Radhakrishnan Arun, Sun Li-Ping, Kwon Hyock Joo, Brown Michael S, Goldstein Joseph L
Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas 75390, USA.
Mol Cell. 2004 Jul 23;15(2):259-68. doi: 10.1016/j.molcel.2004.06.019.
Mammalian cells control their membrane composition by regulating the vesicular transport of membrane-bound sterol regulatory element binding proteins (SREBPs) from endoplasmic reticulum (ER) to Golgi. Transport is blocked by cholesterol, which triggers SCAP, the SREBP escort protein, to bind to Insigs, which are ER retention proteins. The cholesterol trigger mechanism is unknown. Using recombinant SCAP purified in detergent, we show that cholesterol acts by binding with high affinity and specificity to the 767 amino acid octahelical membrane region of SCAP. This octahelical region contains a conserved pentahelical sterol-sensing domain found in six other polytopic membrane proteins. We show that the membrane domain of SCAP is a tetramer and that cholesterol binding is inhibited by cationic amphiphiles, raising the possibility of allosteric regulation by positively charged phospholipids. The current studies show that cells control their cholesterol content through receptor-ligand interactions and not through changes in the physical properties of the membrane.
哺乳动物细胞通过调节膜结合的固醇调节元件结合蛋白（SREBPs）从内质网（ER）到高尔基体的囊泡运输来控制其膜组成。胆固醇会阻断这种运输，它会触发SREBP护送蛋白SCAP与内质网保留蛋白Insigs结合。胆固醇触发机制尚不清楚。我们使用在去污剂中纯化的重组SCAP表明，胆固醇通过与SCAP的767个氨基酸的八螺旋膜区域高亲和力且特异性地结合而起作用。这个八螺旋区域包含一个在其他六种多跨膜蛋白中发现的保守的五螺旋固醇感应结构域。我们表明SCAP的膜结构域是四聚体，并且阳离子两亲物会抑制胆固醇结合，这增加了带正电荷的磷脂进行变构调节的可能性。目前的研究表明，细胞通过受体 - 配体相互作用而非通过膜物理性质的变化来控制其胆固醇含量。
