Journal
JOURNAL OF CELL SCIENCE
Volume 119, Issue 10, Pages 2145-2155Publisher
COMPANY BIOLOGISTS LTD
DOI: 10.1242/jcs.02935
Keywords
voltage-dependent Ca2+ channel; JP-45; sarcoplasmic reticulum; excitation-contraction coupling
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Funding
- NIA NIH HHS [AG18755, AG13934, R29 AG013934, AG15820, R01 AG018755, R01 AG015820, R01 AG013934] Funding Source: Medline
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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 Ca(v)1. We have identified the domains of JP-45 and the Ca(v)1.1 involved in this interaction, and investigated the functional effect of JP-45. The cytoplasmic domain of JP-45, comprising residues 180, 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. beta 1a, 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 V-Q1/2 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.
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