Study on the topology of the GPI anchor assembly

糖磷脂酰肌醇(GPI)锚被预先组装并转移到内质网中相应新生蛋白的c-末端。该组装始于内质网的管腔侧，并在内质网的胞液和管腔侧之间进行。因此，GPI锚定的前体在组装过程中必须在脂质双层之间翻转。这种触发器背后的机制还没有得到很好的表征，也没有被识别为触发器的线索。已知一些细胞系上的GPI锚定蛋白是酰化的，而大多数GPI蛋白不是酰化的。这意味着在触发器中参与的酰化是一种提示。我们已经研究了触发的时机与红白血病细胞上前体的酰化反应的关系。包括肌醇残基被酰化的前体的GPI锚点是抗性的GPI特异性pshop holipase C消化。在将预先组装的GPI转移到靶新生蛋白之后进行脱酰。因此，这一发现表明，该触发器中不涉及酰化。

The glycophosphatidylinositol (GPI) anchor is preassembled and transferred to the c-terminus of the corresponding nascent proteins in the ER. The assembly starts in the luminal side of the ER and proceeds between the cytosolic and luminal sides of the ER. Thus, precursors of GPI anchor have to flip-flop between the lipid bilayer during the assembly. The mechanisms underlying this flip-flop has not been well characterized, nor identified are cues for the flip-flop. The GPI anchor proteins on some cell lines are known to be acylated while most of the GPI proteins are not acylated. This implied that acylation involved in the flip-flop as a cue. We have investigated the timing of the flip-flop in the relation, with the acylation of the precursors on erythroleukemia cells. The GPI anchor including the precursors of which inositol residue is acylated are resistant GPI specific pshopholipase C digestion.The deacylation took after the transfer of the preassembled GPI to the target nascent proteins. This findings thus suggested that the acylation is not involved in the flip-flop.