Phosphatidylserine Allows Observation of the Calcium-Myristoyl Switch of Recoverin and Its Preferential Binding

Recoverin undergoes a calcium myristoyl switch during visual photo-transduction. Indeed, calcium binding by recoverin results in the extrusion of its myristoyl group, which allows its membrane binding. However, the contribution of particular lipids and of specific amino acids of recoverin in its membrane binding has not yet been demonstrated. In the present work, the affinity of recoverin for the negatively charged phosphatidylserine has been clearly shown to be governed by a cluster of positively charged residues located in its N-terminal segment. Moreover, the calcium myristoyl switch of recoverin was only observed upon binding onto monolayers of phosphatidylserine and not in the case of other anionic phospholipids. Fluorescence microscopy experiments with mixed lipid monolayers allowed confirmation of the specific binding of myristoylated recoverin to phosphatidylserine, whereas the extent of penetration of recoverin in phosphatidylseiine monolayers was estimated by ellipsometry. A model has thus been proposed for the membrane binding of myristoylated recoverin in the presence of calcium. (AU)