Stiles Amanda R, Qian Xun, Shears Stephen B, Grabau Elizabeth A
Department of Plant Pathology, Physiology and Weed Science, Virginia Polytechnic Institute and State University, 413 Price Hall, Blacksburg, VA 24061, USA.
FEBS Lett. 2008 Jun 11;582(13):1853-8. doi: 10.1016/j.febslet.2008.04.054. Epub 2008 May 12.
We have cloned and characterized four Itpk genes from soybean. All four recombinant Itpk proteins showed canonical Ins(1,3,4)P3 5/6-kinase activity, but a kinetic analysis raised questions about its biological significance. Instead, we provide evidence that one alternative biological role for soybean Itpks is to interconvert the Cl(-) channel inhibitor, Ins(3,4,5,6)P4, and its metabolic precursor, Ins(1,3,4,5,6)P5, within a substrate cycle. The soybean Itpks also phosphorylated Ins(3,4,6)P3 to Ins(1,3,4,6)P4 which was further phosphorylated to Ins(1,3,4,5,6)P5 by soybean Ipk2. Thus, soybean Itpks may participate in an inositol lipid-independent pathway of InsP6 synthesis.
我们从大豆中克隆并鉴定了四个肌醇多磷酸激酶（Itpk）基因。所有四种重组Itpk蛋白均表现出典型的肌醇-1,3,4-三磷酸5/6-激酶活性，但动力学分析对其生物学意义提出了疑问。相反，我们提供的证据表明，大豆Itpks的另一个生物学作用是在底物循环中使氯离子通道抑制剂肌醇-3,4,5,6-四磷酸（Ins(3,4,5,6)P4）及其代谢前体肌醇-1,3,4,5,6-五磷酸（Ins(1,3,4,5,6)P5）相互转化。大豆Itpks还将肌醇-3,4,6-三磷酸（Ins(3,4,6)P3）磷酸化为肌醇-1,3,4,6-四磷酸（Ins(1,3,4,6)P4），后者再被大豆Ipk2进一步磷酸化为肌醇-1,3,4,5,6-五磷酸（Ins(1,3,4,5,6)P5）。因此，大豆Itpks可能参与了一条不依赖于肌醇脂质的肌醇六磷酸（InsP6）合成途径。
