title: Acidic/IQ motif regulator of calmodulin.
abstract: The small IQ motif proteins PEP-19 (62 amino acids) and RC3 (78 amino acids) greatly accelerate the rates of Ca(2+) binding to sites III and IV in the C-domain of calmodulin (CaM). We show here that PEP-19 decreases the degree of cooperativity of Ca(2+) binding to sites III and IV, and we present a model showing that this could increase Ca(2+) binding rate constants. Comparative sequence analysis showed that residues 28 to 58 from PEP-19 are conserved in other proteins. This region includes the IQ motif (amino acids 39-62), and an adjacent acidic cluster of amino acids (amino acids 28-40). A synthetic peptide spanning residues 28-62 faithfully mimics intact PEP-19 with respect to increasing the rates of Ca(2+) association and dissociation, as well as binding preferentially to the C-domain of CaM. In contrast, a peptide encoding only the core IQ motif does not modulate Ca(2+) binding, and binds to multiple sites on CaM. A peptide that includes only the acidic region does not bind to CaM. These results show that PEP-19 has a novel acidic/IQ CaM regulatory motif in which the IQ sequence provides a targeting function that allows binding of PEP-19 to CaM, whereas the acidic residues modify the nature of this interaction, and are essential for modulating Ca(2+) binding to the C-domain of CaM.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Texas, Houston Medical School, Houston, Texas 77030. Electronic address: john.putkey@uth.tmc.edu.
authors.forename: John A
authors.initials: JA
authors.lastname: Putkey
authors.affiliation: Department of Neurobiology and Anatomy, University of Texas, Houston Medical School, Houston, Texas 77030.
authors.forename: M Neal
authors.initials: MN
authors.lastname: Waxham
authors.affiliation: Department of Neurobiology and Anatomy, University of Texas, Houston Medical School, Houston, Texas 77030.
authors.forename: Tara R
authors.initials: TR
authors.lastname: Gaertner
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Texas, Houston Medical School, Houston, Texas 77030.
authors.forename: Kari J
authors.initials: KJ
authors.lastname: Brewer
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Texas, Houston Medical School, Houston, Texas 77030.
authors.forename: Michael
authors.initials: M
authors.lastname: Goldsmith
authors.affiliation: Department of Neurobiology and Anatomy, University of Texas, Houston Medical School, Houston, Texas 77030.
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Kubota
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Texas, Houston Medical School, Houston, Texas 77030.
authors.forename: Quinn K
authors.initials: QK
authors.lastname: Kleerekoper
mesh_terms: D000577:Amides; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000737:chemistry / Q000378:metabolism*; D016384:Consensus Sequence; D007700:Kinetics; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D025941:Protein Interaction Mapping; D016415:Sequence Alignment
chemical_list: D000577:Amides; D002147:Calmodulin; D010455:Peptides; D002118:Calcium