Role of the Acylated Amino Terminus of Recoverin in Ca 2+ -Dependent Membrane Interaction

Abstract

Recoverin, a calcium ion (Ca 2+ )-binding protein of vertebrate photoreceptors, binds to photoreceptor membranes when the Ca 2+ concentration is greater than 1 micromolar. This interaction requires a fatty acyl residue covalently linked to the recoverin amino (NH 2 )-terminus. Removal of the acyl residue, either by proteolytic cleavage of the NH 2 -terminus or by production of nonacylated recoverin, prevented recoverin from binding to membranes. The acylated recoverin NH 2 -terminus could be cleaved by trypsin only when Ca 2+ was bound to recoverin. These results suggest that the hydrophobic NH 2 -terminus is constrained in Ca 2+ -free recoverin and liberated by Ca 2+ binding. The hydrophobic acyl moiety of recoverin may interact with the membrane only when recoverin binds Ca 2+ .