title: The junctional SR protein JP-45 affects the functional expression of the voltage-dependent Ca2+ channel Cav1.1.
abstract: JP-45, an integral protein of the junctional face membrane of the skeletal muscle sarcoplasmic reticulum (SR), colocalizes with its Ca2+ -release channel (the ryanodine receptor), and interacts with calsequestrin and the skeletal-muscle dihydropyridine receptor Cav1. We have identified the domains of JP-45 and the Cav1.1 involved in this interaction, and investigated the functional effect of JP-45. The cytoplasmic domain of JP-45, comprising residues 1-80, interacts with Cav1.1. JP-45 interacts with two distinct and functionally relevant domains of Cav1.1, the I-II loop and the C-terminal region. Interaction between JP-45 and the I-II loop occurs through the alpha-interacting domain in the I-II loop. beta1a, a Cav1 subunit, also interacts with the cytosolic domain of JP-45, and its presence drastically reduces the interaction between JP-45 and the I-II loop. The functional effect of JP-45 on Cav1.1 activity was assessed by investigating charge movement in differentiated C2C12 myotubes after overexpression or depletion of JP-45. Overexpression of JP-45 decreased peak charge-movement and shifted VQ1/2 to a more negative potential (-10 mV). JP-45 depletion decreased both the content of Cav1.1 and peak charge-movements. Our data demonstrate that JP-45 is an important protein for functional expression of voltage-dependent Ca2+ channels.
authors.affiliation: Department of Anaesthesia, Basel University Hospital, Hebelstrasse 20, 4031 Basel, Switzerland.
authors.forename: Ayuk A
authors.initials: AA
authors.lastname: Anderson
authors.forename: Xavier
authors.initials: X
authors.lastname: Altafaj
authors.forename: Zhenlin
authors.initials: Z
authors.lastname: Zheng
authors.forename: Zhong-Min
authors.initials: ZM
authors.lastname: Wang
authors.forename: Osvaldo
authors.initials: O
authors.lastname: Delbono
authors.forename: Michel
authors.initials: M
authors.lastname: Ronjat
authors.forename: Susan
authors.initials: S
authors.lastname: Treves
authors.forename: Francesco
authors.initials: F
authors.lastname: Zorzato
mesh_terms: D000818:Animals; D020746:Calcium Channels, L-Type / Q000096:biosynthesis* / Q000378:metabolism; D002155:Calsequestrin / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D020868:Gene Silencing; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018482:Muscle, Skeletal / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
chemical_list: D020746:Calcium Channels, L-Type; D002155:Calsequestrin; C418633:JSRP1 protein, human; D008565:Membrane Proteins; D012333:RNA, Messenger