Rybalchenko Volodymyr, Hwang Sung-Yong, Rybalchenko Nataliya, Koulen Peter
Department of Pharmacology and Neuroscience, University of North Texas Health Science Center at Fort Worth, 3500 Camp Bowie Blvd., Fort Worth, TX 76107, USA.
Int J Biochem Cell Biol. 2008;40(1):84-97. doi: 10.1016/j.biocel.2007.06.023. Epub 2007 Jul 13.
Ryanodine receptors (RyRs) amplify intracellular Ca(2+) signals by massively releasing Ca(2+) from intracellular stores. Exaggerated chronic Ca(2+) release can trigger cellular apoptosis underlying a variety of neurodegenerative diseases. Aberrant functioning of presenilin-1 (PS1) protein instigates Ca(2+)-dependent apoptosis, providing a basis for the "calcium hypothesis" of Alzheimer's disease (AD). To get insight into this problem, we hypothesized that the previously reported physical interaction between RyR and PS1 modulates functional properties of the RyR. We generated a soluble cytoplasmic N-terminal fragment of PS1 comprising the first 82 amino acid (PS1 NTF(1-82)), the candidate for interaction with putative cytoplasmic modulatory sites of the RyR, and studied its effect on single channel currents of mouse brain RyRs incorporated in lipid bilayers. PS1 NTF(1-82) strongly increased both mean currents (EC(50)=12nM, Hill coefficient (n(H)) approximately 1) and open probability for higher sublevels for single RyR channels (EC(50)=7nM, n(H) approximately 2). Bell-shaped Ca(2+)-activation curve remained unchanged, suggesting that PS1 NTF(1-82) allosterically potentiates RyRs, but that the channel still requires Ca(2+) for activation. Corroborating such an independent mechanism, the RyR potentiation by PS1 NTF(1-82) was overridden by receptor desensitization at high [Ca(2+)] (pCa>5). This potentiation of RyR by PS1 NTF(1-82) reveals a new mechanism of physiologically relevant PS1-regulated Ca(2+) release from intracellular stores, which could be alternative or additional to recently reported intracellular Ca(2+) leak channels formed by PS1 holoproteins.
兰尼碱受体（RyRs）通过从细胞内钙库大量释放钙离子来放大细胞内钙离子信号。过度的慢性钙离子释放可引发多种神经退行性疾病所潜在的细胞凋亡。早老素-1（PS1）蛋白的异常功能会引发钙离子依赖性凋亡，为阿尔茨海默病（AD）的“钙假说”提供了依据。为深入了解这一问题，我们推测先前报道的RyR与PS1之间的物理相互作用会调节RyR的功能特性。我们生成了一个包含前82个氨基酸的PS1可溶性细胞质N端片段（PS1 NTF(1-82)），它是与RyR假定的细胞质调节位点相互作用的候选物，并研究了其对整合到脂质双分子层中的小鼠脑RyRs单通道电流的影响。PS1 NTF(1-82)显著增加了单RyR通道的平均电流（半数有效浓度（EC(50)）=12nM，希尔系数（n(H)）约为1）以及更高亚水平的开放概率（EC(50)=7nM，n(H)约为2）。钟形的钙离子激活曲线保持不变，这表明PS1 NTF(1-82)通过变构增强了RyRs，但通道仍需要钙离子来激活。为证实这种独立机制，在高钙离子浓度（pCa>5）下受体脱敏会抑制PS1 NTF(1-82)对RyR的增强作用。PS1 NTF(1-82)对RyR的这种增强作用揭示了一种生理相关的PS1调节细胞内钙库钙离子释放的新机制，这可能是对最近报道的由PS1全蛋白形成的细胞内钙离子泄漏通道的一种替代或补充。
