Molecular mechanism for divergent regulation of Cav1.2 Ca2+ channels by calmodulin and Ca2+-binding protein-1.
Ca(2+)-binding protein-1 (CaBP1) and calmodulin (CaM) are highly related Ca(2+)-binding proteins that directly interact with, and yet differentially regulate, voltage-gated Ca(2+) channels. Whereas CaM enhances inactivation of Ca(2+) currents through Ca(v)1.2 (L-type) Ca(2+) channels, CaBP1 completely prevents this process. How CaBP1 and CaM mediate such opposing effects on Ca(v)1.2 inactivation is unknown. Here, we identified molecular determinants in the alpha(1)-subunit of Ca(v)1.2 (alpha(1)1.2) that distinguish the effects of CaBP1 and CaM on inactivation. Although both proteins bind to a well characterized IQ-domain in the cytoplasmic C-terminal domain of alpha(1)1.2, mutations of the IQ-domain that significantly weakened CaM and CaBP1 binding abolished the functional effects of CaM, but not CaBP1. Pulldown binding assays revealed Ca(2+)-independent binding of CaBP1 to the N-terminal domain (NT) of alpha(1)1.2, which was in contrast to Ca(2+)-dependent binding of CaM to this region. Deletion of the NT abolished the effects of CaBP1 in prolonging Ca(v)1.2 Ca(2+) currents, but spared Ca(2+)-dependent inactivation due to CaM. We conclude that the NT and IQ-domains of alpha(1)1.2 mediate functionally distinct interactions with CaBP1 and CaM that promote conformational alterations that either stabilize or inhibit inactivation of Ca(v)1.2.
Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Hong
H
Zhou
Kuai
K
Yu
Kelly L
KL
McCoy
Amy
A
Lee
D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000737:chemistry / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000502:physiology*; D002147:Calmodulin / Q000502:physiology*; D002460:Cell Line; D006801:Humans; D011487:Protein Conformation; D017434:Protein Structure, Tertiary
D020746:Calcium Channels, L-Type; D002135:Calcium-Binding Proteins; D002147:Calmodulin; C419385:L-type calcium channel alpha(1C); C085577:Ca2+-binding protein-1; D002118:Calcium