Different conformations of nascent polypeptides during translocation across the ER membrane.
Different conformations of nascent polypeptides during translocation across the ER membrane.
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DOI：
10.1186/1471-2121-1-3
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发表时间：
2000-01-01
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影响因子：
--
通讯作者：
von Heijne, G
中科院分区：
文献类型：
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作者：
Mingarro, I;Nilsson, I;von Heijne, G
背景：在真核细胞中，蛋白质通过连续的核糖体易位通道穿过内质网膜。目前尚不清楚蛋白质在核糖体-易位子通道内的折叠程度，之前的研究表明，核糖体内可能只可能进行有限程度的折叠（例如形成分离的α螺旋）。 结果：我们之前已经表明，通过测量跨越核糖体P位点和通道之间距离所需的残基数量，可以探测通过核糖体-易位子复合物的新生多肽链的构象。寡糖基转移酶的腔内布置的活性位点(J.Biol.Chem 271：6241-6244)。使用这种方法，我们现在表明，由水中具有强螺旋形成特性的残基（Ala，Leu）组成的模型片段在核糖体易位子通道中比由具有弱螺旋形成潜力的残基（Val，Pro）组成的模型片段具有更紧凑的构象。 结论：这里报告的工作的主要结论是（i）在核糖体易位子通道中形成延伸或更紧凑（可能是α螺旋）构象的倾向核糖体-易位子通道并不取决于模型片段是否具有停止转移功能，而是似乎反映了在水性环境中测量的氨基酸的螺旋倾向，并且（ii）停止转移序列可能采用螺旋结构并在相对于将聚糖添加到附近上游糖基化受体位点的时间的不同时间整合到内质网膜中。
BACKGROUND: In eukaryotic cells, proteins are translocated across the ER membrane through a continuous ribosome-translocon channel. It is unclear to what extent proteins can fold already within the ribosome-translocon channel, and previous studies suggest that only a limited degree of folding (such as the formation of isolated alpha-helices) may be possible within the ribosome.RESULTS: We have previously shown that the conformation of nascent polypeptide chains in transit through the ribosome-translocon complex can be probed by measuring the number of residues required to span the distance between the ribosomal P-site and the lumenally disposed active site of the oligosaccharyl transferase enzyme (J. Biol. Chem 271: 6241-6244). Using this approach, we now show that model segments composed of residues with strong helix-forming properties in water (Ala, Leu) have a more compact conformation in the ribosome-translocon channel than model segments composed of residues with weak helix-forming potential (Val, Pro).CONCLUSIONS: The main conclusions from the work reported here are (i) that the propensity to form an extended or more compact (possibly alpha-helical) conformation in the ribosome-translocon channel does not depend on whether or not the model segment has stop-transfer function, but rather seems to reflect the helical propensities of the amino acids as measured in an aqueous environment, and (ii) that stop-transfer sequences may adopt a helical structure and integrate into the ER membrane at different times relative to the time of glycan addition to nearby upstream glycosylation acceptor sites.