title: The calmodulin regulator protein, PEP-19, sensitizes ATP-induced Ca2+ release.
abstract: PEP-19 is a small, intrinsically disordered protein that binds to the C-domain of calmodulin (CaM) via an IQ motif and tunes its Ca(2+) binding properties via an acidic sequence. We show here that the acidic sequence of PEP-19 has intrinsic Ca(2+) binding activity, which may modulate Ca(2+) binding to CaM by stabilizing an initial Ca(2+)-CaM complex or by electrostatically steering Ca(2+) to and from CaM. Because PEP-19 is expressed in cells that exhibit highly active Ca(2+) dynamics, we tested the hypothesis that it influences ligand-dependent Ca(2+) release. We show that PEP-19 increases the sensitivity of HeLa cells to ATP-induced Ca(2+) release to greatly increase the percentage of cells responding to sub-saturating doses of ATP and increases the frequency of Ca(2+) oscillations. Mutations in the acidic sequence of PEP-19 that inhibit or prevent it from modulating Ca(2+) binding to CaM greatly inhibit its effect on ATP-induced Ca(2+) release. Thus, this cellular effect of PEP-19 does not depend simply on binding to CaM via the IQ motif but requires its acidic metal binding domain. Tuning the activities of Ca(2+) mobilization pathways places PEP-19 at the top of CaM signaling cascades, with great potential to exert broad effects on downstream CaM targets, thus expanding the biological significance of this small regulator of CaM signaling.
authors.affiliation: Department of Biochemistry and Molecular Biology and Structural Biology Imaging Center, University of Texas Medical School, Houston, Texas 77030, USA.
authors.forename: Xu
authors.initials: X
authors.lastname: Wang
authors.forename: Liang Wen
authors.initials: LW
authors.lastname: Xiong
authors.forename: Amina
authors.initials: A
authors.lastname: El Ayadi
authors.forename: Darren
authors.initials: D
authors.lastname: Boehning
authors.forename: John A
authors.initials: JA
authors.lastname: Putkey
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D020816:Amino Acid Motifs; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002147:Calmodulin / Q000737:chemistry / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008024:Ligands; D057054:Molecular Imaging; D008969:Molecular Sequence Data; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D055672:Static Electricity; D014162:Transfection
chemical_list: D002147:Calmodulin; D008024:Ligands; D009419:Nerve Tissue Proteins; C050394:PCP4 protein, human; D000255:Adenosine Triphosphate; D002118:Calcium