低密度脂蛋白（LDL）是人体内将胆固醇从肝脏运往外周组织/细胞的主要载体，也是动脉粥样硬化疾病的首要危险因素。作为LDL主要蛋白成分，载脂蛋白ApoB-100的结构得到广泛研究，通过免疫/冰冻电镜等方法已得到众多3D结构模型，但仍缺乏统一认识，有待其它或新方法的介入。原子力显微技术（AFM）是纳米尺度的3D结构成像技术，已用于LDL成像和尺寸测量，却因脂质成分的存在而无法探测ApoB-100的3D结构。在我们前期研究报道和预实验结果的基础上，本项目拟用温和的去污剂剔除LDL脂质成分、暴露ApoB-100分子、进行AFM原位成像和分析，再通过抗体免疫标识和酶切定位等分析其3D结构，并探究酸性环境对其3D结构的影响。本项目可为某个现有3D模型提供强有力实验证据或建立更优的新模型，对进一步阐明LDL结构和功能、了解LDL的细胞内代谢和在病理状态下（如动脉粥样硬化）的作用等具有重要的科学意义。

Low-density lipoprotein (LDL) is the major carrier delivering cholesterol derived from the liver to peripheral tissues/cells, and also is the major risk factor for atherosclerosis. As the main protein component of LDL, the structure of apolipoprotein ApoB-100 has been widely studied, and many 3-dimentional (3-D) structural models have been obtained via immuno-/cryo-electron microscopy and other techniques. Unfortunately, however, no consensus has been reached and the involvement of other research methods or new methods is needed. Atomic force microscopy (AFM) is a technique capable of detecting 3-D structures at nanoscale. Although it has been applied for imaging and size measurement of LDL, AFM could not detect the 3-D structure of ApoB-100 due to the existence of the lipid component of LDL. Based on our recently reported study and preliminary data, this project seeks to deplete the lipid component of LDL via a mild detergent, expose the protein component (i.e. ApoB-100), perform AFM imaging and analysis, and then evaluate the 3-D structure of ApoB-100 in combination with immunolabeling and enzyme cleavage, and to investigate the effects of an acidic environment on the 3-D structure of ApoB-100. This project may provide more supporting evidence for an pre-existed 3-D model of ApoB-100 or establish a novel better 3-D structural model. This project also helps to the investigation of LDL structure/functions and the understanding of the intracellular metabolism of LDL and its roles in diseases (e.g. atherosclerosis, etc.).