Harmon Alice C
Department of Botany, University of Florida, Gainesville, FL, USA.
Gravit Space Biol Bull. 2003 Jun;16(2):83-90.
The importance of calcium ions in coupling physiological responses to external and developmental signals in plants has been well documented. Recently, Plieth and Trewavas (Plant Physiology, 2002, 129: 786-796) have shown that gravistimulation, too, elicits changes in the concentration of cytoplasmic Ca2+ in Arabidopsis plants. Cytoplasmic calcium brings about responses by interacting with target proteins, many of which contain EF-hand calcium-binding motifs. In plants there are at least five classes of protein kinases, all of which are in the CDPK/SnRK family, that either contain EF-hands within their structure or interact with proteins that contain EF-hands. Calcium-dependent protein kinases (CDPKs) and calcium and calmodulin-activated protein kinases (CCaMKs) both contain EF hands in their C-terminal domains and are activated by the binding of calcium. SnRK3s (Group 3 of the SNF-1 related kinases) bind to proteins that contain three EF hands, and some are activated by calcium. Members of two other protein kinase classes, plant calmodulin-dependent protein kinase (CaMK) and CDPK-related kinase (CRK), bind to calmodulin, but it remains to be seen whether the activity of these enzymes is regulated by calcium/calmodulin. This paper will review what is known about the structure and the regulation of these protein kinases and address the question of why there is such a plethora of calcium-regulated kinases in plants.
钙离子在植物中将生理反应与外部和发育信号偶联过程中的重要性已有充分记载。最近，普利思和特里瓦瓦斯（《植物生理学》，2002年，第129卷：786 - 796页）表明，重力刺激也会引发拟南芥植物细胞质Ca2+浓度的变化。细胞质钙通过与靶蛋白相互作用引发反应，其中许多靶蛋白含有EF手型钙结合基序。在植物中至少有五类蛋白激酶，它们都属于CDPK/SnRK家族，要么在其结构中含有EF手型结构，要么与含有EF手型结构的蛋白相互作用。钙依赖性蛋白激酶（CDPKs）和钙及钙调蛋白激活的蛋白激酶（CCaMKs）在其C末端结构域都含有EF手型结构，并通过钙的结合而被激活。SnRK3s（SNF-1相关激酶的第3组）与含有三个EF手型结构的蛋白结合，有些还被钙激活。另外两类蛋白激酶，即植物钙调蛋白依赖性蛋白激酶（CaMK）和CDPK相关激酶（CRK），与钙调蛋白结合，但这些酶的活性是否受钙/钙调蛋白调节还有待观察。本文将综述关于这些蛋白激酶的结构和调节的已知信息，并探讨植物中为何存在如此众多受钙调节的激酶这一问题。
