Calcium-myristoyl protein switch.
Recoverin, a recently discovered member of the EF-hand superfamily of Ca(2+)-binding proteins, serves as a Ca2+ sensor in vision. The amino terminus of the protein from retinal rod cells contains a covalently attached myristoyl or related N-acyl group. We report here studies of unmyristoylated and myristoylated recombinant recoverin designed to delineate the biological role of this hydrophobic unit. Ca2+ induces the binding of both the unmyristoylated and myristoylated proteins to phenyl-agarose, a hydrophobic support. Binding was half-maximal at 1.1 and 1.0 microM Ca2+, respectively. The Hill coefficients of 1.8 and 1.7, respectively, indicate that binding was cooperative. In contrast, Ca2+ induced the binding of myristoylated but not of unmyristoylated recoverin to rod outer segment membranes. Binding to these membranes was half-maximal at 2.1 microM Ca2+, and the Hill coefficient was 2.4. Likewise, myristoylated but not unmyristoylated recoverin exhibited Ca(2+)-induced binding to phosphatidylcholine vesicles. These findings suggest that the binding of Ca2+ to recoverin has two effects: (i) hydrophobic surfaces are exposed, allowing the protein to interact with complementary nonpolar sites, such as the aromatic rings of phenyl-agarose; and (ii) the myristoyl group is extruded, enabling recoverin to insert into a lipid bilayer membrane. The myristoyl group is likely to be an active participant in Ca2+ signaling by recoverin and related EF-hand proteins such as visinin and neurocalcin.
Zozulya
S
S
Department of Cell Biology, Stanford University School of Medicine, CA 94305.
Stryer
L
L
D000595:Amino Acid Sequence; D000818:Animals; D000951:Antigens, Neoplasm / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002417:Cattle; D005136:Eye Proteins; D051597:Hippocalcin; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D008074:Lipoproteins; D008081:Liposomes; D008969:Molecular Sequence Data; D009226:Myristates / Q000378:metabolism*; D009419:Nerve Tissue Proteins; D017368:Protein Prenylation; D011994:Recombinant Proteins / Q000378:metabolism; D051603:Recoverin; D012374:Rod Cell Outer Segment / Q000378:metabolism*; D016415:Sequence Alignment; D015398:Signal Transduction; D013329:Structure-Activity Relationship
D000951:Antigens, Neoplasm; D002135:Calcium-Binding Proteins; D005136:Eye Proteins; D008074:Lipoproteins; D008081:Liposomes; D009226:Myristates; D009419:Nerve Tissue Proteins; D011994:Recombinant Proteins; D051603:Recoverin; D051597:Hippocalcin; D002118:Calcium