Measurement of membrane binding between recoverin, a calcium-myristoyl switch protein, and lipid bilayers by AFM-based force spectroscopy

Myristoyl switch is a feature of several peripheral membrane proteins involved in signal transduction pathways. This unique molecular property is best illustrated by the "Ca2+"-myristoyl switch" of recoverin, which is a Ca2+-binding protein present in retinal rod cells of vertebrates. In this transduction pathway, the Ca2+-myristoyl switch acts as a calcium sensor involved in cell recovery from photoactivation. Ca2+ binding by recoverin induces the extrusion of its myristoyl group to the solvent, which leads to its translocation from cytosol to rod disk membranes. Force spectroscopy, based on atomic force microscope (AFM) technology, was used to determine the extent of membrane binding of recoverin in the absence and presence of calcium, and to quantify this force of binding. An adhesion force of 48 +/- 5 pN was measured between recoverin and supported phospholipid bilayers in the presence of Ca2+. However, no binding was observed in the absence of Ca2+. Experiments with nonmyristoylated recoverin confirmed these observations. Our results are consistent with previously measured extraction forces of lipids from membranes.