title: Amino acid residues of S-modulin responsible for interaction with rhodopsin kinase.
abstract: S-modulin in frog or its bovine homologue, recoverin, is a 23-kDa EF-hand Ca(2+)-binding protein found in rod photoreceptors. The Ca(2+)-bound form of S-modulin binds to rhodopsin kinase (Rk) and inhibits its activity. Through this regulation, S-modulin is thought to modulate the light sensitivity of a rod. In the present study, we tried to identify the interaction site of the Ca(2+)-bound form of S-modulin to Rk. First, we mapped roughly the interaction regions by using partial peptides of S-modulin. The result suggested that a specific region near the amino terminus is the interaction site of S-modulin. We then identified the essential amino acid residues in this region by using S-modulin mutant proteins: four amino acid residues (Phe(22), Glu(26), Phe(55), and Thr(92)) were suggested to interact with Rk. These residues are located in a small closed pocket in the Ca(2+)-free, inactive form of S-modulin, but exposed to the surface of the molecule in the Ca(2+)-bound, active form of S-modulin. Two additional amino acid residues (Tyr(108) and Arg(150)) were found to be crucial for the Ca(2+)-dependent conformational changes of S-modulin.
authors.affiliation: Department of Biology, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Tachibanaki
authors.forename: K
authors.initials: K
authors.lastname: Nanda
authors.forename: K
authors.initials: K
authors.lastname: Sasaki
authors.forename: K
authors.initials: K
authors.lastname: Ozaki
authors.forename: S
authors.initials: S
authors.lastname: Kawamura
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002417:Cattle; D002942:Circular Dichroism; D005136:Eye Proteins; D051606:G-Protein-Coupled Receptor Kinase 1; D051597:Hippocalcin; D008074:Lipoproteins; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009419:Nerve Tissue Proteins; D011487:Protein Conformation; D011494:Protein Kinases / Q000737:chemistry / Q000378:metabolism*; D051603:Recoverin; D013379:Substrate Specificity
chemical_list: D000596:Amino Acids; D002135:Calcium-Binding Proteins; D005136:Eye Proteins; D008074:Lipoproteins; D009419:Nerve Tissue Proteins; D051603:Recoverin; D051597:Hippocalcin; D011494:Protein Kinases; D051606:G-Protein-Coupled Receptor Kinase 1