Fu Xinmiao, Zhu Bao Ting
Department of Pharmacology, Toxicology and Therapeutics, School of Medicine, University of Kansas Medical Center, 2146 W. 39th Avenue, Kansas City, KS 66160, USA.
Arch Biochem Biophys. 2009 May 1;485(1):1-9. doi: 10.1016/j.abb.2008.12.021. Epub 2009 Jan 6.
Protein disulfide isomerase (PDI) and its homologs are catalysts of the formation of disulfide bonds in secretory proteins, and they also serve as molecular chaperones. In the present study, we investigated the redox-mediated regulation of the structures and functions of human pancreas-specific PDI homolog (PDIp). We found that formation of an inter-subunit disulfide bond in the recombinant human PDIp can alter not only its structure, but also its functions. PDIp exists predominantly as monomer under reducing conditions, but the dimeric form is significantly increased following the removal of the reducing agent, due to the formation of an inter-subunit disulfide bond. The oxidized PDIp (with an inter-subunit disulfide bond) appears to expose more hydrophobic patches and is more sensitive to protease digestion compared to the reduced form. Along with these structural changes, the oxidized PDIp also exhibits an enhanced chaperone activity. The formation of the inter-subunit disulfide bond in PDIp is mainly contributed by its non-active cysteine residue (cysteine-4), which is only present in human and primate PDIp, but not in rodent PDIp. In addition, we observed that the formation of the inter-subunit disulfide bond in PDIp is redox-dependent and is favored under oxidizing conditions, and that PDIp can function as a chaperone to form stable complexes with various non-native cellular proteins, particularly under oxidizing conditions. In light of these observations, it is concluded that the structures and functions of human PDIp are redox-regulated through formation of an inter-subunit disulfide bond between two cysteine-4 residues.
蛋白质二硫键异构酶（PDI）及其同源物是分泌蛋白中二硫键形成的催化剂，它们还充当分子伴侣。在本研究中，我们研究了氧化还原介导的人胰腺特异性PDI同源物（PDIp）的结构和功能调控。我们发现重组人PDIp中亚基间二硫键的形成不仅可以改变其结构，还可以改变其功能。在还原条件下，PDIp主要以单体形式存在，但去除还原剂后，由于亚基间二硫键的形成，二聚体形式显著增加。与还原形式相比，氧化的PDIp（具有亚基间二硫键）似乎暴露更多疏水区域，并且对蛋白酶消化更敏感。伴随着这些结构变化，氧化的PDIp还表现出增强的伴侣活性。PDIp中亚基间二硫键的形成主要由其非活性半胱氨酸残基（半胱氨酸-4）促成，该残基仅存在于人和灵长类动物的PDIp中，而不存在于啮齿动物的PDIp中。此外，我们观察到PDIp中亚基间二硫键的形成是氧化还原依赖性的，在氧化条件下更有利，并且PDIp可以作为伴侣与各种非天然细胞蛋白形成稳定复合物，特别是在氧化条件下。根据这些观察结果，得出结论：人PDIp的结构和功能通过两个半胱氨酸-4残基之间形成亚基间二硫键而受到氧化还原调节。
