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

RECOVERIN, a retinal calcium-binding protein of relative molecular mas s (M(r)) 23K, participates In the recovery phase of visual excitation and in adaptation to background light(1-3) The Ca2+-bound form of reco verin prolongs the photoresponse(4), probably by blocking phosphorylat ion 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 n ot unmyristoylated, recoverin induces its translocation to bilayer mem branes, indicating that the myristoyl group is essential to the read-o ut of calcium signals (calcium-myristoyl switch)(8,9). Here we present the solution structure of Ca2+-free, myristoylated recombinant recove rin obtained by heteronuclear multidimensional NMR spectroscopy. The m yristoyl group is sequestered in a deep hydrophobic pocket formed by m any aromatic and other hydrophobic residues from five flanking helices .