Calmodulin Binds to Extracellular Sites on the Plasma Membrane of Plant Cells and Elicits a Rise in Intracellular Calcium Concentration*
Calmodulin Binds to Extracellular Sites on the Plasma Membrane of Plant Cells and Elicits a Rise in Intracellular Calcium Concentration*
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DOI：
10.1074/jbc.m808028200
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发表时间：
2009-05
影响因子：
4.8
通讯作者：
Qinli Wang;Bo Chen;P. Liu;Maozhong Zheng;Yuqing Wang;Sujuan Cui;Daye Sun;Xiaohong Fang;Chun-Ming Liu;W. J. Lucas;Jinxing Lin
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文献类型：
--
作者：
Qinli Wang;Bo Chen;P. Liu;Maozhong Zheng;Yuqing Wang;Sujuan Cui;Daye Sun;Xiaohong Fang;Chun-Ming Liu;W. J. Lucas;Jinxing Lin
钙调素（CaM）是一种高度保守的细胞内钙感受器。在植物中，CaM似乎也存在于质外体中，外源CaM的应用已被证明可以影响许多生理功能作为多肽信号;然而，其相应的质外体结合位点的存在和定位仍然存在争议。为了鉴定作用位点，采用CaM缀合的量子点（QD）系统在植物细胞表面进行单分子水平检测。使用这种方法，我们表明，QD-CaM选择性地结合到质膜的外表面上的网站，这是进一步证实了高分辨率透射电子显微镜。用离子选择性微电极测量质膜上的Ca 2+通量，结果表明外源性CaM诱导净流入原生质体。与这些通量研究一致，钙绿葡聚糖和FRET实验证实，应用CaM/QD-CaM引起细胞质Ca 2+水平的增加。这些结果支持的假设，质外钙调素可以作为一个信号剂。这些研究结果进行了讨论，钙调素作为一个质外肽配体介导的跨膜信号在植物界。
Calmodulin (CaM) is a highly conserved intracellular calcium sensor. In plants, CaM also appears to be present in the apoplasm, and application of exogenous CaM has been shown to influence a number of physiological functions as a polypeptide signal; however, the existence and localization of its corresponding apoplasmic binding sites remain controversial. To identify the site(s) of action, a CaM-conjugated quantum dot (QD) system was employed for single molecule level detection at the surface of plant cells. Using this approach, we show that QD-CaM binds selectively to sites on the outer surface of the plasma membrane, which was further confirmed by high resolution transmission electron microscopy. Measurements of Ca2+ fluxes across the plasma membrane, using ion-selective microelectrodes, demonstrated that exogenous CaM induces a net influx into protoplasts. Consistent with these flux studies, calcium-green-dextran and FRET experiments confirmed that applied CaM/QD-CaM elicited an increase in cytoplasmic Ca2+ levels. These results support the hypothesis that apoplasmic CaM can act as a signaling agent. These findings are discussed in terms of CaM acting as an apoplasmic peptide ligand to mediate transmembrane signaling in the plant kingdom.