Many proteins function in mechanically stressful environments. For example, shear flow in blood vessel may exert a force as high as hundreds of piconewtons on an individual selectin-ligand bond. With such a mechanical force, the receptor (selectin) may deform, thereby altering the conformational match between the receptor and the ligand. Although van der Waals forces, electrostatic and hydrophobic interactions are all important, it is often the 3D geometry local to the binding pocket that dictates the characteristics of the bond between the receptor and the ligand. Good conformational matches lead to strong and long-lasting bonds, whereas poor conformational matches do the converse. it is conceivable that conformational changes in proteins in response to various forces serve as a mechanism for transducing mechanical signals into biochemical responses.