Browsing by Author "Simms, Brett Alan"

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    N-terminal Regulation of L-type Calcium Channel Expression, Function and Trafficking
    (2014-09-24) Simms, Brett Alan; Zamponi, Gerald
    The L-type voltage-gated calcium channel Cav1.2 is important for excitation-contraction coupling in the heart, as well as CREB mediated transcription and fear conditioned learning. The ubiquitous calcium binding protein calmodulin (CaM) and its associated kinase, calmodulin dependent kinase II (CaMKII), are known to modulate calcium-dependent inactivation (CDI) and calcium dependent facilitation (CDF) of voltage-gated calcium channels (VGCCs), respectively. CDI functions to limit the amount of calcium entering through Cav1.2 channels during prolonged or repetitive membrane depolarizations, whereas a facilitative role for CaMKII can be uncovered by mutating the C-terminal PreIQ-IQ region. Here we identify a CaM interaction site in the Cav1.2 N-terminus downstream of the previously identified W52 locus that is formed by residue C106, and which functionally partakes in global CDI. We also show that the Brugada syndrome mutation A39V disrupts global CDI, but not the surface expression of neuronal Cav1.2 channels as previously described. Over the course of our research we also discovered that mutant CaM molecules alter activation properties of Cav1.2 channels in the absence of calcium and surprisingly, in a manner which can be augmented by the channel N-terminus. Finally we show that a CaMKII binding site in the N-terminus of Cav1.2 is formed by four residues (CISI) and is critical for channel expression and function. Ablation of CISI produces channels which express poorly at the surface of cells, but which also have dramatically increased channel function, which offsets the trafficking defect. Thus our data indicate that surface expression and functional regulation of Cav1.2 channels by CaM and CaMKII is more complex than previously thought, and explicitly involves the channel N-terminal domain.