Atzel A, Wetterau J R
Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, Ohio 45267-0575.
Biochemistry. 1994 Dec 27;33(51):15382-8. doi: 10.1021/bi00255a019.
The gene for the microsomal triglyceride transfer protein (MTP) is defective in subjects with the genetic disease abetalipoproteinemia, indicating that MTP is essential for the assembly of apolipoprotein B containing lipoproteins. In vitro, MTP is a lipid molecule binding protein that catalyzes lipid transport between membranes by a shuttle mechanism. In this study, the lipid binding properties of MTP were examined. MTP was incubated with donor phosphatidylcholine vesicles of varying neutral lipid composition. MTP was subsequently reisolated by ultracentrifugation, and MTP-bound lipid was quantitated. When the triolein content of the vesicles was increased up to 4 mol %, neutral lipid binding to MTP increased proportionately, while phosphatidylcholine binding appeared to remain constant around two molecules per MTP. Using phosphatidylcholine emulsions containing 60 mol % triolein as the donor particles resulted in only a slight increase in triolein binding to MTP. The highest triolein:MTP ratio observed was (0.20-0.25):1. Differences in the neutral and phospholipid binding properties of MTP were observed by measuring the transport of lipid from MTP to acceptor vesicles. Transport of triolein was rapid and complete, while phosphatidylcholine transport was biphasic, containing rapid and slow phases. These results indicated that MTP contains more than one class of lipid molecule binding site. Measurements of fluorescent lipid transport from donor vesicles to MTP supported this hypothesis. The transport of pyrene-labeled triglyceride from donor particles to MTP was rapid, while phosphatidylcholine transfer had fast and slow phases. From these data, we propose that MTP contains at least two distinct classes of lipid molecule binding sites that differ in function. The fast site or sites are responsible for lipid transport.
微粒体甘油三酯转运蛋白（MTP）基因在患有遗传性疾病无β脂蛋白血症的个体中存在缺陷，这表明MTP对于含载脂蛋白B的脂蛋白组装至关重要。在体外，MTP是一种脂质分子结合蛋白，通过穿梭机制催化膜间脂质转运。在本研究中，对MTP的脂质结合特性进行了检测。将MTP与不同中性脂质组成的供体磷脂酰胆碱囊泡一起孵育。随后通过超速离心重新分离MTP，并对与MTP结合的脂质进行定量。当囊泡中三油精含量增加至4摩尔％时，与MTP结合的中性脂质成比例增加，而磷脂酰胆碱结合似乎在每个MTP约两个分子左右保持恒定。使用含有60摩尔％三油精的磷脂酰胆碱乳液作为供体颗粒，导致三油精与MTP的结合仅略有增加。观察到的最高三油精：MTP比例为（0.20 - 0.25）：1。通过测量脂质从MTP到受体囊泡的转运，观察到MTP在中性和磷脂结合特性方面的差异。三油精的转运迅速且完全，而磷脂酰胆碱的转运是双相的，包括快速和缓慢阶段。这些结果表明MTP含有不止一类脂质分子结合位点。从供体囊泡到MTP的荧光脂质转运测量结果支持了这一假设。芘标记的甘油三酯从供体颗粒到MTP的转运迅速，而磷脂酰胆碱的转移有快相和慢相。根据这些数据，我们提出MTP至少含有两类功能不同的独特脂质分子结合位点。快速位点负责脂质转运。
