Association of Triadin to the Junctional Sarcoplasmic Reticulum of Skeletal Muscle Cells

Abstract

The junctional sarcoplasmic reticulum (jSR) of skeletal muscle cells contains several proteins that participate to the mechanisms of Ca2+ release in the process of excitation-contraction coupling. Among these proteins, ryanodine receptor, triadin, junctin and calsequestrin have been found to associate into a stable complex. We recently reported that assembly of jSR domains is accompanied by a strong decrease in the mobility fraction of jSR proteins (Cusimano et al., PNAS 2009). In particular, we found that the mobility of triadin appeared to be mediated by its intraluminal region (aa 232-729). In order to identify the minimal regions required for association of triadin to the jSR, deletion mutants of the luminal domain (triadin Δ232-440 and triadin Δ441-729) were generated and expressed in primary muscle myotubes. Analysis of the mobility fraction of these mutants showed that they do not differ from wild type triadin, indicating that either one of the two regions is sufficient to provide a strong association of the protein to the jSR. Interestingly, we found that the luminal region of triadin contains several defined domains, including a coiled coil region and short amino acids repeats, that are present in the region between aa 232-440 and aa 441-729, where they may mediate protein-protein interactions. Results on the role of these amino acid repeats in mediating triadin association with the jSR will be reported.