APOB

This gene product is the main apolipoprotein of chylomicrons and low density lipoproteins (LDL), and is the ligand for the LDL receptor. It occurs in plasma as two main isoforms, apoB-48 and apoB-100: the former is synthesized exclusively in the gut and the latter in the liver. The intestinal and the hepatic forms of apoB are encoded by a single gene from a single, very long mRNA. The two isoforms share a common N-terminal sequence. The shorter apoB-48 protein is produced after RNA editing of the apoB-100 transcript at residue 2180 (CAA->UAA), resulting in the creation of a stop codon, and early translation termination. Mutations in this gene or its regulatory region cause hypobetalipoproteinemia, normotriglyceridemic hypobetalipoproteinemia, and hypercholesterolemia due to ligand-defective apoB, diseases affecting plasma cholesterol and apoB levels. [provided by RefSeq, Dec 2019]

本基因产物为胆固醇酯转运蛋白（Chylomicrons）及低密度脂蛋白（Low Density Lipoproteins，LDL）的主要载脂蛋白，并作为LDL受体的配体。其在血浆中存在两种主要异构体，即apoB-48和apoB-100：前者专一性地在肠道合成，而后者则在肝脏中生成。apoB的肠肝型由单一基因编码，该基因转录自一条极长的mRNA。两种异构体共享一个共同的N端序列。较短的apoB-48蛋白是在apoB-100转录本的第2180位核苷酸（CAA变为UAA）经过RNA编辑后产生的，从而形成了一个终止密码子，导致早期翻译终止。该基因或其调控区域的突变可导致低β脂蛋白血症、正常甘油三酯血症性低β脂蛋白血症以及由于配体缺陷性apoB引起的血脂异常，这些疾病均影响血浆胆固醇和apoB水平。[提供者：RefSeq，2019年12月]