Affinity of Trans-interacting VE-cadherin Determined by Atomic Force Microscopy

Vascular endothelial cells form a cellular barrier on the inner surface of blood vessels. Cells adhere to each other by the calcium dependent adhesion molecule VE-cadherin. Dissociation and reassociation of VE-cadherin bonds during inflammatory gap formation or transmigration of leukocytes and tumor cells requires regulation of extracellular binding. In the present study we show by single molecule atomic force microscopy that the interaction time needed for half maximal probability of binding is 0.08 s and the on-rate constant kon ∼︁ 10 4 M —1 s —1. The off-rate constant has been previously shown by our laboratory to be koff 0 ∼︁ 1.8 s —1 . Thus, extracellular trans-interaction of VE-cadherin has a dissociation constant of approximately 2 ⋅ 10 —4 M. This rather low dissociation constant implies a transmembrane cooperative linkage mechanism by which the number of extracellular trans-interacting cadherins may be significantly modulated by the degree of cytoskeletal tethering of their cytoplasmic domains.