Schwartz Kevin J, Bangs James D
Department of Medical Microbiology & Immunology, University of Wisconsin Medical School, Madison, Wisconsin 53711, USA.
J Eukaryot Microbiol. 2007 Jan-Feb;54(1):22-4. doi: 10.1111/j.1550-7408.2006.00231.x.
The structure, biosynthesis, and attachment of glycosylphosphatidylinositol (GPI) anchors were all first determined for the variant surface glycoprotein (VSG) of African trypanosomes, and all of the basic aspects of this work have been shown to be universal in eukaryotic organisms. However, the role of GPI anchors in protein trafficking within trypanosomes has lagged behind the more standard eukaryotic model systems such as yeast and polarized epithelial cells. Trypanosomes are also highly polarized cells in which all endocytosis and exocytosis intersect at a discrete domain of the plasma membrane, the flagellar pocket. Within these convergent pathways trafficking of GPI anchored proteins correlates strongly with valence: homodimeric VSG with two GPIs is stably incorporated into the cell surface coat, heterodimeric transferrin receptor with a single GPI is found in the flagellar pocket and is slowly delivered to the lysosome for degradation, and recombinant GPI minus VSG reporters are rapidly degraded in the lysosome. Here we summarize recent data confirming this correlation using a tool kit of recombinant GPI anchored reporters, including a reporter designed to be conditionally modulated between a GPI valence of one and two.
糖基磷脂酰肌醇（GPI）锚定物的结构、生物合成及附着，最初都是针对非洲锥虫的可变表面糖蛋白（VSG）确定的，并且这项工作的所有基本方面已被证明在真核生物中具有普遍性。然而，GPI锚定物在锥虫体内蛋白质运输中的作用，落后于酵母和极化上皮细胞等更为标准的真核模型系统。锥虫也是高度极化的细胞，其中所有的内吞作用和外排作用都在质膜的一个离散区域——鞭毛袋处交汇。在这些汇聚途径中，GPI锚定蛋白的运输与价态密切相关：带有两个GPI的同二聚体VSG稳定地整合到细胞表面被膜中，带有单个GPI的异二聚体转铁蛋白受体存在于鞭毛袋中，并缓慢地被输送到溶酶体进行降解，而重组的无GPI的VSG报告蛋白在溶酶体中迅速降解。在此，我们总结了最近使用重组GPI锚定报告蛋白工具包证实这种相关性的数据，包括一种设计用于在一价和二价GPI之间进行条件调节的报告蛋白。
