Otsu Mieko, Bertoli Gloria, Fagioli Claudio, Guerini-Rocco Elena, Nerini-Molteni Silvia, Ruffato Elena, Sitia Roberto
DiBiT San Raffaele Scientific Institute, and Università Vita-Salute San Raffaele, Milano, Italy.
Antioxid Redox Signal. 2006 Mar-Apr;8(3-4):274-82. doi: 10.1089/ars.2006.8.274.
Disulfide bonds are formed in the endoplasmic reticulum (ER) by sequential interchange reactions: Ero1alpha and Ero1beta transfer oxidative equivalents to protein disulfide isomerase (PDI), which in turn oxidizes cargo proteins. Neither Ero1alpha nor Ero1beta contains known ER localization motif(s), raising the question of how they are retained in this organelle. Here the authors show that, unlike endogenous molecules, overexpressed Ero1alpha and Ero1beta are secreted by HeLa transfectants, suggesting saturation of their normal retention mechanism(s). Co-expression of either PDI or ERp44 prevents Ero1 secretion in a KDEL/RDEL dependent way. Covalent interactions between ERp44 and Ero1 are essential for retention. In contrast, a mutant PDI lacking the four cysteines in the two active sites still inhibits secretion, albeit less efficiently. PDI and ERp44 compete for Ero1 binding. PDI also prevents Ero1 aggregation and dimerization, thus chaperoning its own oxidase. This dynamic retention mechanism of Ero1 may be important for fine-tuning the regulation of ER redox homeostasis and quality control.
二硫键在内质网（ER）中通过顺序交换反应形成：Ero1α和Ero1β将氧化当量转移给蛋白质二硫键异构酶（PDI），而PDI反过来氧化货物蛋白。Ero1α和Ero1β均不包含已知的内质网定位基序，这就提出了它们如何保留在该细胞器中的问题。本文作者表明，与内源性分子不同，过表达的Ero1α和Ero1β由HeLa转染细胞分泌，这表明其正常保留机制已饱和。共表达PDI或ERp44以KDEL/RDEL依赖的方式阻止Ero1分泌。ERp44与Ero1之间的共价相互作用对于保留至关重要。相比之下，在两个活性位点缺少四个半胱氨酸的突变型PDI仍然抑制分泌，尽管效率较低。PDI和ERp44竞争与Ero1结合。PDI还可防止Ero1聚集和二聚化，从而陪伴其自身的氧化酶。Ero1的这种动态保留机制对于微调内质网氧化还原稳态和质量控制的调节可能很重要。
