The cotranslational maturation of the type I membrane glycoprotein tyrosinase: the heat shock protein 70 system hands off to the lectin-based chaperone system.
The cotranslational maturation of the type I membrane glycoprotein tyrosinase: the heat shock protein 70 system hands off to the lectin-based chaperone system.
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DOI：
10.1091/mbc.e05-05-0381
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发表时间：
2005-08
影响因子：
3.3
通讯作者：
Ning Wang;Robert Daniels;D. Hebert
中科院分区：
文献类型：
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作者：
Ning Wang;Robert Daniels;D. Hebert
真核分泌性货物的成熟起始于多肽链进入内质网腔时的互补和共移位。在这里，我们的特点是人类I型膜糖蛋白酪氨酸酶的共翻译成熟途径。概括的共翻译事件，包括糖基化，信号序列切割，伴侣结合，和氧化，简短的成绩单缺乏终止密码子在体外翻译的存在下，半透性黑素细胞膜。这创造了一系列长度增加的核糖体/translocon-被捕链，模拟共翻译折叠过程中的中间体。最初，发现新生链与热休克蛋白（Hsp）70家族成员BiP相关。随着新生链的延长和额外的聚糖的转移，BiP结合迅速下降，并在其位置上招募基于凝集素的伴侣系统。凝集素伴侣钙连接蛋白结合到新生链后，添加两个聚糖，钙网蛋白协会后，添加第三个。当钙连接蛋白和钙网蛋白结合时，聚糖特异性氧化还原酶ERp 57与酪氨酸酶交联。这个时间与酪氨酸酶内二硫键的形成及其信号序列的切割相吻合。因此，酪氨酸酶成熟与Hsp 70系统协同启动，并传递给凝集素伴侣系统，该系统首先使用钙连接蛋白，然后使用钙网蛋白。有趣的是，野生型和突变型白化病酪氨酸酶的成熟途径的分歧已经可以观察到translocon逮捕新生链。
The maturation of eukaryotic secretory cargo initiates cotranslationally and cotranslocationally as the polypeptide chain emerges into the endoplasmic reticulum lumen. Here, we characterized the cotranslational maturation pathway for the human type I membrane glycoprotein tyrosinase. To recapitulate the cotranslational events, including glycosylation, signal sequence cleavage, chaperone binding, and oxidation, abbreviated transcripts lacking a stop codon were in vitro translated in the presence of semipermeabilized melanocyte membranes. This created a series of ribosome/translocon-arrested chains of increasing lengths, simulating intermediates in the cotranslational folding process. Initially, nascent chains were found to associate with the heat shock protein (Hsp) 70 family member BiP. As the nascent chains elongated and additional glycans were transferred, BiP binding rapidly decreased and the lectin-based chaperone system was recruited in its place. The lectin chaperone calnexin bound to the nascent chain after the addition of two glycans, and calreticulin association followed upon the addition of a third. The glycan-specific oxidoreductase ERp57 was cross-linked to tyrosinase when calnexin and calreticulin were associated. This timing coincided with the formation of disulfide bonds within tyrosinase and the cleavage of its signal sequence. Therefore, tyrosinase maturation initiates cotranslationally with the Hsp70 system and is handed off to the lectin chaperone system that first uses calnexin before calreticulin. Interestingly, divergence in the maturation pathways of wild-type and mutant albino tyrosinase can already be observed for translocon-arrested nascent chains.