Intrinsically disordered PEP-19 confers unique dynamic properties to apo and calcium calmodulin.

PEP-19 (Purkinje cell protein 4) is an intrinsically disordered protein with an IQ calmodulin (CaM) binding motif. Expression of PEP-19 was recently shown to protect cells from apoptosis and cell death due to Ca(2+) overload. Our initial studies showed that PEP-19 causes novel and dramatic increases in the rates of association of Ca(2+) with and dissociation of Ca(2+) from the C-domain of CaM.

Intra- and interdomain effects due to mutation of calcium-binding sites in calmodulin.

The IQ-motif protein PEP-19, binds to the C-domain of calmodulin (CaM) with significantly different k(on) and k(off) rates in the presence and absence of Ca(2+), which could play a role in defining the levels of free CaM during Ca(2+) transients. The initial goal of the current study was to determine whether Ca(2+) binding to sites III or IV in the C-domain of CaM was responsible for affecting the kinetics of binding PEP-19. EF-hand Ca(2+)-binding sites were selectively inactivated by the common strategy of changing Asp to Ala at the X-coordination position.

PEP-19, an intrinsically disordered regulator of calmodulin signaling.

PEP-19 is a small calmodulin (CaM)-binding protein that greatly increases the rates of association and dissociation of Ca(2+) from the C-domain of CaM, an effect that is mediated by an acidic/IQ sequence in PEP-19. We show here using NMR that PEP-19 is an intrinsically disordered protein, but with residual structure localized to its acidic/IQ motif. We also show that the k(on) and k(off) rates for binding PEP-19 to apo-CaM are at least 50-fold slower than for binding to Ca(2+)-CaM.

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.

Sites on calmodulin that interact with the C-terminal tail of Cav1.2 channel.

Two fragments of the C-terminal tail of the alpha(1) subunit (CT1, amino acids 1538-1692 and CT2, amino acids 1596-1692) of human cardiac L-type calcium channel (Ca(V)1.2) have been expressed, refolded, and purified. A single Ca(2+)-calmodulin binds to each fragment, and this interaction with Ca(2+)-calmodulin is required for proper folding of the fragment.