Lackey Kimberly Helms, Pope Patricia Marie, Johnson Margaret Dean
Department of Biological Sciences, The University of Alabama, Tuscaloosa, Alabama 35487, USA.
Plant Physiol. 2003 Aug;132(4):2240-7. doi: 10.1104/pp.103.020610.
We have studied the expression of 1L-myoinositol-1-phosphate synthase (MIPS; EC 5.5.1.4) in developing organs of Phaseolus vulgaris to define genetic controls that spatially regulate inositol phosphate biosynthesis. MIPS, the pivotal biosynthetic enzyme in inositol metabolism, is the only enzyme known to catalyze the conversion of glucose 6-phosphate to inositol phosphate. It is found in unicellular and multicellular eukaryotes and has been isolated as a soluble enzyme from both. Thus, it is widely accepted that inositol phosphate biosynthesis is largely restricted to the cytosol. Here, we report findings that suggest the enzyme is also expressed in membrane-bound organelles. Microscopic and biochemical analyses detected MIPS expression in plasma membranes, plastids, mitochondria, endoplasmic reticula, nuclei, and cell walls of bean. To address mechanisms by which the enzyme could be targeted to or through membranes, MIPS genes were analyzed for sorting signals within primary structures and upstream open reading frames that we discovered through our sequence analyses. Comprehensive computer analyses revealed putative transit peptides that are predicted to target the enzyme to different cellular compartments. Reverse transcriptase PCR experiments suggest that these putative targeting peptides are expressed in bean roots and leaves.
我们研究了菜豆发育器官中1L-肌醇-1-磷酸合酶（MIPS；EC 5.5.1.4）的表达，以确定在空间上调节肌醇磷酸生物合成的遗传控制机制。MIPS是肌醇代谢中的关键生物合成酶，是已知唯一催化6-磷酸葡萄糖转化为肌醇磷酸的酶。它存在于单细胞和多细胞真核生物中，并且已从两者中分离为可溶性酶。因此，人们普遍认为肌醇磷酸生物合成主要局限于细胞质溶胶。在此，我们报告的研究结果表明该酶也在膜结合细胞器中表达。显微镜和生化分析检测到菜豆的质膜、质体、线粒体、内质网、细胞核和细胞壁中存在MIPS表达。为了研究该酶靶向膜或穿过膜的机制，我们对MIPS基因进行了分析，以寻找通过序列分析发现的一级结构和上游开放阅读框中的分选信号。全面的计算机分析揭示了预测将该酶靶向不同细胞区室的假定转运肽。逆转录酶PCR实验表明这些假定的靶向肽在菜豆根和叶中表达。
