Voncken Frank, van Hellemond Jaap J, Pfisterer Iris, Maier Alexander, Hillmer Stephan, Clayton Christine
Zentrum für Molekulare Biologie Heidelberg, Im Neuenheimer Feld 282, D-69120 Heidelberg, Germany.
J Biol Chem. 2003 Sep 12;278(37):35299-310. doi: 10.1074/jbc.M301811200. Epub 2003 Jun 26.
Microbody division in mammalian cells, trypanosomes, and yeast depends on the PEX11 microbody membrane proteins. The function of PEX11 is not understood, and the suggestion that it affects microbody (peroxisome) numbers in mammals and yeast, because it plays a role in beta-oxidation of fatty acids, is controversial. PEX11 and two PEX11-related proteins, GIM5A and GIM5B, are the predominant membrane proteins of the microbodies (glycosomes) of Trypanosoma brucei. The compartmentation of glycosomal enzymes is essential in trypanosomes. Deletion of the GIM5A gene from the form of the parasite that lives in the mammalian blood has no effect on trypanosome growth, but depletion of GIM5B on a gim5a null background causes death. We show here that procyclic trypanosomes, adapted for life in the Tsetse fly vector, survive without GIM5A and with very low levels of GIM5B. The depleted cells have fewer glycosomes than usual and are osmotically fragile, which is a novel observation for a microbody defect. Thus trypanosomes require both GIM5B and PEX11 for the maintenance of normal glycosome numbers. Procyclic cells lacking GIM5A, like mouse cells partially defective in PEX11, have fewer ether-linked phospholipids, even when GIM5B levels are not reduced. Metabolite measurements on GIM5A/B-depleted bloodstream form trypanosomes suggested a change in the flux through the glycolytic pathway. We conclude that PEX11 family proteins play important roles in determining microbody membrane structure, with secondary effects on a subset of microbody metabolic pathways.
哺乳动物细胞、锥虫和酵母中的微体分裂依赖于PEX11微体膜蛋白。PEX11的功能尚不清楚，有人认为它影响哺乳动物和酵母中的微体（过氧化物酶体）数量，因为它在脂肪酸的β氧化中起作用，但这一观点存在争议。PEX11以及两种与PEX11相关的蛋白GIM5A和GIM5B是布氏锥虫微体（糖体）的主要膜蛋白。糖体酶的区室化在锥虫中至关重要。从生活在哺乳动物血液中的寄生虫形式中删除GIM5A基因对锥虫生长没有影响，但在gim5a基因缺失的背景下耗尽GIM5B会导致死亡。我们在此表明，适应采采蝇载体生活的前循环锥虫在没有GIM5A且GIM5B水平极低的情况下仍能存活。耗尽GIM5B的细胞比正常细胞的糖体更少，并且对渗透压敏感，这是微体缺陷的一个新发现。因此，锥虫维持正常糖体数量既需要GIM5B也需要PEX11。缺乏GIM5A的前循环细胞，就像PEX11部分缺陷的小鼠细胞一样，即使GIM5B水平没有降低，醚键连接的磷脂也更少。对耗尽GIM5A/B的血流形式锥虫的代谢物测量表明糖酵解途径的通量发生了变化。我们得出结论，PEX11家族蛋白在决定微体膜结构中起重要作用，并对微体代谢途径的一个子集产生次要影响。
