title: Mechanism of auxiliary β-subunit-mediated membrane targeting of L-type (Ca(V)1.2) channels.
abstract: Ca(2+) influx via Ca(V)1/Ca(V)2 channels drives processes ranging from neurotransmission to muscle contraction. Association of a pore-forming α(1) and cytosolic β is necessary for trafficking Ca(V)1/Ca(V)2 channels to the cell surface through poorly understood mechanisms. A prevalent idea suggests β binds the α(1) intracellular I-II loop, masking an endoplasmic reticulum (ER) retention signal as the dominant mechanism for Ca(V)1/Ca(V)2 channel membrane trafficking. There are hints that other α(1) subunit cytoplasmic domains may play a significant role, but the nature of their potential contribution is unclear. We assessed the roles of all intracellular domains of Ca(V)1.2-α(1C) by generating chimeras featuring substitutions of all possible permutations of intracellular loops/termini of α(1C) into the β-independent Ca(V)3.1-α(1G) channel. Surprisingly, functional analyses demonstrated α(1C) I-II loop strongly increases channel surface density while other cytoplasmic domains had a competing opposing effect. Alanine-scanning mutagenesis identified an acidic-residue putative ER export motif responsible for the I-II loop-mediated increase in channel surface density. β-dependent increase in current arose as an emergent property requiring four α(1C) intracellular domains, with the I-II loop and C-terminus being essential. The results suggest β binding to the α(1C) I-II loop causes a C-terminus-dependent rearrangement of intracellular domains, shifting a balance of power between export signals on the I-II loop and retention signals elsewhere.
authors: Department of Physiology and Cellular Biophysics, Columbia University, College of Physicians and Surgeons, New York, NY 10032, USA.
authors: Kun
authors: K
authors: Fang
authors: Henry M
authors: HM
authors: Colecraft
mesh_terms: D000595:Amino Acid Sequence; D020746:Calcium Channels, L-Type / Q000502:physiology*; D020747:Calcium Channels, T-Type / Q000502:physiology; D051243:Caveolin 2 / Q000502:physiology; D002462:Cell Membrane / Q000502:physiology*; D002678:Chimera; D057809:HEK293 Cells; D006801:Humans; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D021122:Protein Subunits / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: C121855:CACNA1G protein, human; C495544:CAV2 protein, human; D020746:Calcium Channels, L-Type; D020747:Calcium Channels, T-Type; D051243:Caveolin 2; C419385:L-type calcium channel alpha(1C); D021122:Protein Subunits