Role of the acylated amino terminus of recoverin in Ca²⁺-dependent membrane interaction

Recoverin, a calcium ion (Ca²⁺)-binding protein of vertebrate photoreceptors, binds to photoreceptor membranes when the Ca²⁺ concentration is greater than 1 micromolar. This interaction requires a fatty acyl residue covalently linked to the recoverin amino (NH₂)-terminus. Removal of the acyl residue, either by proteolytic cleavage of the NH₂-terminus or by production of nonacylated recoverin, prevented recoverin from binding to membranes. The acylated recoverin NH₂-terminus could be cleaved by trypsin only when Ca²⁺ was bound to recoverin. These results suggest that the hydrophobic NH₂-terminus is constrained in Ca²⁺-free recoverin and liberated by Ca²⁺ binding. The hydrophobic acyl moiety of recoverin may interact with the membrane only when recoverin binds Ca²⁺.