The triad targeting signal of the skeletal muscle calcium channel is localized in the COOH terminus of the alpha(1S) subunit

The specific localization of L-type Ca(2+) channels in skeletal muscle triads is critical for their normal function in excitation-contraction (EC) coupling. Reconstitution of dysgenic myotubes with the skeletal muscle Ca(2+) channel alpha(1S) subunit restores Ca(2+) currents, EC coupling, and the no...

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Bibliographic Details
Published in:The Journal of cell biology 2000-10, Vol.151 (2), p.467-478
Main Authors: Flucher, B E, Kasielke, N, Grabner, M
Format: Article
Language:English
Subjects:
Action Potentials
Amino Acid Sequence
Calcium - metabolism
Calcium Channels, L-Type - metabolism
Electric Conductivity
Intercellular Junctions - metabolism
Molecular Sequence Data
Muscle, Skeletal - physiology
Patch-Clamp Techniques
Protein Isoforms
Protein Sorting Signals
Protein Subunits
Protein Transport
Recombinant Fusion Proteins
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Summary:The specific localization of L-type Ca(2+) channels in skeletal muscle triads is critical for their normal function in excitation-contraction (EC) coupling. Reconstitution of dysgenic myotubes with the skeletal muscle Ca(2+) channel alpha(1S) subunit restores Ca(2+) currents, EC coupling, and the normal localization of alpha(1S) in the triads. In contrast, expression of the neuronal alpha(1A) subunit gives rise to robust Ca(2+) currents but not to triad localization. To identify regions in the primary structure of alpha(1S) involved in the targeting of the Ca(2+) channel into the triads, chimeras of alpha(1S) and alpha(1A) were constructed, expressed in dysgenic myotubes, and their subcellular distribution was analyzed with double immunofluorescence labeling of the alpha(1S)/alpha(1A) chimeras and the ryanodine receptor. Whereas chimeras containing the COOH terminus of alpha(1A) were not incorporated into triads, chimeras containing the COOH terminus of alpha(1S) were correctly targeted. Mapping of the COOH terminus revealed a triad-targeting signal contained in the 55 amino-acid sequence (1607-1661) proximal to the putative clipping site of alpha(1S). Transferring this triad targeting signal to alpha(1A) was sufficient for targeting and clustering the neuronal isoform into skeletal muscle triads and caused a marked restoration of Ca(2+)-dependent EC coupling.
ISSN:0021-9525
DOI:10.1083/jcb.151.2.467