Microbial Interaction between Lactiplantibacillus plantarum and Saccharomyces cerevisiae: Transcriptome Level Mechanism of Cell-Cell Antagonism.

Lactiplantibacillus plantarum and Saccharomyces cerevisiae are frequently co-isolated in food, although playing different roles. This study aimed at investigating the microbial interaction between L. plantarum and S. cerevisiae, especially cell-cell direct interaction and their mechanism. Cell-cell and supernatant-cell coculture models were set up, with CFU counting, OD600 measurement, optical and atomic force microscopy performed to examine the growth and morphology of L. plantarum and S. cerevisiae cells. In cell-cell coculture model, L. plantarum cells inhibited S. cerevisiae growth (inhibition rate ~80%) with its own growth pattern unaffected. Cell-cell aggregation happened during coculture with surface roughness changed and partial S. cerevisiae cell lysis. Mature (24 h) L. plantarum cell-free culture supernatant showed inhibition (35%-75%) on S. cerevisiae growth independent of pH level, while supernatant from L. plantarum-S. cerevisiae coculture showed relatively stronger inhibition. Upon transcriptomics analysis, hypothesis on the mechanism of microbial interaction between L. plantarum and S. cerevisiae was demonstrated. When L. plantarum cell density reached threshold at 24 h, all genes in lamBDCA quorum sensing (QS) system was upregulated to potentially increase adhesion capability, leading to the aggregation to S. cerevisiae cell. The downregulation of whole basic physiological activity from DNA to RNA to protein, cell cycle, meiosis, and mitogen-activated protein kinase (MAPK) signaling pathways, as well as growth maintenance essential genes ari1, skg6, and kex2/gas1 might induce the decreased growth and proliferation rate and partial death of S. cerevisiae cells in coculture. IMPORTANCE L. plantarum and S. cerevisiae are frequently co-isolated in food, although playing different roles. The co-existence of L. plantarum and S. cerevisiae could result in variable effects, raising economic benefits and safety concerns in food industry. Previous research has reported the microbial interaction between L. plantarum and S. cerevisiae mainly rely on the signaling through extracellular metabolites. However, cell-cell aggregation has been observed with mechanism remain unknown. In the current study, the microbial interaction between L. plantarum and S. cerevisiae was investigated with emphasis on cell-cell direct interaction and further in-depth transcriptome level study showed the key role of lamBDCA quorum sensing system in L. plantarum. The results yield from this study demonstrated the antagonistic effect between L. plantarum and S. cerevisiae.

Bulleyaconitine A is a sensitive substrate and competitive inhibitor of CYP3A4: One of the possible explanations for clinical adverse reactions.

Bulleyaconitine A (BLA), a toxic Aconitum alkaloid, is a potent analgesic that is clinically applied to treat rheumatoid arthritis, osteoarthritis and lumbosacral pain. BLA-related adverse reactions occur frequently, but whether the underlying mechanism is related to its metabolic interplay with drug-metabolizing enzymes remains unclear. This study aimed to elucidate the metabolic characteristics of BLA and its affinity action and mechanism to drug-metabolizing enzymes to reveal whether BLA-related adverse reactions are modulated by enzymes. After incubation with human liver microsomes and recombinant human cytochrome P450 enzymes, we found that BLA was predominantly metabolized by CYP3A, in which CYP3A4 had an almost absolute advantage. In vitro, the CYP3A4 inhibitor ketoconazole noticeably suppressed the metabolism of BLA. In vivo, the AUC0-∞ values, cardiotoxicity and neurotoxicity of BLA in Cyp3a-inhibited mice were all obviously enhanced (P < 0.05) compared to those in normal mice. In the enzyme kinetics study, BLA was found to be a sensitive substrate of CYP3A4, and its characteristics were consistent with substrate inhibition (Km = 39.36 ± 10.47 µmol/L, Ks = 83.42 ± 19.65 µmol/L). BLA was further identified to be a competitive inhibitor of CYP3A4 with Ki = 53.64 µmol/L, since the intrinsic clearance (CLint) of midazolam, a selective CYP3A4 substrate, decreased significantly (P < 0.05) when incubated with BLA together in mouse liver microsomes. Overall, BLA is a sensitive substrate and competitive inhibitor of CYP3A4, and clinical adverse reactions of BLA may mechanistically related to the CYP3A4-mediated drug-drug interactions.

Mutations in the Hsp90 N Domain Identify a Site that Controls Dimer Opening and Expand Human Hsp90α Function in Yeast.

Hsp90 is a highly conserved molecular chaperone important for the activity of many client proteins. Hsp90 has an N-terminal ATPase domain (N), a middle domain (M) that interacts with clients and a C-terminal dimerization domain (C). "Closing" of dimers around clients is regulated by ATP binding, co-chaperones, and post-translational modifications. ATP hydrolysis coincides with release of mature client and resetting the reaction cycle. Humans have two Hsp90s: hHsp90α and hHsp90ß. Although 85% identical, hHsp90ß supports Hsp90 function in yeast much better than hHsp90α. Determining the basis of this difference would provide important insight into functional specificity of seemingly redundant Hsp90s, and the evolution of eukaryotic Hsp90 systems and clientele. Here, we found host co-chaperones Sba1, Cpr6 and Cpr7 inhibited hHsp90α function in yeast, and we identified mutations clustering in the N domain that considerably improved hHsp90α function in yeast. The strongest of these rescuer mutations accelerated nucleotide-dependent lid closing, N-M domain docking, and ATPase. It also disrupted binding to Sba1, which prolongs the closed state, and promoted N-M undocking and lid opening. Our data suggest the rescuer mutations improve function of hHsp90α in yeast by accelerating return to the open state. Our findings imply hHsp90α occupies the closed state too long to function effectively in yeast, and define an evolutionarily conserved region of the N domain involved in resetting the Hsp90 reaction cycle.

Mannoproteins from Saccharomyces cerevisiae stimulate angiogenesis by promoting the akt-eNOS signaling pathway in endothelial cells.

Mannoproteins (MPs) are a major component of yeast cell walls and consist of high levels of mannose in covalent complexes with proteins. MPs complexly enhance the immune system. We previously isolated a mutant yeast, K48L3, with a higher yield of MP from its cell wall than wild-type Saccharomyces cerevisiae, YPH499. We determined that K48L3 induces the release of nitric oxide in macrophage cells. The present study reports nitric-oxide-mediated angiogenesis by MP from K48L3 and the induction of the Akt/eNOS signal pathway. Western blotting and RT-PCR were used to demonstrate that MP treatment resulted in the upregulation of p-Akt, p-eNOS, and angiogenesis-mediated gene expression. Moreover, the angiogenesis activity of the MPs was demonstrated using three angiogenesis assays, namely, a cell migration assay, a tube-forming assay, and an ex vivo aorta ring assay. Thus, this study demonstrates for the first time that MPs from S. cerevisiae K48L3 induce angiogenesis in HUVECs via the Akt-eNOS-dependent signaling pathway.

Tsr4 and Nap1, two novel members of the ribosomal protein chaperOME.

Dedicated chaperones protect newly synthesized ribosomal proteins (r-proteins) from aggregation and accompany them on their way to assembly into nascent ribosomes. Currently, only nine of the ∼80 eukaryotic r-proteins are known to be guarded by such chaperones. In search of new dedicated r-protein chaperones, we performed a tandem-affinity purification based screen and looked for factors co-enriched with individual small subunit r-proteins. We report the identification of Nap1 and Tsr4 as direct binding partners of Rps6 and Rps2, respectively. Both factors promote the solubility of their r-protein clients in vitro. While Tsr4 is specific for Rps2, Nap1 has several interaction partners including Rps6 and two other r-proteins. Tsr4 binds co-translationally to the essential, eukaryote-specific N-terminal extension of Rps2, whereas Nap1 interacts with a large, mostly eukaryote-specific binding surface of Rps6. Mutation of the essential Tsr4 and deletion of the non-essential Nap1 both enhance the 40S synthesis defects of the corresponding r-protein mutants. Our findings highlight that the acquisition of eukaryote-specific domains in r-proteins was accompanied by the co-evolution of proteins specialized to protect these domains and emphasize the critical role of r-protein chaperones for the synthesis of eukaryotic ribosomes.

Target of rapamycin complex 1 and Tap42-associated phosphatases are required for sensing changes in nitrogen conditions in the yeast Saccharomyces cerevisiae.

In yeast target of rapamycin complex 1 (TORC1) and Tap42-associated phosphatases regulate expression of genes involved in nitrogen limitation response and the nitrogen discrimination pathway. However, it remains unclear whether TORC1 and the phosphatases are required for sensing nitrogen conditions. Utilizing temperature sensitive mutants of tor2 and tap42, we examined the role of TORC1 and Tap42 in nuclear entry of Gln3, a key transcription factor in yeast nitrogen metabolism, in response to changes in nitrogen conditions. Our data show that TORC1 is essential for Gln3 nuclear entry upon nitrogen limitation and downshift in nitrogen quality. However, Tap42-associated phosphatases are required only under nitrogen limitation condition. In cells grown in poor nitrogen medium, the nitrogen permease reactivator kinase (Npr1) inhibits TORC1 activity and alters its association with Tap42, rendering Tap42-associated phosphatases unresponsive to nitrogen limitation. These findings demonstrate a direct role for TORC1 and Tap42-associated phosphatases in sensing nitrogen conditions and unveil an Npr1-dependent mechanism that controls TORC1 and the phosphatases in response to changes in nitrogen quality.

FANCJ helicase controls the balance between short- and long-tract gene conversions between sister chromatids.

The FANCJ DNA helicase is linked to hereditary breast and ovarian cancers as well as bone marrow failure disorder Fanconi anemia (FA). Although FANCJ has been implicated in the repair of DNA double-strand breaks (DSBs) by homologous recombination (HR), the molecular mechanism underlying the tumor suppressor functions of FANCJ remains obscure. Here, we demonstrate that FANCJ deficient human and hamster cells exhibit reduction in the overall gene conversions in response to a site-specific chromosomal DSB induced by I-SceI endonuclease. Strikingly, the gene conversion events were biased in favour of long-tract gene conversions in FANCJ depleted cells. The fine regulation of short- (STGC) and long-tract gene conversions (LTGC) by FANCJ was dependent on its interaction with BRCA1 tumor suppressor. Notably, helicase activity of FANCJ was essential for controlling the overall HR and in terminating the extended repair synthesis during sister chromatid recombination (SCR). Moreover, cells expressing FANCJ pathological mutants exhibited defective SCR with an increased frequency of LTGC. These data unravel the novel function of FANCJ helicase in regulating SCR and SCR associated gene amplification/duplications and imply that these functions of FANCJ are crucial for the genome maintenance and tumor suppression.

Kv3.1/Kv3.2 channel positive modulators enable faster activating kinetics and increase firing frequency in fast-spiking GABAergic interneurons.

Due to their fast kinetic properties, Kv3.1 voltage gated potassium channels are important in setting and controlling firing frequency in neurons and pivotal in generating high frequency firing of interneurons. Pharmacological activation of Kv3.1 channels may possess therapeutic potential for treatment of epilepsy, hearing disorders, schizophrenia and cognitive impairments. Here we thoroughly investigate the selectivity and positive modulation of the two small molecules, EX15 and RE01, on Kv3 channels. Selectivity studies, conducted in Xenopus laevis oocytes confirmed a positive modulatory effect of the two compounds on Kv3.1 and to a minor extent on Kv3.2 channels. RE01 had no effect on the Kv3.3 and Kv3.4 channels, whereas EX15 had an inhibitory impact on the Kv3.4 mediated current. Voltage-clamp experiments in monoclonal hKv3.1b/HEK293 cells (34 °C) revealed that the two compounds indeed induced larger currents and faster activation kinetics. They also decrease the speed of deactivation and shifted the voltage dependence of activation, to a more negative activation threshold. Application of action potential clamping and repetitive stimulation protocols of hKv3.1b expressing HEK293 cells revealed that EX15 and RE01 significantly increased peak amplitude, half width and decay time of Kv3.1 mediated currents, even during high-frequency action potential clamping (250 Hz). In rat hippocampal slices, EX15 and RE01 increased neuronal excitability in fast-spiking interneurons in dentate gyrus. Action potential frequency was prominently increased at minor depolarizing steps, whereas more marginal effects of EX15 and RE01 were observed after stronger depolarizations. In conclusion, our results suggest that EX15 and RE01 positive modulation of Kv3.1 and Kv3.2 currents facilitate increased firing frequency in fast-spiking GABAergic interneurons.

Evaluation of In Vitro Function by Subcellular Distribution of Lysosomal and Peroxisomal Protein in Saccharomyces cerevisiae.

Lysosomes and peroxisomes, contained in all eukaryote cells, are similar but have completely different function. Lysosomes have three dozen different kinds of hydrolytic enzymes and release lysosomal enzymes to digest intra/extracellular materials. The lysosomal enzymes degrade bacteria cell walls and proteins in cell, exhibiting an antimicrobial and anticancerous effect. Peroxisomes contain oxidative enzymes such as peroxidase, D-amino acid oxidase, and catalase allowing the ability to degrade melanin in hyperpigmentation disorders. Exposure of Saccharomyces cerevisiae and HeLa cells to chemical stress alters lysosomal and peroxisomal enzymes. Chemical stresses such as phenylhydrazine, sodium azide, rolipram, NH4Cl, salicylic acid, H2O2 and 6-hydroxdopamine (6-OHDA) have been suggested to stimulate In Vitro function of lysosome and peroxisome-like organelles (LPO) isolated from S. cerevisiae, and we demonstrate activity of LPO in HeLa cells through chemical analysis. The lysosomes of cells exposed to salicylic acid, 6-OHDA and H2O2 had increased antimicrobial and anticancerous activity, and the peroxisomes of cells exposed to phenylhydrazine and sodium azide had reduced effect of melanin degradation. Therefore, our results suggest that activity of lysosomes and peroxisomes can be regulated by several stimuli, therefore lysosomes may be used as antimicrobial agents, apoptosis-inducing materials, or peroxisomal enzymes to be useful agents for cosmeceutical skin lightening and treatment of hyperpigmentation disorders.

Recombinant L-asparaginase 1 from Saccharomyces cerevisiae: an allosteric enzyme with antineoplastic activity.

L-asparaginase (L-ASNase) (EC 3.5.1.1) is an important enzyme for the treatment of acute lymphoblastic leukaemia. Currently, the enzyme is obtained from bacteria, Escherichia coli and Erwinia chrysanthemi. The bacterial enzymes family is subdivided in type I and type II; nevertheless, only type II have been employed in therapeutic proceedings. However, bacterial enzymes are susceptible to induce immune responses, leading to a high incidence of adverse effects compromising the effectiveness of the treatment. Therefore, alternative sources of L-ASNase may be useful to reduce toxicity and enhance efficacy. The yeast Saccharomyces cerevisiae has the ASP1 gene responsible for encoding L-asparaginase 1 (ScASNase1), an enzyme predicted as type II, like bacterial therapeutic isoforms, but it has been poorly studied. Here we characterised ScASNase1 using a recombinant enzyme purified by affinity chromatography. ScASNase1 has specific activity of 196.2 U/mg and allosteric behaviour, like type I enzymes, but with a low K0.5 = 75 µM like therapeutic type II. We showed through site-directed mutagenesis that the T64-Y78-T141-K215 residues are involved in catalysis. Furthermore, ScASNase1 showed cytotoxicity for the MOLT-4 leukemic cell lineage. Our data show that ScASNase1 has characteristics described for the two subfamilies of l-asparaginase, types I and II, and may have promising antineoplastic properties.

A pyruvate decarboxylase-mediated therapeutic strategy for mimicking yeast metabolism in cancer cells.

Cancer cells have high rates of glycolysis and lactic acid fermentation in order to fuel accelerated rates of cell division (Warburg effect). Here, we present a strategy for merging cancer and yeast metabolism to remove pyruvate, a key intermediate of cancer cell metabolism, and produce the toxic compound acetaldehyde. This approach was achieved by administering the yeast enzyme pyruvate decarboxylase to triple negative breast cancer cells. To overcome the challenges of protein delivery, a nanoparticle-based system consisting of cationic lipids and porous silicon were employed to obtain efficient intracellular uptake. The results demonstrate that the enzyme therapy decreases cancer cell viability through production of acetaldehyde and reduction of lactic acid fermentation.

Targeted antitumor prodrug therapy using CNGRC-yCD fusion protein in combination with 5-fluorocytosine.

BACKGROUND: The enzyme-prodrug system is considered a promising tool for tumor treatment when conjugated with a targeting molecule. The asparagine-glycine-arginine (NGR) motif is a developing and interesting targeting peptide that could specifically bind to aminopeptidase N (APN), which is an NGR receptor expressed on the cell membrane of angiogenic endothelial cells and a number of tumor cells within the tumor tissues. The objective of this study was to develop a novel targeted enzyme-prodrug system using 5-fluorocytosine (5-FC) and an NGR-containing peptide fused with yeast cytosine deaminase (yCD), i.e. CNGRC-yCD fusion protein, to target APN-expressing cells within the tumor tissues and to convert 5-FC into 5-fluorouracil (5-FU) to kill tumors. RESULTS: Both yCD and CNGRC-yCD proteins were cloned into the pET28a vector and expressed by an Escherichia coli host. Both yCD and CNGRC-yCD proteins were purified and the yields were approximately 20 mg/L with over 95 % purity. The binding assay demonstrated that the CNGRC-yCD fusion protein had specific binding affinity toward purified APN recombinant protein and high-APN-expressing cells, including human endothelial cells (HUVECs) and various types of human tumor cell lines, but not low-APN-expressing tumor cell lines. Moreover, the enzyme activity and cell viability assay showed that the CNGRC-yCD fusion protein could effectively convert 5-FC into 5-FU and resulted in significant cell death in both high-APN-expressing tumor cells and HUVECs. CONCLUSIONS: This study successfully constructs a new targeting enzyme-prodrug system, CNGRC-yCD fusion protein/5-FC. Systematic experiments demonstrated that the CNGRC-yCD protein retained both the APN-binding affinity of NGR and the enzyme activity of yCD to convert 5-FC into 5-FU. The combined treatment of the CNGRC-yCD protein with 5-FC resulted in the significantly increased cell death of high-APN-expressing cells as compared to that of low-APN-expressing cells.

Saccharomyces cerevisiae asparaginase II, a potential antileukemic drug: Purification and characterization of the enzyme expressed in Pichia pastoris.

Asparaginase obtained from Escherichia coli and Erwinia chrysanthemi are used to treat acute lymphocytic leukaemia and non-Hodgkin's lymphoma. However, these agents cause severe adverse effects. Saccharomyces cerevisiae asparaginase II, encoded by the ASP3 gene, could be a potential candidate for the formulation of new drugs. This work aimed to purify and characterize the periplasmic asparaginase produced by a recombinant Pichia pastoris strain harbouring the ASP3 gene. The enzyme was purified to homogeneity with an activity recovery of 51.3%. The estimated molecular mass of the enzyme was 136 kDa (under native conditions) and 48.6 kDa and 44.6 kDa (under reducing conditions), suggesting an oligomeric structure. The recombinant asparaginase is apparently non-phosphorylated, and the major difference between the monomers seems to be their degree of glycosylation. The enzyme showed an isoelectric point of 4.5 and maximum activity at 46 °C and pH 7.2, retaining 92% of the activity at 37 °C. Circular dichroism and fluorescence analyses showed that the enzyme structure is predominantly α-helical with the contribution of ß-sheet and that it remains stable up to 45 °C and in the pH range of 6-10. In vitro tests indicated that the recombinant asparaginase demonstrated antitumoural activity against K562 leukaemic cells.

Disparate Mutations Confer Therapeutic Gain of Hsp104 Function.

Hsp104, a protein disaggregase from yeast, can be engineered and potentiated to counter TDP-43, FUS, or α-synuclein misfolding and toxicity implicated in neurodegenerative disease. Here, we reveal that extraordinarily disparate mutations potentiate Hsp104. Remarkably, diverse single missense mutations at 20 different positions interspersed throughout the middle domain (MD) and small domain of nucleotide-binding domain 1 (NBD1) confer a therapeutic gain of Hsp104 function. Moreover, potentiation emerges from deletion of MD helix 3 or 4 or via synergistic missense mutations in the MD distal loop and helix 4. We define the most critical aspect of Hsp104 potentiation as enhanced disaggregase activity in the absence of Hsp70 and Hsp40. We suggest that potentiation likely stems from a loss of a fragilely constrained autoinhibited state that enables precise spatiotemporal regulation of disaggregase activity.

Repurposing Hsp104 to Antagonize Seminal Amyloid and Counter HIV Infection.

Naturally occurring proteolytic fragments of prostatic acid phosphatase (PAP248-286 and PAP85-120) and semenogelins (SEM1 and SEM2) form amyloid fibrils in seminal fluid, which capture HIV virions and promote infection. For example, PAP248-286 fibrils, termed SEVI (semen-derived enhancer of viral infection), can potentiate HIV infection by several orders of magnitude. Here, we design three disruptive technologies to rapidly antagonize seminal amyloid by repurposing Hsp104, an amyloid-remodeling nanomachine from yeast. First, Hsp104 and an enhanced engineered variant, Hsp104(A503V), directly remodel SEVI and PAP85-120 fibrils into non-amyloid forms. Second, we elucidate catalytically inactive Hsp104 scaffolds that do not remodel amyloid structure, but cluster SEVI, PAP85-120, and SEM1(45-107) fibrils into larger assemblies. Third, we modify Hsp104 to interact with the chambered protease ClpP, which enables coupled remodeling and degradation to irreversibly clear SEVI and PAP85-120 fibrils. Each strategy diminished the ability of seminal amyloid to promote HIV infection, and could have therapeutic utility.

The Central Role of Proprotein Convertase Subtilisin/Kexin Type 9 in Septic Pathogen Lipid Transport and Clearance.

Microbial cell walls contain pathogenic lipids, including LPS in gram-negative bacteria, lipoteichoic acid in gram-positive bacteria, and phospholipomannan in fungi. These pathogen lipids are major ligands for innate immune receptors and figure prominently in triggering the septic inflammatory response. Alternatively, pathogen lipids can be cleared and inactivated, thus limiting the inflammatory response. Accordingly, biological mechanisms for sequestering and clearing pathogen lipids from the circulation have evolved. Pathogen lipids released into the circulation are initially bound by transfer proteins, notably LPS binding protein and phospholipid transfer protein, and incorporated into high-density lipoprotein particles. Next, LPS binding protein, phospholipid transfer protein, and other transfer proteins transfer these lipids to ApoB-containing lipoproteins, including low-density (LDL) and very-low-density lipoproteins and chylomicrons. Pathogen lipids within these lipoproteins and their remnants are then cleared from the circulation by the liver. Hepatic clearance involves the LDL receptor (LDLR) and possibly other receptors. Once absorbed by the liver, these lipids are then excreted in the bile. Recent evidence suggests pathogen lipid clearance can be modulated. Importantly, reduced proprotein convertase subtilisin/kexin type 9 activity increases recycling of the LDLR and thereby increases LDLR on the surface of hepatocytes, which increases clearance by the liver of pathogen lipids transported in LDL. Increased pathogen lipid clearance, which can be achieved by inhibiting proprotein convertase subtilisin/kexin type 9, may decrease the systemic inflammatory response to sepsis and improve clinical outcomes.

Remodeling Amyloid Fibers: Baker's Yeast Shows Us the Way.

Proteopathies are a large and diverse group of human diseases that are caused by protein misfolding. Well-known examples of proteopathies are Alzheimer's and Parkinson's disease, which are both linked to amyloid fibril formation. In this issue of Chemistry & Biology, Castellano et al. (2015) describe the way to harness the power of a protein from baker's yeast, Hsp104, to disaggregate the fibrils.

Selenoglycoproteins attenuate adhesion of tumor cells to the brain microvascular endothelium via a process involving NF-κB activation.

Selenium-containing compounds and selenized yeast have anticancer properties. In order to address possible mechanisms involved in these effects, selenoglycoproteins (SGPs) were extracted from selenium-enriched yeast at pH 4.0 and 6.5 (the fractions are called SGP40 and SGP65, respectively), followed by evaluation of their impact on the interactions of lung and breast tumor cells with human brain microvascular endothelial cells (HBMECs). Extracted SGPs, especially SGP40, significantly inhibited adhesion of tumor cells to HBMECs and their transendothelial migration. Because the active components of SGPs are unknown, small selenium-containing compounds [leucyl-valyl-selenomethionyl-arginine (LVSe-MR) and methylselenoadenosine (M-Se-A)], which are normally present in selenized yeast, were introduced as additional treatment groups. Treatment of HBMECs with SGP40, LVSe-MR and M-Se-A induced changes in gene signatures, which suggested a central involvement of nuclear factor (NF)-κB-dependent pathway. These observations were confirmed in the subsequent analysis of NF-κB DNA binding activity, quantitative measurements of the expression of selected genes and proteins, and tumor cell adhesion assay with a specific NF-κB inhibitor as the additional treatment factor. These findings indicate that specific organic selenium-containing compounds have the ability to inhibit tumor cell adhesion to brain endothelial cells via down-regulation of NF-κB. SGPs appear to be more effective than small selenium-containing compounds, suggesting the role of not only selenium but also the glycoprotein component in the observed protective impact.

Reporter-based growth assay for systematic analysis of protein degradation.

Protein degradation by the ubiquitin-proteasome system (UPS) is a major regulatory mechanism for protein homeostasis in all eukaryotes. The standard approach to determining intracellular protein degradation relies on biochemical assays for following the kinetics of protein decline. Such methods are often laborious and time consuming and therefore not amenable to experiments aimed at assessing multiple substrates and degradation conditions. As an alternative, cell growth-based assays have been developed, that are, in their conventional format, end-point assays that cannot quantitatively determine relative changes in protein levels. Here we describe a method that faithfully determines changes in protein degradation rates by coupling them to yeast cell-growth kinetics. The method is based on an established selection system where uracil auxotrophy of URA3-deleted yeast cells is rescued by an exogenously expressed reporter protein, comprised of a fusion between the essential URA3 gene and a degradation determinant (degron). The reporter protein is designed so that its synthesis rate is constant whilst its degradation rate is determined by the degron. As cell growth in uracil-deficient medium is proportional to the relative levels of Ura3, growth kinetics are entirely dependent on the reporter protein degradation. This method accurately measures changes in intracellular protein degradation kinetics. It was applied to: (a) Assessing the relative contribution of known ubiquitin-conjugating factors to proteolysis (b) E2 conjugating enzyme structure-function analyses (c) Identification and characterization of novel degrons. Application of the degron-URA3-based system transcends the protein degradation field, as it can also be adapted to monitoring changes of protein levels associated with functions of other cellular pathways.

Preserving catalytic activity and enhancing biochemical stability of the therapeutic enzyme asparaginase by biocompatible multilayered polyelectrolyte microcapsules.

The present study focuses on the formation of microcapsules containing catalytically active L-asparaginase (L-ASNase), a protein drug of high value in antileukemic therapy. We make use of the layer-by-layer (LbL) technique to coat protein-loaded calcium carbonate (CaCO3) particles with two or three poly dextran/poly-L-arginine-based bilayers. To achieve high loading efficiency, the CaCO3 template was generated by coprecipitation with the enzyme. After assembly of the polymer shell, the CaCO3 core material was dissolved under mild conditions by dialysis against 20 mM EDTA. Biochemical stability of the encapsulated L-asparaginase was analyzed by treating the capsules with the proteases trypsin and thrombin, which are known to degrade and inactivate the enzyme during leukemia treatment, allowing us to test for resistance against proteolysis by physiologically relevant proteases through measurement of residual l-asparaginase activities. In addition, the thermal stability, the stability at the physiological temperature, and the long-term storage stability of the encapsulated enzyme were investigated. We show that encapsulation of l-asparaginase remarkably improves both proteolytic resistance and thermal inactivation at 37 °C, which could considerably prolong the enzyme's in vivo half-life during application in acute lymphoblastic leukemia (ALL). Importantly, the use of low EDTA concentrations for the dissolution of CaCO3 by dialysis could be a general approach in cases where the activity of sensitive biomacromolecules is inhibited, or even irreversibly damaged, when standard protocols for fabrication of such LbL microcapsules are used. Encapsulated and free enzyme showed similar efficacies in driving leukemic cells to apoptosis.