Background: PEP-19 modulates the kinetics of Ca2+ binding to CaM. Results: An acidic region in PEP-19 binds Ca2+ and is essential for both modulating Ca2+ binding to CaM and sensitizing cells to ATP-induced Ca2+ release. Conclusion: Simply binding to CaM is not sufficient to account for the biological activities of PEP-19. Significance: Regulating ligand-induced Ca2+ release gives PEP-19 the potential to broadly affect cell signaling. PEP-19 is a small, intrinsically disordered protein that binds to the C-domain of calmodulin (CaM) via an IQ motif and tunes its Ca2+ binding properties via an acidic sequence. We show here that the acidic sequence of PEP-19 has intrinsic Ca2+ binding activity, which may modulate Ca2+ binding to CaM by stabilizing an initial Ca2+-CaM complex or by electrostatically steering Ca 2+ to and from CaM. Because PEP-19 is expressed in cells that exhibit highly active Ca2+ dynamics, we tested the hypothesis that it influences ligand-dependent Ca2+release.We show that PEP-19 increases the sensitivity of HeLa cells to ATPinduced Ca2+ release to greatly increase the percentage of cells responding to sub-saturating doses of ATP and increases the frequency of Ca2+ oscillations. Mutations in the acidic sequence of PEP-19 that inhibit or prevent it from modulating Ca2+ binding to CaM greatly inhibit its effect on ATP-induced Ca2+ release. Thus, this cellular effect of PEP-19 does not depend simply on binding toCaMvia the IQ motif but requires its acidic metal binding domain. Tuning the activities of Ca2+ 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.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cell Biology