Effects of pH and Salt Concentration on Stability of a Protein G Variant Using Coarse-Grained Models

The importance of charge-charge interactions in the thermal stability of proteins is widely known. pH and ionic strength play a crucial role in these electrostatic interactions, as well as in the arrangement of ionizable residues in each protein-folding stage. In this study, two coarse-grained models were used to evaluate the effect of pH and salt concentration on the thermal stability of a protein G variant (1PGB-QDD), which was chosen due to the quantity of experimental data exploring these effects on its stability. One of these coarse-grained models, the TKSA, calculates the electrostatic free energy of the protein in the native state via the Tanford-Kirkwood approach for each residue. The other one, CpHMD-SBM, uses a Coulomb screening potential in addition to the structure-based model Cα. Both models simulate the system in constant pH. The comparison between the experimental stability analysis and the computational results obtained by these simple models showed a good agreement. Through the TKSA method, the role of each charged residue in the protein's thermal stability was inferred. Using CpHMD-SBM, it was possible to evaluate salt and pH effects throughout the folding process. Finally, the computational pKa values were calculated by both methods and presented a good level of agreement with the experiments. This study provides, to our knowledge, new information and a comprehensive description of the electrostatic contribution to protein G stability.

Lipophilicity of the Cystic Fibrosis Drug, Ivacaftor (VX-770), and Its Destabilizing Effect on the Major CF-causing Mutation: F508del

Deletion of phenylalanine at position 508 (F508del) in cystic fibrosis transmembrane conductance regulator (CFTR) is the most common cystic fibrosis (CF)-causing mutation. Recently, ORKAMBI, a combination therapy that includes a corrector of the processing defect of F508del-CFTR (lumacaftor or VX-809) and a potentiator of channel activity (ivacaftor or VX-770), was approved for CF patients homozygous for this mutation. However, clinical studies revealed that the effect of ORKAMBI on lung function is modest and it was proposed that this modest effect relates to a negative impact of VX-770 on the stability of F508del-CFTR. In the current studies, we showed that this negative effect of VX-770 at 10 μM correlated with its inhibitory effect on VX-809-mediated correction of the interface between the second membrane spanning domain and the first nucleotide binding domain bearing F508del. Interestingly, we found that VX-770 exerted a similar negative effect on the stability of other membrane localized solute carriers (SLC26A3, SLC26A9, and SLC6A14), suggesting that this negative effect is not specific for F508del-CFTR. We determined that the relative destabilizing effect of a panel of VX-770 derivatives on F508del-CFTR correlated with their predicted lipophilicity. Polarized total internal reflection fluorescence microscopy on a supported lipid bilayer model shows that VX-770, and not its less lipophilic derivative, increased the fluidity of and reorganized the membrane. In summary, our findings show that there is a potential for nonspecific effects of VX-770 on the lipid bilayer and suggest that this effect may account for its destabilizing effect on VX-809- rescued F508del-CFTR.

The flavonoid luteolin, but not luteolin-7-O-glucoside, prevents a transthyretin mediated toxic response

Transthyretin (TTR) is a homotetrameric plasma protein with amyloidogenic properties that has been linked to the development of familial amyloidotic polyneuropathy (FAP), familial amyloidotic cardiomyopathy, and senile systemic amyloidosis. The in vivo role of TTR is associated with transport of thyroxine hormone T4 and retinol-binding protein. Loss of the tetrameric integrity of TTR is a rate-limiting step in the process of TTR amyloid formation, and ligands with the ability to bind within the thyroxin binding site (TBS) can stabilize the tetramer, a feature that is currently used as a therapeutic approach for FAP. Several different flavonoids have recently been identified that impair amyloid formation. The flavonoid luteolin shows therapeutic potential with low incidence of unwanted side effects. In this work, we show that luteolin effectively attenuates the cytotoxic response to TTR in cultured neuronal cells and rescues the phenotype of a Drosophila melanogaster model of FAP. The plant-derived luteolin analogue cynaroside has a glucoside group in position 7 of the flavone A-ring and as opposed to luteolin is unable to stabilize TTR tetramers and thus prevents a cytotoxic effect. We generated high-resolution crystal-structures of both TTR wild type and the amyloidogenic mutant V30M in complex with luteolin. The results show that the A-ring of luteolin, in contrast to what was previously suggested, is buried within the TBS, consequently explaining the lack of activity from cynaroside. The flavonoids represent an interesting group of drug candidates for TTR amyloidosis. The present investigation shows the potential of luteolin as a stabilizer of TTR in vivo. We also show an alternative orientation of luteolin within the TBS which could represent a general mode of binding of flavonoids to TTR and is of importance concerning the future design of tetramer stabilizing drugs.

Identification of Ezetimibe and Pranlukast as Pharmacological Chaperones for the Treatment of the Rare Disease Mucopolysaccharidosis Type IVA

Mucopolysaccharidosis type IVA (MPS IVA) is a rare disease caused by mutations in the gene encoding the lysosomal enzyme N-acetylgalactosamine-6-sulfate sulfatase (GALNS). We report here two GALNS pharmacological chaperones, ezetimibe and pranlukast, identified by molecular docking-based virtual screening. These compounds bound to the active cavity of GALNS and increased its thermal stability as well as the production of recombinant GALNS in bacteria, yeast, and HEK293 cells. MPS IVA fibroblasts treated with these chaperones exhibited increases in GALNS protein and enzyme activity and reduced the size of enlarged lysosomes. Abnormalities in autophagy markers p62 and LC3B-II were alleviated by ezetimibe and pranlukast. Combined treatment of recombinant GALNS with ezetimibe or pranlukast produced an additive effect. Altogether, the results demonstrate that ezetimibe and pranlukast can increase the yield of recombinant GALNS and be used as a monotherapy or combination therapy to improve the therapeutic efficacy of MPS IVA enzyme replacement therapy.

The maize OST1 kinase homolog phosphorylates and regulates the maize SNAC1-type transcription factor

The Arabidopsis kinase OPEN STOMATA 1 (OST1) plays a key role in regulating drought stress signalling, particularly stomatal closure. We have identified and investigated the functions of the OST1 ortholog in Z. mays (ZmOST1). Ectopic expression of ZmOST1 in the Arabidopsis ost1 mutant restores the stomatal closure phenotype in response to drought. Furthermore, we have identified the transcription factor, ZmSNAC1, which is directly phosphorylated by ZmOST1 with implications on its localization and protein stability. Interestingly, ZmSNAC1 binds to the ABA-box of ZmOST1, which is conserved in SnRK2s activated by ABA and is part of the contact site for the negative-regulating clade A PP2C phosphatases. Taken together, our results indicate that ZmSNAC1 is a substrate of ZmOST1 and delineate a novel osmotic stress transcriptional pathway in maize.

The role of hypoxia-inducible factor stabilizers in the treatment of anemia in patients with chronic kidney disease

INTRODUCTION

The purpose of this study was to analyze the effects of hypoxia-inducible factor (HIF) stabilizers on anemia in non-dialysis-dependent (NDD) and dialysis-dependent (DD) chronic kidney disease (CKD) patients.

METHODS

Published studies were extracted from PubMed, China Biological Medicine Database (CBM), Wanfang database, and Cochrane Library on March 10, 2018, and relevant studies were pooled and included in a meta-analysis. Data on hemoglobin (Hb), ferritin, and hepcidin levels, total iron-binding capacity (TIBC), and incidence of adverse events (AEs) were extracted and pooled using Review Manager Version 5.3.

RESULTS

Data from nine selected studies were extracted. Meta-analysis of the included studies showed that HIF stabilizers reduced ferritin and hepcidin levels and increased Hb level and TIBC in NDD-CKD patients. However, HIF stabilizers only increased TIBC, and did not affect ferritin, hepcidin, and Hb levels in DD-CKD patients. Furthermore, no notable differences in AEs and severe AEs between NDD-CKD and DD-CKD patients were detected.

CONCLUSION

HIF stabilizers are effective for the treatment of anemia in NDD-CKD patients and safe for short-term use.

A spiroligomer α-helix mimic that binds HDM2, penetrates human cells and stabilizes HDM2 in cell culture

We demonstrate functionalized spiroligomers that mimic the HDM2-bound conformation of the p53 activation domain. Spiroligomers are stereochemically defined, functionalized, spirocyclic monomers coupled through pairs of amide bonds to create spiro-ladder oligomers [1]. Two series of spiroligomers were synthesized, one of structural analogs and one of stereochemical analogs, from which we identified compound 1, that binds HDM2 with a Kd value of 400 nM. The spiroligomer 1 penetrates human liver cancer cells through passive diffusion and in a dose-dependent and time-dependent manner increases the levels of HDM2 more than 30-fold in Huh7 cells in which the p53/HDM2 negative feed-back loop is inoperative. This is a biological effect that is not seen with the HDM2 ligand nutlin-3a. We propose that compound 1 modulates the levels of HDM2 by stabilizing it to proteolysis, allowing it to accumulate in the absence of a p53/HDM2 feedback loop.

β-catenin directly sequesters adipocytic and insulin sensitizing activities but not osteoblastic activity of PPARγ2 in marrow mesenchymal stem cells

Lineage allocation of the marrow mesenchymal stem cells (MSCs) to osteoblasts and adipocytes is dependent on both Wnt signaling and PPARγ2 activity. Activation of PPARγ2, an essential regulator of energy metabolism and insulin sensitivity, stimulates adipocyte and suppresses osteoblast differentiation and bone formation, and correlates with decreased bone mass and increased fracture rate. In contrast, activation of Wnt signaling promotes osteoblast differentiation, augments bone accrual and reduces total body fat. This study examined the cross-talk between PPARγ2 and β-catenin, a key mediator of canonical Wnt signaling, on MSC lineage determination. Rosiglitazone-activated PPARγ2 induced rapid proteolytic degradation of β-catenin, which was prevented by either inhibiting glycogen synthase kinase 3 beta (GSK3β) activity, or blocking pro-adipocytic activity of PPARγ2 using selective antagonist GW9662 or mutation within PPARγ2 protein. Stabilization of β-catenin suppressed PPARγ2 pro-adipocytic but not anti-osteoblastic activity. Moreover, β-catenin stabilization decreased PPARγ2-mediated insulin signaling as measured by insulin receptor and FoxO1 gene expression, and protein levels of phosphorylated Akt (pAkt). Cellular knockdown of β-catenin with siRNA increased expression of adipocyte but did not affect osteoblast gene markers. Interestingly, the expression of Wnt10b was suppressed by anti-osteoblastic, but not by pro-adipocytic activity of PPARγ2. Moreover, β-catenin stabilization in the presence of activated PPARγ2 did not restore Wnt10b expression indicating a dominant role of PPARγ2 in negative regulation of pro-osteoblastic activity of Wnt signaling. In conclusion, β-catenin and PPARγ2 are in cross-talk which results in sequestration of pro-adipocytic and insulin sensitizing activity. The anti-osteoblastic activity of PPARγ2 is independent of this interaction.

Novel Flavivirus Antiviral That Targets the Host Nuclear Transport Importin α/β1 Heterodimer

Dengue virus (DENV) threatens almost 70% of the world’s population, with no effective vaccine or therapeutic currently available. A key contributor to infection is nuclear localisation in the infected cell of DENV nonstructural protein 5 (NS5) through the action of the host importin (IMP) α/β1 proteins. Here, we used a range of microscopic, virological and biochemical/biophysical approaches to show for the first time that the small molecule GW5074 has anti-DENV action through its novel ability to inhibit NS5–IMPα/β1 interaction in vitro as well as NS5 nuclear localisation in infected cells. Strikingly, GW5074 not only inhibits IMPα binding to IMPβ1, but can dissociate preformed IMPα/β1 heterodimer, through targeting the IMPα armadillo (ARM) repeat domain to impact IMPα thermal stability and α-helicity, as shown using analytical ultracentrifugation, thermostability analysis and circular dichroism measurements. Importantly, GW5074 has strong antiviral activity at low µM concentrations against not only DENV-2, but also zika virus and West Nile virus. This work highlights DENV NS5 nuclear targeting as a viable target for anti-flaviviral therapeutics.

Coupling of the non-amyloid-component (NAC) domain and the KTK(E/Q)GV repeats stabilize the α-synuclein fibrils

The aggregates of α-synuclein (αS) are a major pathological hallmark of Parkinson's disease (PD) making their structure-function relationship important for rational drug design. Yet, the atomic structure of the αS aggregates is unavailable, making it difficult to understand the underlying aggregation mechanism. In this work, based on available experimental data, we examined plausible molecular structures of αS(20/30-110) fibrils for the first time by employing computational approaches. The optimized structure was used to investigate possible interactions with aggregation inhibitors. Our structural models characterize the essential properties of the five-layered fold of the αS fibril. The distribution of the β-strands and the topology of the five β-strands in the relatively stable models are in good agreement with experimental values. In particular, we find that the KTK(E/Q)GV repeat motifs significantly stabilize the αS fibrils. The charged residues within each repeat prefer exposure to the solvent in order to further stabilize the inter-layered interactions by salt-bridges. The organization of the repeat K(58)T(59)K(60)E(61)Q(62)V(63) between the β2 and β3 layers significantly affects the stability of the non-amyloid-component (NAC) domain. The coupling between the NAC domain and the KTKEGV repeats indicates that both regions can be potential binding sites for inhibitor design. The distinct binding modes of chemical agents that alter αS aggregation highlight the potential of our models in inhibitor design.

Eltrombopag directly inhibits BAX and prevents cell death

The BCL-2 family protein BAX has essential activity in mitochondrial regulation of cell death. While BAX activity ensures tissue homeostasis, when dysregulated it contributes to aberrant cell death in several diseases. During cellular stress BAX is transformed from an inactive cytosolic conformation to a toxic mitochondrial oligomer. Although the BAX transformation process is not well understood, drugs that interfere with this process are useful research tools and potential therapeutics. Here, we show that Eltrombopag,  an FDA-approved drug,  is a direct inhibitor of BAX. Eltrombopag binds the BAX trigger site distinctly from BAX activators, preventing them from triggering BAX conformational transformation and simultaneously promoting stabilization of the inactive BAX structure. Accordingly, Eltrombopag is capable of inhibiting BAX-mediated apoptosis induced by cytotoxic stimuli. Our data demonstrate structure-function insights into a mechanism of BAX inhibition and reveal a mechanism for Eltrombopag that may expand its use in diseases of uncontrolled cell death.

The Antarctic Psychrophile Chlamydomonas sp. UWO 241 Preferentially Phosphorylates a Photosystem I-Cytochrome b6/f Supercomplex

Chlamydomonas sp. UWO 241 (UWO 241) is a psychrophilic green alga isolated from Antarctica. A unique characteristic of this algal strain is its inability to undergo state transitions coupled with the absence of photosystem II (PSII) light-harvesting complex protein phosphorylation. We show that UWO 241 preferentially phosphorylates specific polypeptides associated with an approximately 1,000-kD pigment-protein supercomplex that contains components of both photosystem I (PSI) and the cytochrome b₆/f (Cyt b₆/f) complex. Liquid chromatography nano-tandem mass spectrometry was used to identify three major phosphorylated proteins associated with this PSI-Cyt b₆/f supercomplex, two 17-kD PSII subunit P-like proteins and a 70-kD ATP-dependent zinc metalloprotease, FtsH. The PSII subunit P-like protein sequence exhibited 70.6% similarity to the authentic PSII subunit P protein associated with the oxygen-evolving complex of PSII in Chlamydomonas reinhardtii. Tyrosine-146 was identified as a unique phosphorylation site on the UWO 241 PSII subunit P-like polypeptide. Assessment of PSI cyclic electron transport by in vivo P700 photooxidation and the dark relaxation kinetics of P700(+) indicated that UWO 241 exhibited PSI cyclic electron transport rates that were 3 times faster and more sensitive to antimycin A than the mesophile control, Chlamydomonas raudensis SAG 49.72. The stability of the PSI-Cyt b₆/f supercomplex was dependent upon the phosphorylation status of the PsbP-like protein and the zinc metalloprotease FtsH as well as the presence of high salt. We suggest that adaptation of UWO 241 to its unique low-temperature and high-salt environment favors the phosphorylation of a PSI-Cyt b₆/f supercomplex to regulate PSI cyclic electron transport rather than the regulation of state transitions through the phosphorylation of PSII light-harvesting complex proteins.

Human Serum Albumin Adsorption Kinetics on Silica: Influence of Protein Solution Stability

Adsorption kinetics of human serum albumin (HSA) on silica substrates was studied using optical waveguide lightmode spectroscopy (OWLS) and quartz microbalance (QCM) techniques. Measurements were performed at pH 3.5, 5.6, and 7.4 for various bulk suspension concentrations and ionic strengths. The diffusion coefficient measurements showed that for pH 3.5 the HSA molecules are stable for NaCl concentrations from 10^-3 to 0.15 M. This allowed us to precisely determine the mass transfer rate coefficients for the OWLS and QCM cells. The experimental data were adequately interpreted in terms of a hybrid random sequential adsorption model. The OWLS maximum coverage of HSA at pH 3.5, which is equal to 1.3 mg m^-2, agrees with the QCM result and with previous results derived from streaming potential measurements. Thus, the results obtained at pH 3.5 served as reference data for the analysis of adsorption kinetics at higher pHs. In this way, it was confirmed that the adsorption kinetics of HSA molecules at pH 5.6 and 7.4 was considerably slower than at pH 3.5. This effect was attributed to aggregation of HSA solutions and interpreted in terms of a theoretical model combining the Smoluchowski aggregation theory with the convective diffusion mass transfer theory. New analytical equations were derived that can be used for the interpretation of other protein adsorption from unstable solutions.

Actin stabilization by jasplakinolide affects the function of bone marrow-derived late endothelial progenitor cells

Background

Bone marrow-derived endothelial progenitor cells (EPCs), especially late EPCs, play a critical role in endothelial maintenance and repair, and postnatal vasculogenesis. Although the actin cytoskeleton has been considered as a modulator that controls the function and modulation of stem cells, its role in the function of EPCs, and in particular late EPCs, remains poorly understood.

Methodology/Principal Finding

Bone marrow-derived late EPCs were treated with jasplakinolide, a compound that stabilizes actin filaments. Cell apoptosis, proliferation, adhesion, migration, tube formation, nitric oxide (NO) production and endothelial NO synthase (eNOS) phosphorylation were subsequently assayed in vitro. Moreover, EPCs were locally infused into freshly balloon-injured carotid arteries, and the reendothelialization capacity was evaluated after 14 days. Jasplakinolide affected the actin distribution of late EPCs in a concentration and time dependent manner, and a moderate concentration of (100 nmol/l) jasplakinolide directly stabilized the actin filament of late EPCs. Actin stabilization by jasplakinolide enhanced the late EPC apoptosis induced by VEGF deprivation, and significantly impaired late EPC proliferation, adhesion, migration and tube formation. Furthermore, jasplakinolide attenuated the reendothelialization capacity of transplanted EPCs in the injured arterial segment in vivo. However, eNOS phosphorylation and NO production were increased in late EPCs treated with jasplakinolide. NO donor sodium nitroprusside (SNP) rescued the functional activities of jasplakinolide-stressed late EPCs while the endothelial NO synthase inhibitor L-NAME led to a further dysfunction induced by jasplakinolide in late EPCs.

Conclusions/Significance

A moderate concentration of jasplakinolide results in an accumulation of actin filaments, enhancing the apoptosis induced by cytokine deprivation, and impairing the proliferation and function of late EPCs both in vitro and in vivo. NO donor reverses these impairments, suggesting the role of NO-related mechanisms in jasplakinolide-induced EPC downregulation. Actin cytoskeleton may thus play a pivotal role in regulating late EPC function.

ZmABA2, an interacting protein of ZmMPK5, is involved in abscisic acid biosynthesis and functions

In maize (Zea mays), the mitogen-activated protein kinase ZmMPK5 has been shown to be involved in abscisic acid (ABA)-induced antioxidant defence and to enhance the tolerance of plants to drought, salt stress and oxidative stress. However, the underlying molecular mechanisms are poorly understood. Here, using ZmMPK5 as bait in yeast two-hybrid screening, a protein interacting with ZmMPK5 named ZmABA2, which belongs to a member of the short-chain dehydrogenase/reductase family, was identified. Pull-down assay and bimolecular fluorescence complementation analysis and co-immunoprecipitation test confirmed that ZmMPK5 interacts with ZmABA2 in vitro and in vivo. Phosphorylation of Ser173 in ZmABA2 by ZmMPK5 was shown to increase the activity of ZmABA2 and the protein stability. Various abiotic stimuli induced the expression of ZmABA2 in leaves of maize plants. Pharmacological, biochemical and molecular biology and genetic analyses showed that both ZmMPK5 and ZmABA2 coordinately regulate the content of ABA. Overexpression of ZmABA2 in tobacco plants was found to elevate the content of ABA, regulate seed germination and root growth under drought and salt stress and enhance the tolerance of tobacco plants to drought and salt stress. These results suggest that ZmABA2 is a direct target of ZmMPK5 and is involved in ABA biosynthesis and functions.

MPT0B098, a Microtubule Inhibitor, Suppresses JAK2/STAT3 Signaling Pathway through Modulation of SOCS3 Stability in Oral Squamous Cell Carcinoma

Microtubule inhibitors have been shown to inhibit Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) signal transduction pathway in various cancer cells. However, little is known of the mechanism by which the microtubule inhibitors inhibit STAT3 activity. In the present study, we examined the effect of a novel small-molecule microtubule inhibitor, MPT0B098, on STAT3 signaling in oral squamous cell carcinoma (OSCC). Treatment of various OSCC cells with MPT0B098 induced growth inhibition, cell cycle arrest and apoptosis, as well as increased the protein level of SOCS3. The accumulation of SOCS3 protein enhanced its binding to JAK2 and TYK2 which facilitated the ubiquitination and degradation of JAK2 and TYK2, resulting in a loss of STAT3 activity. The inhibition of STAT3 activity led to sensitization of OSCC cells to MPT0B098 cytotoxicity, indicating that STAT3 is a key mediator of drug resistance in oral carcinogenesis. Moreover, the combination of MPT0B098 with the clinical drug cisplatin or 5-FU significantly augmented growth inhibition and apoptosis in OSCC cells. Taken together, our results provide a novel mechanism for the action of MPT0B098 in which the JAK2/STAT3 signaling pathway is suppressed through the modulation of SOCS3 protein level. The findings also provide a promising combinational therapy of MPT0B098 for OSCC.

Vitamin C supports conversion of human γδ T cells into FOXP3-expressing regulatory cells by epigenetic regulation

Human γδ T cells are potent cytotoxic effector cells, produce a variety of cytokines, and can acquire regulatory activity. Induction of FOXP3, the key transcription factor of regulatory T cells (Treg), by TGF-β in human Vγ9 Vδ2 T cells has been previously reported. Vitamin C is an antioxidant and acts as multiplier of DNA hydroxymethylation. Here we have investigated the effect of the more stable phospho-modified Vitamin C (pVC) on TGF-β-induced FOXP3 expression and the resulting regulatory activity of highly purified human Vγ9 Vδ2 T cells. pVC significantly increased the TGF-β-induced FOXP3 expression and stability and also increased the suppressive activity of Vγ9 Vδ2 T cells. Importantly, pVC induced hypomethylation of the Treg-specific demethylated region (TSDR) in the FOXP3 gene. Genome-wide methylation analysis by Reduced Representation Bisulfite Sequencing additionally revealed differentially methylated regions in several important genes upon pVC treatment of γδ T cells. While Vitamin C also enhances effector functions of Vγ9 Vδ2 T cells in the absence of TGF-β, our results demonstrate that pVC potently increases the suppressive activity and FOXP3 expression in TGF-β-treated Vγ9 Vδ2 T cells by epigenetic modification of the FOXP3 gene.

Peptides with dual binding specificity for HLA-A2 and HLA-E are encoded by alternatively spliced isoforms of the antioxidant enzyme peroxiredoxin 5

Peptides with dual binding specificity for classical HLA class I and non-classical HLA-E molecules have been identified in virus-encoded proteins, but not in cellular proteins from normal or neoplastic cells. Expression screening of a melanoma cDNA library with a CTL clone recognizing an HLA-A2-restricted tumor-specific epitope encoded by mutant peroxiredoxin 5 (Prdx5), a stress-inducible peroxidase, led to the identification of two alternatively spliced isoforms of the same gene. These isoforms, which lack the catalytic cysteine fundamental for enzymatic activity, showed widespread expression in neoplastic and normal tissues but were unstable at the protein level, being detectable, following transient transfection, only after lactacystin treatment to inhibit proteasomal degradation. Isoform-specific sequences which formed, respectively, as result of exon 1 splicing to either exon 3 or 4, encoded two distinct nonapeptides (AMAPIKTHL and AMAPIKVRL, not present in the full-length protein) with anchor residues for HLA-A2 and HLA-E molecules and able to stabilize HLA-A2 and HLA-E cell surface expression. HLA-E+ targets, loaded with these peptides, were not recognized by NK cells expressing CD94/NKG2A inhibitory or CD94/NKG2C activatory receptors. However, both peptides were recognized, although with low avidity, by HLA-E-restricted CD8+ CTL. The nonapeptide AMAPIKVRL was used to elicit HLA-A2-restricted CTL clones that killed peptide-pulsed lymphoblastoid cell lines and melanoma cells expressing the corresponding Prdx5 isoform. Our results suggest that alternatively spliced isoforms of Prdx5, through the generation of HLA-E- and HLA-A2-restricted peptides may be part of immune-mediated stress response contributing to the detection and elimination of damaged normal or neoplastic cells.

The SUMO E3 ligase SIZ1 partially regulates STOP1 SUMOylation and stability in Arabidopsis thaliana

The zinc finger transcription factor STOP1 plays a crucial role in aluminum (Al) resistance and low phosphate (Pi) response. Al stress and low Pi availability do not affect STOP1 mRNA expression but are able to induce STOP1 protein accumulation by post-transcriptional regulatory mechanisms. We recently reported that STOP1 can be mono-SUMOylated at K40, K212, or K395 sites, and deSUMOylated by the SUMO protease ESD4. SUMOylation of STOP1 is important for the regulation of STOP1 protein function and Al resistance. In the present study, we further characterized the role of the SUMO E3 ligase SIZ1 in STOP1 SUMOylation, Al resistance and low Pi response. We found that mutation of SIZ1 reduced but not eliminated STOP1 SUMOylation, suggesting that SIZ1-dependent and -independent pathways are involved in the regulation of STOP1 SUMOylation. The STOP1 protein levels were decreased in siz1 mutants. Nevertheless, the expression of STOP1-target gene AtALMT1 was increased instead of reduced in siz1 mutants. The mutants showed enhanced Al resistance and low Pi response. Our results suggest that SIZ1 regulates Al resistance and low Pi response likely through the modulation of AtALMT1 expression.

The interaction between ionic liquids modified magnetic nanoparticles and bovine serum albumin and the cytotoxicity to HepG-2 cells

The interaction between ionic liquids modified magnetic Fe3O4 (Fe2) and bovine serum albumin (BSA) is reported and is compared with NH2 functionalized magnetic nanoparticles Fe3O4 (Fe1) based on the UV-visible spectrum, steady-state fluorescence measurements, synchronous fluorescence and DSC methods. The results indicate a static quenching mechanism operating in both nanoparticles. The binding constant of the Fe2-BSA complex calculated from fluorescence data shows that BSA has a low binding affinity for Fe2 than Fe1. DSC data reveal that the thermal stability process of BSA in the Fe2-BSA complex is semi-reversible. This demonstrates that the ionic liquid modified magnetic nanoparticles (Fe2) enhance the thermostability of BSA in the range of 20-40°C, and protein attached Fe2 has higher thermal stability than free BSA. Moreover, the in vitro assay results show that Fe2 shows low cytotoxicity to HepG-2 cells.

Hydration patterns of graphene-based nanomaterials (GBNMs) play a major role in the stability of a helical protein: a molecular dynamics simulation study

Graphene-based nanomaterials (GBNMs) [graphene oxide (GO), reduced graphene oxide (rGO), and graphene] have been recognized as potential candidates for various biomedical applications ranging from biosensing platform to cellular delivery of proteins and peptides. However, GBNMs induced conformational changes in proteins are the major concerns in realizing their full potential in aforementioned applications. Despite several studies, the effect of GBNMs on the conformation of proteins is still not well understood. Therefore, an attempt was made to investigate the effect of GBNMs on the adsorption and conformation of positively charged cytoplasmic protein using molecular dynamics (MD) simulations. Our study showed that the adsorption of protein on GO was highly selective and mediated through electrostatic interactions (hydrogen bond/salt bridge interactions), whereas the van der Waals and π-π stacking interactions were the major driving forces for the adsorption of protein on rGO and graphene. The secondary structure analysis showed the conformational stability of the protein on GO may be attributed to the extensive hydration of GO surface and the absence of tyrosine residues in π-π stacking with π regions of GO. The GO surface acts as a hydrogen bond acceptor similar to the protein's natural receptor present in a physiological environment. This computational study has also explored the artificial protein receptor like potential of GO.

The rust transferred proteins-a new family of effector proteins exhibiting protease inhibitor function

Only few fungal effectors have been described to be delivered into the host cell during obligate biotrophic interactions. RTP1p, from the rust fungi Uromyces fabae and U. striatus, was the first fungal protein for which localization within the host cytoplasm could be demonstrated directly. We investigated the occurrence of RTP1 homologues in rust fungi and examined the structural and biochemical characteristics of the corresponding gene products. The analysis of 28 homologues showed that members of the RTP family are most likely to occur ubiquitously in rust fungi and to be specific to the order Pucciniales. Sequence analyses indicated that the structure of the RTPp effectors is bipartite, consisting of a variable N-terminus and a conserved and structured C-terminus. The characterization of Uf-RTP1p mutants showed that four conserved cysteine residues sustain structural stability. Furthermore, the C-terminal domain exhibits similarities to that of cysteine protease inhibitors, and it was shown that Uf-RTP1p and Us-RTP1p are able to inhibit proteolytic activity in Pichia pastoris culture supernatants. We conclude that the RTP1p homologues constitute a rust fungi-specific family of modular effector proteins comprising an unstructured N-terminal domain and a structured C-terminal domain, which exhibit protease inhibitory activity possibly associated with effector function during biotrophic interactions.

Denaturation-resistant bifunctional colloidal superstructures assembled via the proteinaceous barnase-barstar interface

To date, a number of biomolecule-mediated nanoparticle self-assembly systems have been developed that are amenable to controllable disassembly under relatively gentle conditions. However, for some applications such as design of self-assembled multifunctional theragnostic agents, high stability of the assembled structures can be of primary importance. Here, we report extraordinarily high durability of protein-assisted nanoparticle self-assembly systems yielding bifunctional colloidal superstructures resistant to extreme denaturing conditions intolerable for most proteins (e.g., high concentrations of chaotropic agents, high temperature). Among the tested systems (barnase-barstar (BBS), streptavidin-biotin, antibody-antigen, and protein A-immunoglobulin), the BBS is notable due to the combination of its high resistance to severe chemical perturbation and unique advantages offered by genetic engineering of this entirely protein-based system. Comparison of the self-assembly systems shows that whereas in all cases the preassembled structures proved essentially resistant to extreme conditions, the ability of the complementary biomolecular pairs to mediate assembly of the initial biomolecule-particle conjugates differs substantially in these conditions.

Synergistic activity of BET inhibitor MK-8628 and PLK inhibitor Volasertib in preclinical models of medulloblastoma

Medulloblastoma is the most prevalent central nervous system tumor in children. Targeted treatment approaches for patients with high-risk medulloblastoma are needed as current treatment regimens are not curative in many cases and cause significant therapy-related morbidity. Medulloblastoma harboring MYC amplification have the most aggressive clinical course and worst outcome. Targeting the BET protein BRD4 has significant anti-tumor effects in preclinical models of MYC-amplified medulloblastoma, however, in most cases these are not curative. We here assessed the therapeutic efficacy of the orally bioavailable BRD4 inhibitor, MK-8628, in preclinical models of medulloblastoma. MK-8628 showed therapeutic efficacy against in vitro and in vivo models of MYC-amplified medulloblastoma by inducing apoptotic cell death and cell cycle arrest. Gene expression analysis of cells treated with MK-8628 showed that anti-tumor effects were accompanied by significant repression of MYC transcription as well as disruption of MYC-regulated transcriptional programs. Additionally, we found that targeting of MYC protein stability through pharmacological PLK1 inhibition showed synergistic anti-medulloblastoma effects when combined with MK-8628 treatment. Thus, MK-8628 is effective against preclinical high-risk medulloblastoma models and its effects can be enhanced through simultaneous targeting of PLK1.

Post-translational modification of the interferon-gamma receptor alters its stability and signaling

The IFN gamma receptor 1 (IFNGR1) binds IFN-γ and activates gene transcription pathways crucial for controlling bacterial and viral infections. Although decreases in IFNGR1 surface levels have been demonstrated to inhibit IFN-γ signaling, little is known regarding the molecular mechanisms controlling receptor stability. Here, we show in epithelial and monocytic cell lines that IFNGR1 displays K48 polyubiquitination, is proteasomally degraded, and harbors three ubiquitin acceptor sites at K277, K279, and K285. Inhibition of glycogen synthase kinase 3 beta (GSK3β) destabilized IFNGR1 while overexpression of GSK3β increased receptor stability. We identified critical serine and threonine residues juxtaposed to ubiquitin acceptor sites that impacted IFNGR1 stability. In CRISPR-Cas9 IFNGR1 generated knockout cell lines, cellular expression of IFNGR1 plasmids encoding ubiquitin acceptor site mutations demonstrated significantly impaired STAT1 phosphorylation and decreased STAT1-dependent gene induction. Thus, IFNGR1 undergoes rapid site-specific polyubiquitination, a process modulated by GSK3β. Ubiquitination appears to be necessary for efficient IFNGR1-dependent gamma gene induction and represents a relatively uncharacterized regulatory mechanism for this receptor.