Cooperation of ER-60 and BiP in the Oxidative Refolding of Denatured Proteins In Vitro

Insights into the role of ERp57 in cancer

Endoplasmic reticulum resident protein 57 (ERp57) has a molecular weight of 57 kDa, belongs to the protein disulfide-isomerase (PDI) family, and is primarily located in the endoplasmic reticulum (ER). ERp57 functions in the quality control of nascent synthesized glycoproteins, participates in major histocompatibility complex (MHC) class I molecule assembly, regulates immune responses, maintains immunogenic cell death (ICD), regulates the unfolded protein response (UPR), functions as a 1,25-dihydroxy vitamin D3 (1,25(OH)2D3) receptor, regulates the NF-κB and STAT3 pathways, and participates in DNA repair processes and cytoskeletal remodeling. Recent studies have reported ERp57 overexpression in various human cancers, and altered expression and aberrant functionality of ERp57 are associated with cancer growth and progression and changes in the chemosensitivity of cancers. ERp57 may become a potential biomarker and therapeutic target to combat cancer development and chemoresistance. Here, we summarize the available knowledge of the role of ERp57 in cancer and the underlying mechanisms.

Assessing the contribution of the two protein disulfide isomerases PDIA1 and PDIA3 to cisplatin resistance

Intracellular binding of cisplatin to non-DNA partners, such as proteins, has received increasing attention as an additional mode of action and as mechanism of resistance. We investigated two cisplatin-interacting isoforms of protein disulfide isomerase regarding their contribution to acquired cisplatin resistance using sensitive and resistant A2780/A2780cis ovarian cancer cells. Cisplatin cytotoxicity was assessed after knockdown of either protein disulfide isomerase family A member 1 (PDIA1) or protein disulfide isomerase family A member 3 (PDIA3). Whereas PDIA1 knockdown led to increased cytotoxicity in resistant A2780cis cells, PDIA3 knockdown showed no influence on cytotoxicity. Coincubation with propynoic acid carbamoyl methyl amide 31 (PACMA31), a PDIA1 inhibitor, resensitized A2780cis cells to cisplatin treatment. Determination of the combination index revealed that the combination of cisplatin and PACMA31 acts synergistically. Our results warrant further evaluation of PDIA1 as promising target for chemotherapy, and its inhibition by PACMA31 as a new therapeutic approach.

Modulation of conotoxin structure and function is achieved through a multienzyme complex in the venom glands of cone snails

The oxidative folding of large polypeptides has been investigated in detail; however, comparatively little is known about the enzyme-assisted folding of small, disulfide-containing peptide substrates. To investigate the concerted effect of multiple enzymes on the folding of small disulfide-rich peptides, we sequenced and expressed protein-disulfide isomerase (PDI), peptidyl-prolyl cis-trans isomerase, and immunoglobulin-binding protein (BiP) from Conus venom glands. Conus PDI was shown to catalyze the oxidation and reduction of disulfide bonds in two conotoxins, α-GI and α-ImI. Oxidative folding rates were further increased in the presence of Conus PPI with the maximum effect observed in the presence of both enzymes. In contrast, Conus BiP was only observed to assist folding in the presence of microsomes, suggesting that additional co-factors were involved. The identification of a complex between BiP, PDI, and nascent conotoxins further suggests that the folding and assembly of conotoxins is a highly regulated multienzyme-assisted process. Unexpectedly, all three enzymes contributed to the folding of the ribbon isomer of α-ImI. Here, we identify this alternative disulfide-linked species in the venom of Conus imperialis, providing the first evidence for the existence of a "non-native" peptide isomer in the venom of cone snails. Thus, ER-resident enzymes act in concert to accelerate the oxidative folding of conotoxins and modulate their conformation and function by reconfiguring disulfide connectivities. This study has evaluated the role of a number of ER-resident enzymes in the folding of conotoxins, providing novel insights into the enzyme-guided assembly of these small, disulfide-rich peptides.

Molecular Mechanisms of Cytotoxicity and Apoptosis Induced by Inorganic Fluoride

Fluoride (F) is ubiquitous natural substance and widespread industrial pollutant. Although low fluoride concentrations are beneficial for normal tooth and bone development, acute or chronic exposure to high fluoride doses results in adverse health effects. The molecular mechanisms underlying fluoride toxicity are different by nature. Fluoride is able to stimulate G-proteins with subsequent activation of downstream signal transduction pathways such as PKA-, PKC-, PI3-kinase-, Ca2+-, and MAPK-dependent systems. G-protein-independent routes include tyrosine phosphorylation and protein phosphatase inhibition. Along with other toxic effects, fluoride was shown to induce oxidative stress leading to excessive generation of ROS, lipid peroxidation, decrease in the GSH/GSSH ratio, and alterations in activities of antioxidant enzymes, as well as to inhibit glycolysis thus causing the depletion of cellular ATP and disturbances in cellular metabolism. Fluoride triggers the disruption of mitochondria outer membrane and release of cytochrome c into cytosol, what activates caspases-9 and -3 (intrinsic) apoptotic pathway. Extrinsic (death receptor) Fas/FasL-caspase-8 and -3 pathway was also described to be implicated in fluoride-induced apoptosis. Fluoride decreases the ratio of antiapoptotic/proapoptotic Bcl-2 family proteins and upregulates the expression of p53 protein. Finally, fluoride changes the expression profile of apoptosis-related genes and causes endoplasmic reticulum stress leading to inhibition of protein synthesis.

Molecular cloning and characterization of soybean protein disulfide isomerase family proteins with nonclassic active center motifs

Protein disulfide isomerase (PDI) and other PDI family proteins are members of the thioredoxin superfamily and are thought to play important roles in disulfide bond formation and isomerization in the endoplasmic reticulum (ER). The exact functions of PDI family proteins in plants remain unknown. In this study, we cloned two novel PDI family genes from soybean leaf (Glycine max L. Merrill cv. Jack). The cDNAs encode proteins of 520 and 523 amino acids, and have been denoted GmPDIL-3a and GmPDIL-3b, respectively. GmPDIL-3a and GmPDIL-3b are the first plant ER PDI family proteins reported to contain the nonclassic redox center motif CXXS/C, and both proteins are ubiquitously expressed in the plant body. However, recombinant GmPDIL-3a and GmPDIL-3b did not function as oxidoreductases or as molecular chaperones in vitro, although a proportion of each protein formed complexes in both thiol-dependent and thiol-independent ways in the ER. Expression of GmPDIL-3a and GmPDIL-3b in the cotyledon increased during seed maturation when synthesis of storage proteins was initiated. These results suggest that GmPDIL-3a and GmPDIL-3b may play important roles in the maturation of the cotyledon by mechanisms distinct from those of other PDI family proteins.

Dynamic redox environment-intensified disulfide bond shuffling for protein refolding in vitro: molecular simulation and experimental validation

One challenge in protein refolding is to dissociate the non-native disulfide bonds and promote the formation of native ones. In this study, we present a coarse-grained off-lattice model protein containing disulfide bonds and simulate disulfide bond shuffling during the folding of this model protein. Introduction of disulfide bonds in the model protein led to enhanced conformational stability but reduced foldability in comparison to counterpart protein without disulfide bonds. The folding trajectory suggested that the model protein retained the two-step folding mechanism in terms of hydrophobic collapse and structural rearrangement. The disulfide bonds located in the hydrophobic core were formed before the collapsing step, while the bonds located on the protein surface were formed during the rearrangement step. While a reductive environment at the initial stage of folding favored the formation of native disulfide bonds in the hydrophobic core, an oxidative environment at a later stage of folding was required for the formation of disulfide bonds at protein surface. Appling a dynamic redox environment, that is, one that changes from reductive to oxidative, intensified disulfide bond shuffling and thus resulted in improved recovery of the native conformation. The above-mentioned simulation was experimentally validated by refolding hen-egg lysozyme at different urea concentrations and oxidized glutathione/reduced glutathione (GSSG/GSH) ratios, and an optimal redox environment, in terms of the GSSG to GSH ratio, was identified. The implementation of a dynamic redox environment by tuning the GSSG/GSH ratio further improved the refolding yield of lysozyme, as predicted by molecular simulation.

Survey of the year 2005 commercial optical biosensor literature

We identified 1113 articles (103 reviews, 1010 primary research articles) published in 2005 that describe experiments performed using commercially available optical biosensors. While this number of publications is impressive, we find that the quality of the biosensor work in these articles is often pretty poor. It is a little disappointing that there appears to be only a small set of researchers who know how to properly perform, analyze, and present biosensor data. To help focus the field, we spotlight work published by 10 research groups that exemplify the quality of data one should expect to see from a biosensor experiment. Also, in an effort to raise awareness of the common problems in the biosensor field, we provide side-by-side examples of good and bad data sets from the 2005 literature.