Lee S H, Kim M C, Heo W D, Kim J C, Chung W S, Park C Y, Park H C, Cheong Y H, Kim C Y, Lee K J, Bahk J D, Lee S Y, Cho M J
Department of Biochemistry, Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Chinju 660-701, South Korea.
Biochim Biophys Acta. 1999 Aug 17;1433(1-2):56-67. doi: 10.1016/s0167-4838(99)00149-1.
In plants, multiple calmodulin (CaM) isoforms exist in an organism which vary in their primary structures in as much as 32 residues out of their 148 amino acids. These CaM isoforms show differences in their expression patterns and/or target enzyme activation ability. To further understand the biological significance of CaM isoforms, we examined whether CaM isoforms act on specific regulatory targets. In gel overlay assays on various soybean tissue extracts, surprisingly, two soybean CaM isoforms (SCaM-1 and SCaM-4) did not show significant differences in their target binding protein profiles, although they exhibited minor differences in their relative target binding affinities. In addition, both SCaM isoforms not only effectively bound five known plant CaMBPs, but also showed competitive binding to these proteins. Finally, immunolocalization experiments with the SCaM proteins in sections of various tissues using specific antibodies revealed similar distribution patterns for the SCaM isoforms except for root tissues, which indicates that the SCaM isoforms are concomitantly expressed in most plant tissues. These results suggest that CaM isoforms may compete for binding to CaMBPs in vivo. This competitive nature of CaM isoforms may allow modulation of Ca(2+)/CaM signaling pathways by virtue of relative abundance and differential target activation potency.
在植物中，一个生物体中存在多种钙调蛋白（CaM）亚型，它们在其148个氨基酸中有多达32个残基的一级结构有所不同。这些CaM亚型在其表达模式和/或靶酶激活能力上存在差异。为了进一步了解CaM亚型的生物学意义，我们研究了CaM亚型是否作用于特定的调控靶点。在对各种大豆组织提取物进行的凝胶覆盖分析中，令人惊讶的是，两种大豆CaM亚型（SCaM-1和SCaM-4）在其靶标结合蛋白谱上没有显示出显著差异，尽管它们在相对靶标结合亲和力上表现出微小差异。此外，两种SCaM亚型不仅有效地结合了五种已知的植物CaMBP，而且还显示出对这些蛋白的竞争性结合。最后，使用特异性抗体对各种组织切片中的SCaM蛋白进行免疫定位实验，结果显示除根组织外，SCaM亚型的分布模式相似，这表明SCaM亚型在大多数植物组织中同时表达。这些结果表明，CaM亚型可能在体内竞争与CaMBP的结合。CaM亚型的这种竞争性质可能通过相对丰度和不同的靶标激活能力来调节Ca(2+)/CaM信号通路。
