title: Role of Junctin protein interactions in cellular dynamics of calsequestrin polymer upon calcium perturbation.
abstract: Calsequestrin (CSQ), the major intrasarcoplasmic reticulum calcium storage protein, undergoes dynamic polymerization and depolymerization in a Ca(2+)-dependent manner. However, no direct evidence of CSQ 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 CSQ structure. CSQ2 appeared as speckles in the presence of normal sarcoplasmic reticulum (SR) Ca(2+) that were decondensed upon Ca(2+) depletion. Moreover, CSQ2 decondensation occurred only in the stoichiometric presence of junctin (JNT). When expressed alone, CSQ2 speckles remained unchanged, even after Ca(2+) depletion. FRET analysis revealed constant interactions between CSQ2 and JNT, regardless of the SR Ca(2+) concentration, implying that JNT is an essential component of the CSQ scaffold. In vitro solubility assay, electron microscopy, and atomic force microscopy studies using purified recombinant proteins confirmed Ca(2+) and JNT-dependent disassembly of the CSQ2 polymer. Accordingly, we conclude that reversible polymerization and depolymerization of CSQ are critical in SR Ca(2+) homeostasis.
authors: Laboratory of Cell Signaling, Aging Research Center, Korea Research Institute of Bioscience and Biotechnology, 125 Gwahangno, Yusong, Daejeon 305-806, Korea.
authors: Keun Woo
authors: KW
authors: Lee
authors: Jin-Soo
authors: JS
authors: Maeng
authors: Jeong Yi
authors: JY
authors: Choi
authors: Yu Ran
authors: YR
authors: Lee
authors: Chae Young
authors: CY
authors: Hwang
authors: Sung Sup
authors: SS
authors: Park
authors: Hyun Kyu
authors: HK
authors: Park
authors: Bong Hyun
authors: BH
authors: Chung
authors: Seung-Goo
authors: SG
authors: Lee
authors: Yeon-Soo
authors: YS
authors: Kim
authors: Hyesung
authors: H
authors: Jeon
authors: Soo Hyun
authors: SH
authors: Eom
authors: Chulhee
authors: C
authors: Kang
authors: Do Han
authors: DH
authors: Kim
authors: Ki-Sun
authors: KS
authors: Kwon
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002155:Calsequestrin / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism*; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D055503:Protein Multimerization / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*
chemical_list: C443109:CASQ2 protein, human; D002135:Calcium-Binding Proteins; D002155:Calsequestrin; D008565:Membrane Proteins; D009124:Muscle Proteins; C514388:casq2 protein, mouse; C498841:Asph protein, mouse; D006899:Mixed Function Oxygenases; C419389:ASPH protein, human; D002118:Calcium