GENES CONTROLLING LDL RECEPTOR STRUCTURE AND FUNCTION

该研究的长期目标是确定低密度脂蛋白（LDL）受体介导的内吞作用的分子细节，这可以帮助提供脂蛋白代谢和动脉粥样硬化的基本理解。 此外，这项工作可能有助于新的见解的高尔基体的结构和功能的一般机制，它发挥了核心作用，在控制许多完整的膜和内腔可溶性蛋白质的流动，通过真核细胞，也参与这些蛋白质的翻译后修饰（糖基化，硫酸化）以及糖脂的合成。 通过从隐性LDL受体（LDLR）缺陷的中国仓鼠卵巢（CHO）细胞突变体ldlB和ldlC中表达克隆鉴定的两种细胞质蛋白ldlBp和ldlCp在控制腔内高尔基体加工反应（例如，糖缀合物合成和重塑）。 ldlB和ldlC无效突变体在多个腔高尔基体反应中表现出多效性缺陷，这导致LDLR和许多其他糖缀合物的异常合成。 ldlBp和ldlCp都与高尔基体的细胞质表面结合，并且是非常大的大分子复合物（约950 kD，“ldlCp复合物”）的组分。 初步研究表明，ldlCp对C.优雅 本研究的目的是阐明高尔基体细胞质表面ldlBp/ldlCp系统控制高尔基体细胞腔酶活性的机制。 我们将1）确定系统的其他组件（另外的复合物组分、高尔基体受体、腔内因子和条件），2）描述ldlBp/ldlCp-复合物系统对正常和突变细胞中高尔基体的结构、组成和功能的影响，和3）表征ldlBp/ldlCp-高尔基体系统的组分的物理和功能相互作用，使用多种技术[免疫化学、蛋白质纯化、配体印迹、生物物理学（EM、离心）、克隆、碳水化合物分析、体外细胞器测定、体细胞遗传学等]。 这是可能的，该系统的分子表征将提供基本的新见解的合成和加工的LDLR和其他膜和分泌蛋白，以及高尔基体的结构和功能在高等真核生物。 这应该进一步加深我们对复杂的生理和病理生理（例如，家族性高胆固醇血症、动脉粥样硬化）过程，其基于LDLR的功能和功能障碍。

The long term goal of the proposed study is to define the molecular details of low density lipoprotein (LDL) receptor- mediated endocytosis, which can help provide fundamental understanding of lipoprotein metabolism and atherosclerosis. In addition, this work may contribute new insights into the general mechanisms underlying the structure and function of the Golgi apparatus, which plays a central role in controlling the flow of many integral membrane and lumenal soluble proteins through eukaryotic cells and also participates in the posttranslational modifications of these proteins (glycosylation, sulfation) as well as in glycolipid synthesis. Two cytoplasmic proteins, ldlBp and ldlCp, which were identified by expression cloning from recessive LDL receptor (LDLR)-defective Chinese hamster ovary (CHO) cell mutants, ldlB and ldlC, play critical roles in controlling intralumenal Golgi processing reactions (e.g., glycoconjugate synthesis and remodeling) in mammals. The ldlB and ldlC null mutants exhibit pleiotropic defects in multiple lumenal Golgi reactions, which result in the abnormal synthesis the LDLR and many other glycoconjugates. Both ldlBp and ldlCp bind to the cytoplasmic surface of the Golgi and are components of a very large macromolecular complex (approximately 950 kD, 'ldlCp complex'). Preliminary studies indicate that ldlCp is essential for development in the worm C. elegans. The goal of this proposal is to elucidate the mechanism underlying the control of Golgi lumenal enzymatic activities by the ldlBp/ldlCp system from the cytoplasmic surface of the Golgi. We will 1) identify additional components of the system (additional complex components, Golgi receptor, intralumenal factors and conditions), 2) describe the effects of the ldlBp/ldlCp-complex system on the structure, composition, and function of the Golgi in normal and mutant cells, and 3) characterize the physical and functional interactions of the components of the ldlBp/ldlCp-Golgi system, using a variety of techniques [immunochemistry, protein purification, ligand blotting, biophysics (EM,centrifugation), cloning, carbohydrate analysis, in vitro organelle assays, somatic cell genetics, and others]. It is likely that the molecular characterization of this system will provide fundamental new insights into the synthesis and processing of the LDLR and other membrane and secreted proteins, as well as the structure and function of the Golgi in higher eukaryotes. This should further our understanding of the complex physiologic and pathophysiologic (e.g., familial hypercholesterolemia, atherosclerosis) processes which are based on the function and dysfunction of the LDLR.