Rem GTPase interacts with the proximal CaV1.2 C-terminus and modulates calcium-dependent channel inactivation.
The Rem, Rem2, Rad, and Gem/Kir (RGK) GTPases, comprise a subfamily of small Ras-related GTP-binding proteins, and have been shown to potently inhibit high voltage-activated Ca(2+) channel current following overexpression. Although the molecular mechanisms underlying RGK-mediated Ca(2+) channel regulation remains controversial, recent studies suggest that RGK proteins inhibit Ca(2+) channel currents at the plasma membrane in part by interactions with accessory channel β subunits. In this paper, we extend our understanding of the molecular determinants required for RGK-mediated channel regulation by demonstrating a direct interaction between Rem and the proximal C-terminus of Ca(V)1.2 (PCT), including the CB/IQ domain known to contribute to Ca(2+)/calmodulin (CaM)-mediated channel regulation. The Rem2 and Rad GTPases display similar patterns of PCT binding, suggesting that the Ca(V)1.2 C-terminus represents a common binding partner for all RGK proteins. In vitro Rem:PCT binding is disrupted by Ca(2+)/CaM, and this effect is not due to Ca(2+)/CaM binding to the Rem C-terminus. In addition, co-overexpression of CaM partially relieves Rem-mediated L-type Ca(2+) channel inhibition and slows the kinetics of Ca(2+)-dependent channel inactivation. Taken together, these results suggest that the association of Rem with the PCT represents a crucial molecular determinant in RGK-mediated Ca(2+) channel regulation and that the physiological function of the RGK GTPases must be re-evaluated. Rather than serving as endogenous inhibitors of Ca(2+) channel activity, these studies indicate that RGK proteins may play a more nuanced role, regulating Ca(2+) currents via modulation of Ca(2+)/CaM-mediated channel inactivation kinetics.
Pang
Chunyan
C
Department of Molecular and Cellular Biochemistry and Physiology, University of Kentucky College of Medicine, Lexington, USA.
Crump
Shawn M
SM
Jin
Ling
L
Correll
Robert N
RN
Finlin
Brian S
BS
Satin
Jonathan
J
Andres
Douglas A
DA
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D002147:Calmodulin; D007700:Kinetics; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism* / Q000502:physiology; D018631:ras Proteins / Q000378:metabolism
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D002147:Calmodulin; C108135:Rem protein, mouse; C490030:Rrad protein, mouse; D020559:Monomeric GTP-Binding Proteins; C517391:Rem2 protein, mouse; D018631:ras Proteins; D002118:Calcium
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