异钙调素结合在质膜胞外位点上并导致胞内钙离子水平...
异钙调素结合在质膜胞外位点上并导致胞内钙离子水平上升
钙调蛋白（CaM）是一种高保守性的细胞内钙离子感应器。在植物中，胞外CaM也作为一个多肽信号影响许多生理功能，但是其在细胞质外的结合位点至今仍存在争议。
2009年5月，中科院植物所林金星研究组在《JBC》上发表文章，研究人员利用CaM交联QD系统对植物细胞表面CaM结合位点进行单分子水平检测，发现QD-CaM能选择性的结合在质膜外空间，并且通过高分辨率透射电子显微镜进行了进一步定位，证实了胞外CaM结合位点确实存在于植物细胞膜表面，但在植物细胞壁上却没有CaM结合位点。此研究为钠米技术在植物细胞研究上的应用提供了有力的证据。此外，研究人员还利用显微注射、FRET以及非损伤微测（SIET）等技术证明了胞外CaM在与其胞外结合为点结合后，可以引起胞内第二信使Ca2+信号的增强，这些发现说明了植物胞外CaM可以通过介导跨膜信号而发挥其信号肽的功能。
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http://xuyue.net/xylt/attachment.php?aid=165&noupdate=yes¬humb=yes
http://www.ebiotrade.com/newsf/2009-3/2009325172825.htm
关键词：钙调素（Calmodulin, CaM）；离子选择性电极（Ion-selective microelectrodes）；质膜（Plasma membrane）
参考文献：Wang et al. J. Biol. Chem..2009, 284: 12000-12007
全文下载：http://dmdb.ibcas.ac.cn/ljx文章/JBC--wang%20qingli.pdf
Abstract
Calmodulin (CaM) is a highly conserved intracellular calcium sensor. In plants, CaM also appears to be present in the apoplasm, and application of exogenousCaMhas 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 CaMcan 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.
