Beard Nicole A, Wei Lan, Cheung Stephanie N, Kimura Takashi, Varsányi Magdolna, Dulhunty Angela F
John Curtin School of Medical Research, Australian National University, PO Box 334, Canberra, Australian Capital Territory 2601, Australia.
Cell Calcium. 2008 Oct;44(4):363-73. doi: 10.1016/j.ceca.2008.01.005.
Calcium signaling, intrinsic to skeletal and cardiac muscle function, is critically dependent on the amount of calcium stored within the sarcoplasmic reticulum. Calsequestrin, the main calcium buffer in the sarcoplasmic reticulum, provides a pool of calcium for release through the ryanodine receptor and acts as a luminal calcium sensor for the channel via its interactions with triadin and junctin. We examined the influence of phosphorylation of calsequestrin on its ability to store calcium, to polymerise and to regulate ryanodine receptors by binding to triadin and junctin. Our hypothesis was that these parameters might be altered by phosphorylation of threonine 353, which is located near the calcium and triadin/junctin binding sites. Although phosphorylation increased the calcium binding capacity of calsequestrin nearly 2-fold, it did not alter calsequestrin polymerisation, its binding to triadin or junctin or inhibition of ryanodine receptor activity at 1 mM luminal calcium. Phosphorylation was required for calsequestrin binding to junctin when calcium concentration was low (100 nM), and ryanodine receptors were activated by dephosphorylated calsequestrin when it bound to triadin alone. These novel data shows that phosphorylated calsequestrin is required for high capacity calcium buffering and suggest that ryanodine receptor inhibition by calsequestrin is mediated by junctin.
钙信号传导是骨骼肌和心肌功能所固有的，严重依赖于肌浆网内储存的钙量。肌集钙蛋白是肌浆网中的主要钙缓冲蛋白，它提供了一个钙池，通过兰尼碱受体释放钙，并通过与三联蛋白和连接蛋白的相互作用作为该通道的管腔钙传感器。我们研究了肌集钙蛋白磷酸化对其储存钙、聚合以及通过与三联蛋白和连接蛋白结合来调节兰尼碱受体能力的影响。我们的假设是，位于钙及三联蛋白/连接蛋白结合位点附近的苏氨酸353的磷酸化可能会改变这些参数。尽管磷酸化使肌集钙蛋白的钙结合能力增加了近2倍，但它并未改变肌集钙蛋白的聚合、其与三联蛋白或连接蛋白的结合，也未改变在1 mM管腔钙浓度下对兰尼碱受体活性的抑制。当钙浓度较低（100 nM）时，磷酸化是肌集钙蛋白与连接蛋白结合所必需的，而当去磷酸化的肌集钙蛋白单独与三联蛋白结合时，它会激活兰尼碱受体。这些新数据表明，磷酸化的肌集钙蛋白是高容量钙缓冲所必需的，并表明肌集钙蛋白对兰尼碱受体的抑制是由连接蛋白介导的。
