Yang C, Gu Z W, Yang M, Gotto A M
Department of Medicine, Baylor College of Medicine, Houston, Texas.
Chem Phys Lipids. 1994 Jan;67-68:99-104. doi: 10.1016/0009-3084(94)90128-7.
Apolipoprotein B-100 (apoB-100) is the major protein in low-density lipoprotein (LDL) and contains the ligand for binding LDL to its cell surface receptor. Lipoprotein [a] (Lp[a]) is a lipoprotein that consists of LDL and apolipoprotein [a] (apo[a]). The primary structure of apoB-100 has been determined by a combination of recombinant DNA and protein sequencing methods. Using high-performance liquid chromatographic techniques, we have identified sulfhydryl and disulfide groups of apoB-100 from LDL. Sixteen of the 25 cysteine residues in apoB-100 exist in disulfide form. All 14 cysteine residues within the N terminal end of apoB-100 are linked in disulfide bridges. Using the fluorescent sulfhydryl probe, 5-iodoacetoamidofluoresceine, two free sulfhydryls of apoB-100 on LDL were identified at positions 3734 and 4190. Based on its differential susceptibility to trypsin, apoB-100 can be divided into five domains: domain 1 (residues 1-1000), largely trypsin-releasable (TR); domain 2 (residues 1001-1700), alternating TR and trypsin non-releasable (TN); domain 3 (residues 1701-3070), largely TN; domain 4 (residues 3071-4100), mainly TR and mixed; and domain 5 (residues 4101-4536), almost exclusively TN. Based on our data, we propose that the structure of apoB-100 in LDL is probably an elongated form that wraps around the LDL particle, and that Cys3734 of apoB-100 may be the cysteine residue linked to a cysteine of apo[a].
载脂蛋白B - 100（apoB - 100）是低密度脂蛋白（LDL）中的主要蛋白质，包含使LDL与其细胞表面受体结合的配体。脂蛋白[a]（Lp[a]）是一种由LDL和载脂蛋白[a]（apo[a]）组成的脂蛋白。apoB - 100的一级结构已通过重组DNA和蛋白质测序方法相结合得以确定。利用高效液相色谱技术，我们已鉴定出LDL中apoB - 100的巯基和二硫键基团。apoB - 100的25个半胱氨酸残基中有16个以二硫键形式存在。apoB - 100 N末端的所有14个半胱氨酸残基都通过二硫键相连。使用荧光巯基探针5 - 碘乙酰氨基荧光素，在LDL上的apoB - 100的3734位和4190位鉴定出两个游离巯基。基于其对胰蛋白酶的不同敏感性，apoB - 100可分为五个结构域：结构域1（第1 - 1000位残基），大部分可被胰蛋白酶释放（TR）；结构域2（第1001 - 1700位残基），TR和不可被胰蛋白酶释放（TN）交替出现；结构域3（第1701 - 3070位残基），大部分为TN；结构域4（第3071 - 4100位残基），主要是TR且混合存在；结构域5（第4101 - 4536位残基），几乎全为TN。基于我们的数据，我们提出LDL中apoB - 100的结构可能是一种围绕LDL颗粒的细长形式，并且apoB - 100的Cys3734可能是与apo[a]的一个半胱氨酸相连的半胱氨酸残基。
