Department of Biochemical Science and Technology, and Institute of Microbiology and Biochemistry, National Taiwan University, Taipei, Taiwan.
PLoS One. 2012;7(4):e35336. doi: 10.1371/journal.pone.0035336. Epub 2012 Apr 10.
Post-translational regulation plays an important role in cellular metabolism. Earlier studies showed that the activity of plastidial starch phosphorylase (Pho1) may be regulated by proteolytic modification. During the purification of Pho1 from sweet potato roots, we observed an unknown high molecular weight complex (HX) showing Pho1 activity. The two-dimensional gel electrophoresis, mass spectrometry, and reverse immunoprecipitation analyses showed that HX is composed of Pho1 and the 20S proteasome. Incubating sweet potato roots at 45°C triggers a stepwise degradation of Pho1; however, the degradation process can be partially inhibited by specific proteasome inhibitor MG132. The proteolytically modified Pho1 displays a lower binding affinity toward glucose 1-phosphate and a reduced starch-synthesizing activity. This study suggests that the 20S proteasome interacts with Pho1 and is involved in the regulation of the catalytic activity of Pho1 in sweet potato roots under heat stress conditions.
翻译后调控在细胞代谢中起着重要作用。早期研究表明，质体淀粉磷酸化酶（Pho1）的活性可能受蛋白水解修饰调控。在从甘薯根中纯化Pho1的过程中，我们观察到一种具有Pho1活性的未知高分子量复合物（HX）。二维凝胶电泳、质谱和反向免疫沉淀分析表明，HX由Pho1和20S蛋白酶体组成。将甘薯根在45°C下孵育会引发Pho1的逐步降解；然而，该降解过程可被特异性蛋白酶体抑制剂MG132部分抑制。经蛋白水解修饰的Pho1对1-磷酸葡萄糖的结合亲和力较低，淀粉合成活性降低。本研究表明，在热胁迫条件下，20S蛋白酶体与Pho1相互作用并参与调控甘薯根中Pho1的催化活性。
