The Role of Phospholipid Turnover in Membrane Protein Function

描述（由申请人提供）：膜稳态是细胞功能的一个基本方面，需要协调控制多种代谢活动，包括参与脂质合成的生物合成酶和参与脂质周转的磷脂酶。脂质体内平衡的缺陷可导致许多疾病的发展，包括肥胖症、糖尿病和癌症。在这里提出的初步结果中，我们已经确定YPK1，酵母同系物的人血清和糖皮质激素诱导的激酶（SGK1），作为一种新的调节磷脂酰胆碱（PC）营业额在质膜（PM）。重要的是，人SGK1挽救了与ypk1突变体相关的生长缺陷，表明人和酵母蛋白之间的功能保守性。ypk1酵母突变体表现出增加的Plb 1介导的PC脱酰在PM。此外，在ypk1突变体中发生的加速的Plb 1活性是细胞存活的补偿机制，因为与ypk1突变体相比，ypk1plb 1双突变体表现出增加的生长缺陷和增加的对细胞壁扰动剂calcofluor的敏感性。由于PC是一种丰富的磷脂，其代谢的改变可能会影响膜的组成和物理性质，因此，膜蛋白存在于其中。事实上，我们已经确定了两个PM蛋白的活动受到损害的损失YPK1或PLB1。我们的中心假设是，删除YPK1或PLB1改变PM脂质组成，这反过来又影响了整体PM蛋白的活性，并导致生长缺陷。在这里提出的研究中，我们将描绘的过程中，Ypk 1和Plb 1调节积分PM蛋白的活性，包括检查的作用，Plb 1和Ypk 1在控制PM脂质组成。此外，将使用单层脂质囊泡检查其活性响应于Ypk 1或Plb 1的损失而降低的PM通透酶的脂质需求。

DESCRIPTION (provided by applicant): Membrane homeostasis is a fundamental aspect of cell function and requires the coordinated control of multiple metabolic activities, including biosynthetic enzymes involved in lipid synthesis and phospholipases involved in lipid turnover. Defects in lipid homeostasis can contribute to the development of many diseases, including obesity, diabetes, and cancer. In preliminary results presented here, we have identified Ypk1, the yeast homolog of the human serum and glucocorticoid-induced kinase (SGK1), as a novel regulator of phosphatidylcholine (PC) turnover at the plasma membrane (PM). Importantly, human SGK1 rescues growth defects associated with a ypk1 mutant, indicating functional conservation between the human and yeast proteins. A ypk1 yeast mutant exhibits increased Plb1-mediated PC deacylation at the PM. Furthermore, the accelerated Plb1 activity that occurs in a ypk1 mutant is a compensatory mechanism for cell survival, as a ypk1plb1 double mutant exhibits an increased growth defect and increased sensitivity to the cell wall perturbing agent, calcofluor, as compared to the ypk1 mutant. Because PC is an abundant phospholipid, alterations in its metabolism might be expected to affect the composition and physical properties of the membrane, and, therefore, membrane proteins that reside within. Indeed, we have identified two PM proteins whose activities are compromised by loss of Ypk1 or Plb1. Our central hypothesis is that deletion of YPK1 or PLB1 alters PM lipid composition, which, in turn, impinges upon the activity of integral PM proteins and results in growth defects. In the studies proposed here, we will delineate the process by which Ypk1 and Plb1 modulate integral PM protein activity, including examining the role that Plb1 and Ypk1 play in controlling PM lipid composition. In addition, the lipid requirements of a PM permease whose activity is reduced in response to loss of Ypk1 or Plb1 will be examined using unilamellar lipid vesicles.