Free oligosaccharides in the cytosol of Caenorhabditis elegans are generated through endoplasmic reticulum-Golgi trafficking
Free oligosaccharides in the cytosol of Caenorhabditis elegans are generated through endoplasmic reticulum-Golgi trafficking
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DOI：
10.1074/jbc.m700805200
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发表时间：
2007-07-27
影响因子：
4.8
通讯作者：
Yamamoto, Kenji
中科院分区：
文献类型：
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作者：
Kato, Toshihiko;Kitamura, Kumiko;Yamamoto, Kenji
真核细胞胞浆中的游离寡糖(FOSS)主要是在错误折叠的糖蛋白的内质网相关降解(ERAD)过程中产生的。我们分析了线虫秀丽线虫的FOS，以阐明其详细的降解途径。主要的FOSS是高甘露糖型，含有3-9个人残基。约94%的FOSS在其还原端有一个GlcNAc(FOS-GN1)，其余6%的FOSS有两个GlcNAc(FOS-GN2)。胞内β-N-乙酰氨基葡萄糖苷酶突变体(Tm1208)积累了FOS-GN2，表明该酶参与了FOS-GN2向FOS-GN1的转化。野生型中最丰富的FOS是Man(5)GlcNAc(1)，它是M5A的异构体(Man Alpha 1-3(Man Alpha 1-6)Man Alpha 1-6(Man Alpha 1-3)Man beta 1-4GlcNAc)，与哺乳动物中相应的M5B‘(Man Alpha 1-2man Alpha 1-2 man Alpha 1-3(Man Alpha 1-6)Man beta 1-4GlcNAc)不同。用高尔基α-甘露糖苷酶I抑制剂处理的蠕虫的FOS分析显示，Man(5)GlcNAc(1)减少，Man(7)GlcNAc(1)增加。这些结果表明，高尔基体α-甘露糖苷酶I类酶参与了Man(5-6)-GlcNAc(1)的产生，这与哺乳动物不同，它涉及胞浆α-甘露糖苷酶。因此，我们假设线虫中的大部分自由/开源软件是通过高尔基体贩运产生的。对高尔基体α-甘露糖苷酶II突变体(Tm1078)的FOSS分析支持这一观点，因为在突变体中发现了由高尔基体驻留的GlcNAc-转移酶I形成的GlcNAc(1)Man(5)GlcNAc(1)作为FOS。我们得出的结论是，线虫体内大量错误折叠的糖蛋白被贩运到高尔基体，并直接或间接被逆转到细胞质中进行降解。
Free oligosaccharides (FOSs) in the cytosol of eukaryotic cells are mainly generated during endoplasmic reticulum (ER)-associated degradation (ERAD) of misfolded glycoproteins. We analyzed FOS of the nematode Caenorhabditis elegans to elucidate its detailed degradation pathway. The major FOSs were high mannose-type ones bearing 3-9 Man residues. About 94% of the total FOSs had one GlcNAc at their reducing end (FOS-GN1), and the remaining 6% had two GlcNAc (FOS-GN2). A cytosolic endo-beta-N-acetylglucosaminidase mutant (tm1208) accumulated FOS-GN2, indicating involvement of the enzyme in conversion of FOS-GN2 into FOS-GN1. The most abundant FOS in the wild type was Man(5)GlcNAc(1), the M5A' isomer (Man alpha 1- 3(Man alpha 1-6)Man alpha 1-6(Man alpha 1-3)Man beta 1-4GlcNAc), which is different from the corresponding M5B' (Man alpha 1-2Man alpha 1- 2Man alpha 1-3(Man alpha 1-6)Man beta 1-4GlcNAc) in mammals. Analyses of FOS in worms treated with Golgi alpha-mannosidase I inhibitors revealed decreases in Man(5)GlcNAc(1) and increases in Man(7)GlcNAc(1). These results suggested that Golgi alpha-mannosidase I-like enzyme is involved in the production of Man(5-6)- GlcNAc(1), which is unlike in mammals, in which cytosolic alpha-mannosidase is involved. Thus, we assumed that major FOSs in C. elegans were generated through Golgi trafficking. Analysis of FOSs from a Golgi alpha-mannosidase II mutant (tm1078) supported this idea, because GlcNAc(1)Man(5)GlcNAc(1), which is formed by the Golgi-resident GlcNAc-transferase I, was found as a FOS in the mutant. We concluded that significant amounts of misfolded glycoproteins in C. elegans are trafficked to the Golgi and are directly or indirectly retro-translocated into the cytosol to be degraded.