Interactions between N and C termini of α_1Csubunit regulate inactivation of Ca_V1.2 L-type Ca²⁺channel

Abstract

(2016) Keywords: binding, calcium channel, calmodulin, C-terminus, Ca V 1.2, inactivation, L-type, N-terminusThe modulation and regulation of voltage-gated Ca 2C channels is affected by the pore-forming segments, the cytosolic parts of the channel, and interacting intracellular proteins. In this study we demonstrate a direct physical interaction between the N terminus (NT) and C terminus (CT) of the main subunit of the L-type Ca 2C channel Ca V 1.2, a 1C , and explore the importance of this interaction for the regulation of the channel. We used biochemistry to measure the strength of the interaction and to map the location of the interaction sites, and electrophysiology to investigate the functional impact of the interaction. We show that the full-length NT (amino acids 1-154) and the proximal (close to the plasma membrane) part of the CT, pCT (amino acids 1508-1669) interact with sub-micromolar to low-micromolar affinity. Calmodulin (CaM) is not essential for the binding. The results further suggest that the NT-CT interaction regulates the channel's inactivation, and that Ca 2C , presumably through binding to calmodulin (CaM), reduces the strength of NT-CT interaction. We propose a molecular mechanism in which NT and CT of the channel serve as levers whose movements regulate inactivation by promoting changes in the transmembrane core of the channel via S1 (NT) or S6 (pCT) segments of domains I and IV, accordingly, and not as a kind of pore blocker. We hypothesize that Ca 2C -CaM-induced changes in NT-CT interaction may, in part, underlie the acceleration of Ca V 1.2 inactivation induced by Ca 2C entry into the cell.

Protein kinase A regulates C‐terminally truncated CaV1.2 in Xenopus oocytes: roles of N‐ and C‐termini of the α1C subunit

“…; Benmocha Guggenheimer et al . ). We further propose that the new mechanism may be one of two or more complementary pathways of PKA regulation of Ca V 1.2 in the heart.…”

“…), and demonstrated a direct interaction (binding) between the NT and CT of α 1C (Benmocha Guggenheimer et al . ). We hypothesize that the ‘NT–CT scaffold’ participates in PKA regulation of Ca V 1.2 gating.…”

Exercise and Ion-Channel Remodeling in Vascular Smooth Muscle During Hypertension: Therapeutic Implications

“…1). The I domain has a cytosolic N terminus and the IV domain has a cytosolic C terminus, and the N terminus-C terminus interaction plays a critical role in the inactivation of the channel and in general ion regulation [3]. The cytoplasmic region between the II and III transmembrane domains contains variable sequences that differentiate Ca V 1.2 and Cav1.3 subtypes [60].…”

“…The Ca V 1.2 channel activation triggers the functional specificity of the intracellular signal transduction pathways via activated Ca 2+ second-messenger pathways [60]. Ca 2+ influx through Ca V 1.2 channels can directly link membrane potential changes to the stimulation of intracellular signaling cascades [3]. For instance, membrane depolarization activates Ca V 1.2 channels, which mediates Ca 2+ influx into VSMCs to initiate cell contraction.…”

“…As a buffer mechanism, Ca 2+ influx through Ca V 1.2 channels triggers Ca 2+ release (referred to as Ca 2+ sparks) from internal stores such as sarcoplasmic ryanodine receptors (RyRs), which sequentially activates local Ca 2+ -dependent activation of nearby BK Ca channels, and contributes to the negative feedback regulation of myogenic tone. Because excess Ca 2+ influx is toxic, Ca 2+ entry into the cell is precisely regulated via intrinsic and extrinsic mechanisms [3].…”