivity investigations of two-dimensional assemblies of C-cadherins: First steps in structural and functional studies

Cadherins are transmembrane proteins involved in cell adhesion. They play a major role in recognition and adhesion between adjacent cells via calcium dependent interactions. Our studies aim at determining the laws of assembly of Cadherins and locating the adhesive interactions along the proteins, starting from low-resolution structures obtained by X-rays grazing incidence reflectivity. We have realized monolayers of the extracellular fragment of C-cadherin of the frog Xenopus, anchored to nickel chelating lipids at the water surface. From X-ray reflectivity measurements carried out at ESRF, we have elaborated profiles of the electron density of the proteins along their axis with 0.9 nm resolution. We have studied their adhesive behaviour with high and low calcium concentrations and we show an ordering of the protein above 1 mM of calcium. We present an attempt to locate the binding of a short fragment of Cadherin on the full-length protein. The complementarities of our results with those of biochemical studies should enable us to comprehend further cellular adhesion mechanisms.