Discrete interactions in cell adhesion measured by single-molecule force spectroscopy.

Cell-cell adhesion mediated by specific cell-surface molecules is essential for multicellular development. Here we quantify de-adhesion forces at the resolution of individual cell-adhesion molecules, by controlling the interactions between single cells and combining single-molecule force spectroscopy with genetic manipulation. Our measurements are focused on a glycoprotein, contact site A (csA), as a prototype of cell-adhesion proteins. csA is expressed in aggregating cells of Dictyostelium discoideum, which are engaged in development of a multicellular organism. Adhesion between two adjacent cell surfaces involves discrete interactions characterized by an unbinding force of 23 +/- 8 pN, measured at a rupture rate of 2.5 +/- 0.5 microm s-1.