Distinct regions of triadin are required for targeting and retention at the junctional domain of the sarcoplasmic reticulum

Ca2+ release necessary for muscle contraction occurs at the junctional domain of the sarcoplasmic reticulum (j-SR). It requires the assembly of a large multi-protein complex containing the ryanodine receptor (RyR) and additional proteins, including triadin and calsequestrin. The signals which drive these proteins to the j-SR and how they assemble to form this multi-protein complex are poorly understood. To address aspects of these questions we studied the localization, dynamic properties and molecular interactions of triadin. We identified three regions, named TR1, TR2 and TR3, that contribute to the localization of triadin at the j-SR. Fluorescence recovery after photobleaching (FRAP) experiments showed that triadin is stably associated with the j-SR and that this association is mediated by TR3. Protein pull-down experiments indicated that TR3 contains binding sites for calsequestrin-1 and that triadin clustering can be enhanced by binding to calsequestrin-1. These findings were confirmed by FRET experiments. Interestingly, the stable association of triadin to the j-SR was significantly decreased in myotubes from calsequestrin-1 knockout mice. Altogether, these results identify three regions in triadin that mediate targeting to the j-SR and reveal a role for calsequestrin-1 in promoting the stable association of triadin to the multi-protein complex associated with RyR.

Source: BJ Cell - December 11, 2013 Category: Biochemistry Authors: D Rossi, C Bencini, M Maritati, F Benini, S Lorenzini, E Pierantozzi, A Maria Scarcella, C Paolini, F Protasi, V Sorrentino Tags: BJ Cell Source Type: research