Acidic/IQ motif regulator of calmodulin.
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.
Putkey
John A
JA
Department of Biochemistry and Molecular Biology, University of Texas, Houston Medical School, Houston, Texas 77030. Electronic address: john.putkey@uth.tmc.edu.
Waxham
M Neal
MN
Department of Neurobiology and Anatomy, University of Texas, Houston Medical School, Houston, Texas 77030.
Gaertner
Tara R
TR
Department of Neurobiology and Anatomy, University of Texas, Houston Medical School, Houston, Texas 77030.
Brewer
Kari J
KJ
Department of Biochemistry and Molecular Biology, University of Texas, Houston Medical School, Houston, Texas 77030.
Goldsmith
Michael
M
Department of Biochemistry and Molecular Biology, University of Texas, Houston Medical School, Houston, Texas 77030.
Kubota
Yoshihisa
Y
Department of Neurobiology and Anatomy, University of Texas, Houston Medical School, Houston, Texas 77030.
Kleerekoper
Quinn K
QK
Department of Biochemistry and Molecular Biology, University of Texas, Houston Medical School, Houston, Texas 77030.
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
D000577:Amides; D002147:Calmodulin; D010455:Peptides; D002118:Calcium