Interactions of calmodulin with two peptides derived from the C-terminal cytoplasmic domain of the Ca(v)1.2 Ca2+ channel provide evidence for a molecular switch involved in Ca2+-induced inactivation
J. Mouton et al., Interactions of calmodulin with two peptides derived from the C-terminal cytoplasmic domain of the Ca(v)1.2 Ca2+ channel provide evidence for a molecular switch involved in Ca2+-induced inactivation, J BIOL CHEM, 276(25), 2001, pp. 22359-22367
When opened by depolarization, L-type calcium channels are rapidly inactiva
ted by the elevation of Ca2+ concentration on the cytoplasmic side, Recent
studies have shown that the interaction of calmodulin with the proximal par
t of the cytoplasmic C-terminal tail of the channel plays a prominent role
in this modulation, Two motifs interacting with calmodulin in a Ca2+-depend
ent manner have been described: the IQ sequence and more recently the neigh
boring CB sequence. Here, using synthetic peptides and fusion proteins deri
ved from the Ca(v)1.2 channel combined with biochemical techniques, we show
that these two peptides are the only motifs of the cytoplasmic tail suscep
tible to interact with calmodulin, We determined the K-d of the CB interact
ion with calmodulin to be 12 nM, i.e, below the K-d of IQ-calmodulin, there
by precluding a competitive displacement of CB by IQ in the presence of Ca2
+. In place, we demonstrated that a ternary complex is formed at high Ca2concentration, provided that calmodulin and the peptides are initially allo
wed to interact at a low Ca2+ concentration. These results provide evidence
that CB and IQ motifs interacting together with calmodulin constitute a mi
nimal molecular switch leading to Ca2+-induced inactivation. In addition, w
e suggest that they could also be the tethering site of calmodulin.