異鈣調素結合在質膜胞外位點上并導致胞內鈣離子水平...

發布時間：2020-07-20 21:04 原文鏈接：異鈣調素結合在質膜胞外位點上并導致胞內鈣離子水平...

異鈣調素結合在質膜胞外位點上并導致胞內鈣離子水平上升

鈣調蛋白（CaM）是一種高保守性的細胞內鈣離子感應器。在植物中，胞外CaM也作為一個多肽信號影響許多生理功能，但是其在細胞質外的結合位點至今仍存在爭議。

2009年5月，中科院植物所林金星研究組在《JBC》上發表文章，研究人員利用CaM交聯QD系統對植物細胞表面CaM結合位點進行單分子水平檢測，發現QD-CaM能選擇性的結合在質膜外空間，并且通過高分辨率透射電子顯微鏡進行了進一步定位，證實了胞外CaM結合位點確實存在于植物細胞膜表面，但在植物細胞壁上卻沒有CaM結合位點。此研究為鈉米技術在植物細胞研究上的應用提供了有力的證據。此外，研究人員還利用顯微注射、FRET以及非損傷微測（SIET）等技術證明了胞外CaM在與其胞外結合為點結合后，可以引起胞內第二信使Ca²⁺信號的增強，這些發現說明了植物胞外CaM可以通過介導跨膜信號而發揮其信號肽的功能。

關鍵詞：鈣調素（Calmodulin, CaM）；離子選擇性電極（Ion-selective microelectrodes）；質膜（Plasma membrane）

參考文獻：Wang et al. J. Biol. Chem..2009, 284: 12000-12007

全文下載：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.

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