Secretory and membrane proteins synthesized in the endoplasmic reticulum (ER) are folded with intramolecular disulphide bonds, viz. oxidative folding, catalysed by the protein disulphide isomerase (PDI) family proteins. Here, we identified a novel soybean PDI family protein, GmPDIL6. GmPDIL6 has a single thioredoxin-domain with a putative N-terminal signal peptide and an active centre (CKHC). Recombinant GmPDIL6 forms various oligomers binding iron. Oligomers with or without iron binding and monomers exhibited a dithiol oxidase activity level comparable to those of other soybean PDI family proteins. However, they displayed no disulphide reductase and extremely low oxidative refolding activity. Interestingly, GmPDIL6 was mainly expressed in the cotyledon during synthesis of seed storage proteins and GmPDIL6 mRNA was up-regulated under ER stress. GmPDIL6 may play a role in the formation of disulphide bonds in nascent proteins for oxidative folding in the ER.

中文翻译：

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一种新型的大豆蛋白二硫键异构酶家族蛋白具有二硫醇氧化活性：GmPDIL6的鉴定和表征。

内质网（ER）中合成的分泌蛋白和膜蛋白被分子内二硫键折叠，即。氧化折叠，由蛋白质二硫键异构酶（PDI）家族蛋白催化。在这里，我们确定了一种新型的大豆PDI家族蛋白GmPDIL6。GmPDIL6具有单个硫氧还蛋白结构域和一个假定的N-末端信号肽和活性中心（CKHC）。重组GmPDIL6形成结合铁的各种寡聚物。具有或不具有铁结合的低聚物和单体表现出的二硫醇氧化酶活性水平可与其他大豆PDI家族蛋白相媲美。但是，它们没有显示出二硫化物还原酶，并且氧化折叠活性极低。有趣的是，在种子贮藏蛋白合成过程中，GmPDIL6主要在子叶中表达，并且在ER胁迫下GmPDIL6 mRNA上调。GmPDIL6可能在新生蛋白质中形成二硫键，从而在ER中发生氧化折叠。