STRUCTURE/FUNCTION ANALYSIS OF ACAT

该实验室的长期研究兴趣是了解 调节胆固醇代谢的细胞和分子 水平 酰基辅酶A：胆固醇酰基转移酶（ACAT）被认为是 在膳食胆固醇吸收、肝脏 脂蛋白的组装和分泌，以及产生泡沫细胞， 动脉粥样硬化斑块 申请人的实验室最近 提出ACAT可能是一种变构酶， 胆固醇传感器; ACAT与ER胆固醇的结合可能 引起配体诱导的ACAT结构/构型变化 蛋白质，将酶从非活性形式转化为活性形式。 form. 配体诱导的构型变化可以通过 ACAT全酶中多个亚基之间的相互作用。 的 申请人的实验室最近已经成功地纯化了 重组人ACAT蛋白在CHO细胞中表达至均一。 我们还合成了一种新的光不稳定胆固醇类似物。 与 这些分子试剂可用，在目前的提案中，我们建议 利用重组DNA技术和生物化学方法， ACAT的结构功能分析，以检验ACAT的有效性。 变构调节模型，并阐明的分子基础， 胆固醇和ACAT之间的传感机制。 我们的具体目标是：1.确定ER中ACAT的拓扑结构 膜的 2.为了研究均匀ACAT的性质， 重构的PC囊泡。 3.为了确定胆固醇结合 通过光亲和标记和位点特异性 诱变 4.为了产生由以下组成的ACAT异源寡聚复合物， 活性ACAT单体和非活性ACAT单体，并检查 它们在体外的特性。 5.为了检查的寡聚体结构 体外和完整CHO细胞中的ACAT。

The long-term research interest of this laboratory is to understand regulation of cholesterol metabolism at the cellular and molecular level. Acyl-coenzyme A: cholesterol acyltransferase (ACAT) is believed to play important roles in dietary cholesterol absorption, in hepatic lipoprotein assembly and secretion, and in producing foam cells in atherosclerotic plaques. The applicant's laboratory has recently proposed that ACAT may be an allosteric enzyme and serves as a cholesterol sensor in the ER; binding of ER cholesterol by ACAT may cause a ligand induced structural/configuration change in the ACAT protein, which converts the enzyme from an inactive form to an active form. The ligand-induced configurational change may occur through interactions among multiple subunits in the ACAT holoenzyme. The applicant's laboratory very recently has succeeded in purifying the recombinant human ACAT protein expressed in CHO cells to homogeneity. We have also synthesized a new photolabile cholesterol analog. With these molecular reagents available, in the current proposal, we propose to use the recombinant DNA technology and biochemical methods to conduct structure-function analysis of ACAT, to test the validity of the allosteric regulation model, and to elucidate the molecular basis of the sensing mechanism between cholesterol and ACAT. Our specific aims are: 1. To determine the topology of ACAT in the ER membrane. 2. To study properties of the homogeneous ACAT in reconstituted PC vesicles. 3. To identify the cholesterol binding site(s) within ACAT by photoaffinity labelling and by site-specific mutagenesis. 4. To produce ACAT hetero-oligomeric complex composed of the active ACAT monomer and the inactive ACAT monomer, and to examine their properties in vitro. 5. To examine the oligomeric structure of ACAT in vitro and in intact CHO cells.