1. Role of Junctin Protein Interactions in Cellular Dynamics of Calsequestrin Polymer upon Calcium Perturbation.
- Author
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Keun Woo Lee, Jin-Soo Maeng, Jeong Yi Choi, Yu Ran Lee, Chae Young Hwang, Sung Sup Park, Hyun Kyu Park, Bong Hyun Chung, Seung-Goo Lee, Yeon-Soo Kim, Hyesung Jeon, Soo Hyun Eom, ChulHee Kang, Do Han Kim, and Ki-Sun Kwon
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PROTEINS , *SARCOPLASMIC reticulum , *RECOMBINANT proteins , *MUSCLE cells , *SCANNING probe microscopy - Abstract
Calsequestrin (CEQ), the major intrasarcoplasmic reticulum calcium storage protein, undergoes dynamic polymerization and depolymerization in a Ca2+-dependent manner. However, no direct evidence of CEQ depolymerization in vivo with physiological relevance has been obtained. In the present study, live cell imaging analysis facilitated characterization of the in vivo dynamics of the macromolecular CEQ structure. CSQ2 appeared as speckles in the presence of normal sarcoplasmic reticulum (SR) Ca2+ that were decondensed upon Ca2+ depletion. Moreover, CSQ2 decondensation occurred only in the stoichiometric presence of junctin (JNT). When expressed alone, CSQ2 speckles remained unchanged, even after Ca2+ depletion. FRET analysis revealed constant interactions between CSQ2 and JNT, regardless of the SR Ca2+ concentration, implying that JNT is an essential component of the CEQ scaffold. In vitro solubility assay, electron microscopy, and atomic force microscopy studies using purified recombinant proteins confirmed Ca2+ and JNT-dependent disassembly of the CSQ2 polymer. Accordingly, we conclude that reversible polymerization and depolymerization of CEQ are critical in SR Ca2+ homeostasis. [ABSTRACT FROM AUTHOR]
- Published
- 2012
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