Project description:The protein secretory pathway must maintain homoeostasis while producing a wide assortment of proteins in different conditions. It is also used extensively to produce many useful proteins in biotechnology. As such, secretory pathway dysfunction can be highly detrimental to the cell, resulting in the molecular basis for many human diseases, and can drastically inhibit product titers in biochemical production. Because the secretory pathway is a highly-integrated, multi-organelle system, dysfunction can happen at many levels and dissecting the root cause can be challenging. To better understand some of these dysfunctions, we measured multiple systems-level states of the cell (physiology, transcriptome, metabolism) while secreting a small protein (insulin precursor) or a large protein (?-amylase). This was carried out in the presence and absence of HAC1, a key transcription factor in maintaining secretory homeostasis. Clear trends in cellular stress were apparent across multiple data resulting from our perturbations. In particular, processes involving (1) degradation of protein / recycling amino acids, (2) overall transcription/translation repression, and (3) oxidative stress. Apparent runaway oxidative radical production was explained by a thermodynamic model that we put forward for disulfide formation in the endoplasmic reticulum. This model predicts that balancing the relative rates of protein folding and disulfide bond formation are key to easing oxidative stress. These predictions have direct implications in how to engineer a broad range of recombinant proteins for secretion and provide potential hypotheses for the root causes of several secretory-associated diseases. Yeast strains were constructed that produce and secrete (a) IP or (b) ?-amylase and were compared to yeast strains containing (c) an empty vector in both wild-type and HAC1 deletion backgrounds. These strains are named WN (WT with empty vector), WI (WT secreting IP), WA (WT secreting ?-amylase), dN (?hac1 with empty vector), dI (?hac1 secreting IP), and dA (?hac1 secreting ?-amylase). Strains were characterized in batch fermentation and samples were taken in mid-exponential phase. Triplicate fermentations were carried out for each strain.
Project description:The protein secretory pathway must maintain homoeostasis while producing a wide assortment of proteins in different conditions. It is also used extensively to produce many useful proteins in biotechnology. As such, secretory pathway dysfunction can be highly detrimental to the cell, resulting in the molecular basis for many human diseases, and can drastically inhibit product titers in biochemical production. Because the secretory pathway is a highly-integrated, multi-organelle system, dysfunction can happen at many levels and dissecting the root cause can be challenging. To better understand some of these dysfunctions, we measured multiple systems-level states of the cell (physiology, transcriptome, metabolism) while secreting a small protein (insulin precursor) or a large protein (α-amylase). This was carried out in the presence and absence of HAC1, a key transcription factor in maintaining secretory homeostasis. Clear trends in cellular stress were apparent across multiple data resulting from our perturbations. In particular, processes involving (1) degradation of protein / recycling amino acids, (2) overall transcription/translation repression, and (3) oxidative stress. Apparent runaway oxidative radical production was explained by a thermodynamic model that we put forward for disulfide formation in the endoplasmic reticulum. This model predicts that balancing the relative rates of protein folding and disulfide bond formation are key to easing oxidative stress. These predictions have direct implications in how to engineer a broad range of recombinant proteins for secretion and provide potential hypotheses for the root causes of several secretory-associated diseases.
Project description:Understanding the conformational sampling of translation-arrested ribosome nascent chain complexes is key to understand co-translational folding. Up to now, coupling of cysteine oxidation, disulfide bond formation and structure formation in nascent chains has remained elusive. Here, we investigate the eye-lens protein γB-crystallin in the ribosomal exit tunnel. Using mass spectrometry, theoretical simulations, dynamic nuclear polarization-enhanced solid-state nuclear magnetic resonance and cryo-electron microscopy, we show that thiol groups of cysteine residues undergo S-glutathionylation and S-nitrosylation and form non-native disulfide bonds. Thus, covalent modification chemistry occurs already prior to nascent chain release as the ribosome exit tunnel provides sufficient space even for disulfide bond formation which can guide protein folding.
Project description:N-glycosylation and disulfide bond formation are two essential steps in protein folding, that both take place in the endoplasmic reticulum (ER). These two modifications can influence each other, but the exact timing, as well as the mediators of this important crosstalk, are still not completely elucidated. In previous work, we demonstrated that cells deficient in ER oxidoreductin 1-alpha (ERO1-alpha), a protein disulfide oxidase, are impaired in their ability to secrete Vascular Endothelial Growth Factor-A (VEGF121), a key regulator of vascular homeostasis in health and of metastasis in cancer. Here, to analyze the crosstalk between N-glycosylation and disulfide bond formation in newly synthesized proteins of the ER, we investigated how ERO1-alpha deficit affects glycosylation of VEGF121. We found that reduced ER redox poise imposed by ERO1 deficiency, while slowing down the intracellular formation of disulfide-bonds in VEGF121, promoted the full utilization of its single N-glycosylation consensus site, which lies close to an intra-polypeptide disulfide bridge. Unexpectedly, this hyperglycosylation impairs the kinetics of VEGF121 secretion. Unbiased mass-spectrometric data of VEGF121 immunoprecipitates followed by pathway analysis indicated a stable interaction between VEGF121 and proteins involved in the N-glycosylation in ERO1-alpha knockout, but not wild-type cells. Notably, MAGT1, a thioredoxin-containing protein and part of the post-translational oligosaccharyltransferase complex (OST), was a major hit exclusive to ERO1-deficient cells. We demonstrate that post-translational N-glycosylation VEGF121 is increased under the altered redox poise caused by ERO1 deficit: on the one hand by a reduced rate of formation of its disulfide bridges, and on the other, by the increased trapping potential of MAGT1's thioredoxin domain. These findings have implications for a variety of pathological processes involving altered redox conditions in the ER.
Project description:Endoplasmic reticulum (ER) thiol oxidases initiate a disulfide relay to oxidatively-fold secreted proteins. We found that combined loss-of-function mutations in genes encoding the ER thiol oxidases ERO1alpha, ERO1beta and PRDX4, compromised the extracellular matrix in mice and interfered with the intracellular maturation of procollagen. These severe abnormalities were associated with an unexpectedly-modest delay in disulfide bond formation in secreted proteins but a profound, five-fold lower procollagen 4 hydroxyproline content and enhanced cysteinyl sulfenic acid modification of ER proteins. Tissue ascorbic acid content was lower in mutant mice and ascorbic acid supplementation improved procollagen maturation and lowered sulfenic acid content, in vivo. In vitro, the presence of a sulfenic acid donor accelerated the oxidative inactivation of ascorbate by an H2O2 generating system. Compromised ER disulfide relay thus exposes protein thiols to competing oxidation to sulfenic acid, resulting in depletion of ascorbic acid, impaired procollagen proline 4-hydroxylation and a non-canonical form of scurvy. double and triple mutants and wild type
Project description:E. coli CyDisCo strain enables a high yield secretion of disulfide bond-containing proteins to the periplasm via Twin-arginine (Tat) pathway. Introducing two exogenous oxidases: the yeast sulfydryl oxidase (Erv1p) and human protein disulfide isomerase (PDI), the CyDisCo strain changes the cytoplasm into an oxidized environment, where the disulfide bonds can efficiently be formed. In this study, we analyzed the proteome changes upon the expression of disulfide bond-containing scFv and the misfolded scFv in the CyDisCo strain. The correctly folded protein is secreted to the periplasm, while the misfolded protein accumulates exclusively in the inclusion body fraction. We observed a high number of significant changes mostly in proteins associated with protein folding and degradation, oxidative stress, membrane transport and integrity.
Project description:Protein disulfide isomerases (PDIs) aid protein folding and assembly by catalyzing formation and shuffling of cysteine disulfide bonds in the endoplasmic reticulum (ER). Many members of the PDI family are expressed in mammals but the roles of specific PDIs in vivo are poorly understood. A recent homology-based search for additional PDI family members identified anterior gradient homolog 2 (AGR2), a protein originally presumed to be secreted by intestinal epithelial cells, but the function of AGR2 has been obscure. Here we show that AGR2 is expressed in the ER of secretory cells and is essential for in vivo production of intestinal mucin, a large cysteine-rich glycoprotein that forms the protective mucus gel lining the intestine. A cysteine residue within the AGR2 thioredoxin-like domain forms mixed disulfide bonds with MUC2, consistent with a direct role for AGR2 in mucin processing. Despite a complete absence of intestinal mucin, mice lacking AGR2 appeared healthy but were highly susceptible to dextran sodium sulfate-induced experimental colitis, indicating a critical role for AGR2 in protection from environmental insults. We conclude that AGR2 is a unique member of the PDI family that has a specialized and non-redundant role in intestinal mucus production. Keywords: small intestine and colon gene expression profiles for Agr2-/- and littermate control mice DNA miocroarrays were used to analyze small intenstine and colon mRNA expression of AGR2 KO and littermate control mice. The experiment incorporated a 1 color design and used Agilent arrays that contained roughly 44,00 60mer probes that provide complete coverage of the mouse genome. 12 arrays were hybridized and represent 8 small intestine samples ( 4 each KO and WT) and 4 colon samples (2 each KO and WT)
Project description:Protein disulfide isomerases (PDIs) aid protein folding and assembly by catalyzing formation and shuffling of cysteine disulfide bonds in the endoplasmic reticulum (ER). Many members of the PDI family are expressed in mammals but the roles of specific PDIs in vivo are poorly understood. A recent homology-based search for additional PDI family members identified anterior gradient homolog 2 (AGR2), a protein originally presumed to be secreted by intestinal epithelial cells, but the function of AGR2 has been obscure. Here we show that AGR2 is expressed in the ER of secretory cells and is essential for in vivo production of intestinal mucin, a large cysteine-rich glycoprotein that forms the protective mucus gel lining the intestine. A cysteine residue within the AGR2 thioredoxin-like domain forms mixed disulfide bonds with MUC2, consistent with a direct role for AGR2 in mucin processing. Despite a complete absence of intestinal mucin, mice lacking AGR2 appeared healthy but were highly susceptible to dextran sodium sulfate-induced experimental colitis, indicating a critical role for AGR2 in protection from environmental insults. We conclude that AGR2 is a unique member of the PDI family that has a specialized and non-redundant role in intestinal mucus production. Keywords: small intestine and colon gene expression profiles for Agr2-/- and littermate control mice
Project description:Endoplasmic reticulum (ER) thiol oxidases initiate a disulfide relay to oxidatively-fold secreted proteins. We found that combined loss-of-function mutations in genes encoding the ER thiol oxidases ERO1alpha, ERO1beta and PRDX4, compromised the extracellular matrix in mice and interfered with the intracellular maturation of procollagen. These severe abnormalities were associated with an unexpectedly-modest delay in disulfide bond formation in secreted proteins but a profound, five-fold lower procollagen 4 hydroxyproline content and enhanced cysteinyl sulfenic acid modification of ER proteins. Tissue ascorbic acid content was lower in mutant mice and ascorbic acid supplementation improved procollagen maturation and lowered sulfenic acid content, in vivo. In vitro, the presence of a sulfenic acid donor accelerated the oxidative inactivation of ascorbate by an H2O2 generating system. Compromised ER disulfide relay thus exposes protein thiols to competing oxidation to sulfenic acid, resulting in depletion of ascorbic acid, impaired procollagen proline 4-hydroxylation and a non-canonical form of scurvy.
Project description:Folding of proteins entering the mammalian secretory pathway requires the insertion of the correct disulfide bonds. Disulfide formation involves both an oxidative pathway for their insertion and a reductive pathway to remove incorrectly formed disulfides. Reduction of these disulfides is critical for correct folding and degradation of misfolded proteins. Previously, we showed that the reductive pathway is driven by NADPH generated in the cytosol. Here, by reconstituting the pathway using purified proteins and ER microsomal membranes, we demonstrate that the thioredoxin reductase system provides the minimal cytosolic components required for reducing proteins within the ER lumen. In particular, saturation of the pathway and its protease sensitivity demonstrates the requirement for a membrane protein to shuttle electrons from the cytosol to the ER lumen. These results provide compelling evidence for the critical role of the cytosol in regulating ER redox homeostasis to ensure correct protein folding and to facilitate the degradation of misfolded ER proteins.