Molecular Basis for Membrane Lipid Homeostasis

摘要 围绕不同细胞器的膜双层的脂质组成是独特的， 结构脂质和信号脂质，如磷酸肌醇，使每个隔室具有不同的生化 以及其功能所固有的生物物理特性。在这个MIRA提案中，我们解决了基本问题， 细胞如何维持这些不同的脂质组成，即使在连续的光， 囊泡运输和室间脂质交换。我们的研究将集中在两个鲜为人知的 控制脂质稳态的机制：膜接触部位的脂质交换和脂质重塑 多功能磷酸肌醇激酶/磷酸酶复合物。膜接触部位，其中两个 细胞器进入紧密并列，正在出现在膜脂质动力学中发挥关键作用， 体内平衡为了发现在这些位点发生的过程及其分子基础，我们正在探索 哪些蛋白质定位在那里，它们的功能是什么，它们是如何以及何时在那里被招募的，以及它们的活性如何。 是受管制的。在下一个项目期间，我们的研究将集中在VPS 13和相关蛋白质上，这是我们的建议。 初步数据，包括一个新的家庭的脂质转运蛋白。这些研究预示着令人兴奋的新见解 进入膜生物学，包括长期存在的问题，线粒体和自噬体如何 隔离膜，既不连接到完善的囊泡运输途径，可能会获得他们的 膜脂膜接触部位也可以调节磷脂酰肌醇脂质种类的水平 在不同的隔室，但调节脂质激酶和脂质磷酸酶外周相关 单个细胞器的膜双层可能在控制局部 磷酸肌醇水平。为了更好地了解磷酸肌醇稳态的机制，我们 表征这些酶，其通过磷酸化可逆地相互转化磷酸肌醇种类， 和肌醇头基的去磷酸化。特别是，在下一个项目期间，我们将重点关注如何 磷脂酰肌醇-（3，5）-二磷酸（PI（3，5）P2）的水平，其在心脏的生物学中起着核心作用。 溶酶体/空泡由PIKfyve复合物调节。PI（3，5）P2代谢的机制 一直难以捉摸，部分原因是这个大会的复杂性，其中包括至少三个不同的 蛋白质和拮抗性脂质激酶和脂质磷酸酶活性。在体外研究这种复合物， 从活细胞中正在进行的许多过程中，将是至关重要的理解PI（3，5）P2的合成和 降解是单独调节并最终协调的。对于这些项目，我们将利用 在体外的结构，生物化学和生物物理技术的专业知识，然后测试出现的假设功能 通过良好的合作或与细胞生物学家同事协商。

Abstract The lipid composition of the membrane bilayer surrounding different cellular organelles is unique both in terms of structural lipids and signaling lipids like the phosphoinositides, lending each compartment distinct biochemical and biophysical characteristics intrinsic to its function. In this MIRA proposal, we address the fundamental and largely unexplored question of how cells maintain these distinct lipid compositions, even in light of continuous vesicle trafficking and lipid exchange between compartments. Our research will focus on two poorly understood mechanisms for controlling lipid homeostasis: lipid exchange at membrane contact sites and lipid remodeling by multi-functional phosphoinositide kinase/phosphatase complexes. Membrane contact sites, where two organelles come into close apposition, are emerging to play a critical role in membrane lipid dynamics and homeostasis. To discover the processes occurring at such sites and their molecular basis, we are exploring which proteins localize there, what their function is, how and when are they recruited there, and how their activity is regulated. Our studies in the next project period will focus on VPS13 and related proteins, suggested by our preliminary data to comprise a new family of lipid transport proteins. These studies promise exciting new insights into membrane biology, including for the long-standing questions of how mitochondria and the autophagosomal isolation membrane, neither connected to well-established vesicular trafficking pathways, may acquire their membrane lipids. Membrane contact sites can also modulate the levels of phosphoinositide lipid species present at different compartments, but regulation by lipid kinases and lipid phosphatases peripherally associated with the membrane bilayer of individual organelles likely plays a more significant role in controlling local phosphoinositide levels. To better understand the mechanisms governing phosphoinositide homeostasis, we are characterizing these enzymes, which reversibly interconvert phosphoinositide species via the phosphorylation and dephosphorylation of their inositol headgroups. In particular, in the next project period, we will focus on how levels of phosphatidylinositol-(3,5)-bisphosphate (PI(3,5)P2), which plays a central role in the biology of the lysosome/vacuole, are regulated by the PIKfyve complex. The mechanisms underlying PI(3,5)P2 metabolism have been elusive, owing in part to the complexity of this assembly which comprises at least three different proteins and antagonistic lipid kinase and lipid phosphatase activities. Studying this complex in vitro, separate from the many processes ongoing in living cells, will be critical in understanding how PI(3,5)P2 synthesis and degradation are individually regulated and ultimately coordinated. For these projects, we will leverage our expertise in structural, biochemical, and biophysical techniques in vitro, then test arising hypotheses functionally via well-established collaborations or in consultation with cell biologist colleagues.