拟南芥鞘脂合成关键限速酶丝氨酸-棕榈酰转移酶(SPT)的AtLCB1亚基磷酸化及磷酸化对SPT功能调控的机理研究

鞘脂(sphingolipids)是真核生物的主要膜脂种类之一。鞘脂除作为膜结构成分外，还作为信号和调节分子，参与真核生物的生长、发育及逆境响应等过程的调控。丝氨酸-棕榈酰转移酶(Serine palmitoyl-transferase, 简称SPT)是鞘脂从头合成的关键限速酶,由LCB1和LCB2亚基组成，其酶活性受ORM蛋白抑制和ssSPT蛋白激活。目前有关LCB1磷酸化及磷酸化后对SPT活性调控的研究缺乏。项目组前期的研究结果发现，拟南芥中MPK3和MPK6磷酸化AtLCB1，促进多聚SPT复合体形成，复合体中AtLCB1磷酸化的比率越高酶活性越高。本项目拟研究：(1) AtLCB1的磷酸化如何调控SPT酶活性；(2) AtLCB1磷酸化后哪些种类的鞘脂合成被特异调控；(3) AtLCB1磷酸化激活SPT如何调控拟南芥生长、发育及逆境响应。研究的完成将揭示SPT活性调控的新机制及功能

Sphingolipids, a class of natural lipids comprised of a sphingoid base backbone (sphingosine), are ubiquitous in all eukaryotes and a few species in prokaryotes. Sphingolipids were previously shown to serve either as the membrane structural components of to modulate the physical properties of lipid bilayers and the activity of transmembrane proteins, or as the signal molecules to regulate various physiological processes and stress responses. Serine palmitoyltransferase (SPT) is the first committed and rate limiting enzyme in de novo sphingolipids biosynthetic pathway. The core SPT is heterodimer consisted of LCB1 and LCB2 subunits. The activity of SPT was previously shown to be inhibited by orosomucoid proteins (ORMs) and stimulated by small subunits of SPT (ssSPT). However, whether LCB1 is modified and how the modification regulates SPT activity are obscure. Our preliminary data show that, activation of MPK3 and MPK6 phosphorylate AtLCB1 in Arabidopsis. AtLCB1 phosphorylation stimulates higher oligomer SPT complex formation. The ratios of the phosphorylated AtLCB1 in SPT complex are positively correlated with SPT activity. In this project, we proposed to analyze the regulatory mechanism of SPT activity by AtLCB1 phosphorylation, identify sphingolipid species that specifically induced by AtLCB1 phosphorylation, and explore the regulation of AtLCB1 phosphorylation on plant growth, development, and stress responses. The results from this project will reveal a novel mechanism of SPT activity regulation and facilitate our understanding on the biological functions of SPT.