Activation of the UPR sensor ATF6α is regulated by its redox-dependent dimerization and ER retention by ERp18.

SignificanceMembrane and secretory proteins are synthesized in the endoplasmic reticulum (ER). Perturbations to ER function disrupts protein folding, causing misfolded proteins to accumulate, a condition known as ER stress. Cells adapt to stress by activating the unfolded protein response (UPR), which ultimately restores proteostasis.

The mammalian cytosolic thioredoxin reductase pathway acts via a membrane protein to reduce ER-localised proteins.

Folding of proteins entering the mammalian secretory pathway requires the insertion of the correct disulfides. Disulfide formation involves both an oxidative pathway for their insertion and a reductive pathway to remove incorrectly formed disulfides. Reduction of these disulfides is crucial for correct folding and degradation of misfolded proteins.

ERp18 regulates activation of ATF6α during unfolded protein response.

Activation of the ATF6α signaling pathway is initiated by trafficking of ATF6α from the ER to the Golgi apparatus. Its subsequent proteolysis releases a transcription factor that translocates to the nucleus causing downstream gene activation. How ER retention, Golgi trafficking, and proteolysis of ATF6α are regulated and whether additional protein partners are required for its localization and processing remain unresolved.

Two essential Thioredoxins mediate apicoplast biogenesis, protein import, and gene expression in Toxoplasma gondii.

Apicomplexan parasites are global killers, being the causative agents of diseases like toxoplasmosis and malaria. These parasites are known to be hypersensitive to redox imbalance, yet little is understood about the cellular roles of their various redox regulators. The apicoplast, an essential plastid organelle, is a verified apicomplexan drug target.

Cytosolic thioredoxin reductase 1 is required for correct disulfide formation in the ER.

Folding of proteins entering the secretory pathway in mammalian cells frequently requires the insertion of disulfide bonds. Disulfide insertion can result in covalent linkages found in the native structure as well as those that are not, so-called non-native disulfides. The pathways for disulfide formation are well characterized, but our understanding of how non-native disulfides are reduced so that the correct or native disulfides can form is poor.

Thiol-disulfide exchange between the PDI family of oxidoreductases negates the requirement for an oxidase or reductase for each enzyme.

The formation of disulfides in proteins entering the secretory pathway is catalysed by the protein disulfide isomerase (PDI) family of enzymes. These enzymes catalyse the introduction, reduction and isomerization of disulfides. To function continuously they require an oxidase to reform the disulfide at their active site.

Inactivation of mammalian Ero1α is catalysed by specific protein disulfide-isomerases.

Disulfide formation within the endoplasmic reticulum is a complex process requiring a disulfide exchange protein such as PDI (protein disulfide-isomerase) and a mechanism to form disulfides de novo. In mammalian cells, the major pathway for de novo disulfide formation involves the enzyme Ero1α (endoplasmic reticulum oxidase 1α) which couples oxidation of thiols to the reduction of molecular oxygen to form hydrogen peroxide (H2O2). Ero1α activity is tightly regulated by a mechanism that requires the formation of regulatory disulfides.

ERdj5 is the ER reductase that catalyzes the removal of non-native disulfides and correct folding of the LDL receptor.

ERdj5 is a member of the protein disulfide isomerase family of proteins localized to the endoplasmic reticulum (ER) of mammalian cells. To date, only a limited number of substrates for ERdj5 are known. Here we identify a number of endogenous substrates that form mixed disulfides with ERdj5, greatly expanding its client repertoire.

Forming disulfides in the endoplasmic reticulum.

Protein disulfide bonds are an important co- and post-translational modification for proteins entering the secretory pathway. They are covalent interactions between two cysteine residues which support structural stability and promote the assembly of multi-protein complexes. In the mammalian endoplasmic reticulum (ER), disulfide bond formation is achieved by the combined action of two types of enzyme: one capable of forming disulfides de novo and another able to introduce these disulfides into substrates.

Interaction of the transactivation domain of B-Myb with the TAZ2 domain of the coactivator p300: molecular features and properties of the complex.

The transcription factor B-Myb is a key regulator of the cell cycle in vertebrates, with activation of transcription involving the recognition of specific DNA target sites and the recruitment of functional partner proteins, including the coactivators p300 and CBP. Here we report the results of detailed studies of the interaction between the transactivation domain of B-Myb (B-Myb TAD) and the TAZ2 domain of p300. The B-Myb TAD was characterized using circular dichroism, fluorescence and NMR spectroscopy, which revealed that the isolated domain exists as a random coil polypeptide.

Structure of the tandem MA-3 region of Pdcd4 protein and characterization of its interactions with eIF4A and eIF4G: molecular mechanisms of a tumor suppressor.

One of the key regulatory points of translation initiation is recruitment of the 43S preinitation complex to the 5' mRNA cap by the eIF4F complex (eIF4A, eIF4E, and eIF4G). The tumor suppressor protein Pdcd4 has been shown to inhibit cap-dependent translation by interacting tightly with the RNA helicase eIF4A via its tandem MA-3 domains. The NMR studies reported here reveal a fairly extensive and well defined interface between the two MA-3 domains in solution, which appears to be stabilized by a network of interdomain salt bridges and hydrogen bonds, and reveals a unique orientation of the two domains.

The reduction potential of the active site disulfides of human protein disulfide isomerase limits oxidation of the enzyme by Ero1α.

Disulfide formation in newly synthesized proteins entering the mammalian endoplasmic reticulum is catalyzed by protein disulfide isomerase (PDI), which is itself thought to be directly oxidized by Ero1α. The activity of Ero1α is tightly regulated by the formation of noncatalytic disulfides, which need to be broken to activate the enzyme. Here, we have developed a novel PDI oxidation assay, which is able to simultaneously determine the redox status of the individual active sites of PDI.

Resonance assignment and secondary structure of the middle MA-3 domain and complete tandem MA-3 region of the tumour suppressor protein Pdcd4.

Pdcd4 (Programmed Cell Death Protein 4) is a novel eukaryotic tumour suppressor protein, which is involved in the regulation of both transcription and translation (reviewed in Lankat-Buttgereit and Göke 2009). The protein contains two interacting MA-3 domains (MA-3(M) and MA-3(C)), which are linked by a short semi-flexible linker region (Waters et al. 2007; Suzuki et al.