SEQUESTRATION OF THE MEMBRANE-TARGETING MYRISTOYL GROUP OF RECOVERIN IN THE CALCIUM-FREE STATE

RECOVERIN, a retinal calcium-binding protein of relative molecular mass (M(r)) 23K, participates In the recovery phase of visual excitation and in adaptation to background light(1-3) The Ca2+-bound form of recoverin prolongs the photoresponse(4), probably by blocking phosphorylation of photoexcited rhodopsin. Retinal recoverin contains a covalently attached myristoyl group or related acyl group at its amino terminus(6) and two Ca2+-binding sites(7). Ca2+ binding to myristoylated, but not unmyristoylated, recoverin induces its translocation to bilayer membranes, indicating that the myristoyl group is essential to the read-out of calcium signals (calcium-myristoyl switch)(8,9). Here we present the solution structure of Ca2+-free, myristoylated recombinant recoverin obtained by heteronuclear multidimensional NMR spectroscopy. The myristoyl group is sequestered in a deep hydrophobic pocket formed by many aromatic and other hydrophobic residues from five flanking helices.