Protective Effects of Compounds from Cimicifuga dahurica against Amyloid Beta Production in Vitro and Scopolamine-Induced Memory Impairment in Vivo.

Cimicifuga dahurica has traditionally been used as an antipyretic, analgesic, and anti-inflammatory agent and as a treatment for uterine and anal prolapse. This study has investigated the potential beneficial effects of this medicinal plant and its components on Alzheimer's disease (AD) with a focus on amyloid beta (Aß) production and scopolamine-induced memory impairment in mice. An ethanol extract from C. dahurica roots decreased Aß production in APP-CHO cells [Chinese hamster ovarian (CHO) cells stably expressing amyloid precursor protein (APP)], as determined by an enzyme-linked immunosorbent assay and Western blot analysis. Then, the compounds isolated from C. dahurica were tested for their antiamyloidogenic activities. Four compounds (1-4) efficiently interrupted Aß generation by suppressing the level of ß-secretase in APP-CHO cells. Moreover, the in vivo experimental results demonstrated that compound 4 improved the cognitive performances of mice with scopolamine-induced disruption on behavioral tests and the expression of memory-related proteins. Taken together, these results suggest that C. dahurica and its constituents are potential agents for preventing or alleviating the symptoms of AD.

Envelope-deforming antiviral peptide derived from influenza virus M2 protein.

Molecules interfering with lipid bilayer function exhibit strong antiviral activity against a broad range of enveloped viruses, with a lower risk of resistance development than that for viral protein-targeting drugs. Amphipathic peptides are rich sources of such membrane-interacting antivirals. Here, we report that influenza viruses were effectively inactivated by M2 AH, an amphipathic peptide derived from the M2 protein of the influenza virus. Although overall hydrophobicity () of M2 AH was not related to antiviral activity, modification of the hydrophobic moment (<µH>) of M2 AH dramatically altered the antiviral activity of this peptide. M2 MH, a derivative of M2 AH with a <µH> of 0.874, showed a half maximal inhibitory concentration (IC50) of 53.3 nM against the A/PR/8/34 strain (H1N1), which is 16-times lower than that of M2 AH. The selectivity index (IC50/CC50), where CC50 is the half maximal cytotoxic concentration, was 360 for M2 MH and 81 for M2 AH. Dynamic light scattering spectroscopy and electron microscopy revealed that M2 AH-derived peptides did not disrupt liposomes but altered the shape of viruses. This result suggests that the shape of virus envelope was closely related to its activity. Thus, we propose that deforming without rupturing the membranes may achieve a high selectivity index for peptide antivirals.

Anti-Amyloidogenic Effects of Asarone Derivatives From Perilla frutescens Leaves against Beta-Amyloid Aggregation and Nitric Oxide Production.

Alzheimer's disease (AD) is a progressive, neurodegenerative brain disorder associated with loss of memory and cognitive function. Beta-amyloid (Aß) aggregates, in particular, are known to be highly neurotoxic and lead to neurodegeneration. Therefore, blockade or reduction of Aß aggregation is a promising therapeutic approach in AD. We have previously reported an inhibitory effect of the methanol extract of Perilla frutescens (L.) Britton (Lamiaceae) and its hexane fraction on Aß aggregation. Here, the hexane fraction of P. frutescens was subjected to diverse column chromatography based on activity-guided isolation methodology. This approach identified five asarone derivatives including 2,3-dimethoxy-5-(1E)-1-propen-1-yl-phenol (1), ß-asarone (2), 3-(2,4,5-trimethoxyphenyl)-(2E)-2-propen-1-ol (3), asaronealdehyde (4), and α-asarone (5). All five asarone derivatives efficiently reduced the aggregation of Aß and disaggregated preformed Aß aggregates in a dose-dependent manner as determined by a Thioflavin T (ThT) fluorescence assay. Furthermore, asarone derivatives protected PC12 cells from Aß aggregate-induced toxicity by reducing the aggregation of Aß, and significantly reduced NO production from LPS-stimulated BV2 microglial cells. Taken together, these results suggest that asarone derivatives derived from P. frutescens are neuroprotective and have the prophylactic and therapeutic potential in AD.

Constituents from Scutellaria barbata Inhibiting Nitric Oxide Production in LPS-Stimulated Microglial Cells.

The arial parts of Scutellaria barbata D. Don (Lamiaceae) efficiently inhibited NO production in BV2 microglial cells, and the active constituents were further isolated based on activity-guided isolation using silica-gel column chromatography, RP-C18 MPLC and prep-HPLC. As the results, 2 flavonoids including 6-methoxynaringenin (1) and 6-O-methylscutellarein (5), and 6 neo-clerodane diterpenes such as scutebarbatine W (2), scutebatas B (3), scutebarbatine B (4), scutebarbatine A (6), 6-O-nicotinolylscutebarbatine G (7), and scutebarbatine X (8) were isolated. The structures of these compounds were elucidated based on NMR and MS data, and the comparison of literature values. All the compounds except compound 7 inhibited NO production efficiently with IC50 values of lower than 50 µm. Particularly, compounds 1 and 8 were the most efficient with IC50 values of 25.8 and 27.4 µm, respectively. This is the first report suggesting the potential of S. barbata on the reduction of neuroinflammation.

Heterologous Expression of Der Homologs in an Escherichia coli der Mutant and Their Functional Complementation.

UNLABELLED: The unique Escherichia coli GTPase Der (double Era-like GTPase), which contains tandemly repeated GTP-binding domains, has been shown to play an essential role in 50S ribosomal subunit biogenesis. The depletion of Der results in the accumulation of precursors of 50S ribosomal subunits that are structurally unstable at low Mg(2+) concentrations. Der homologs are ubiquitously found in eubacteria. Conversely, very few are conserved in eukaryotes, and none is conserved in archaea. In the present study, to verify their conserved role in bacterial 50S ribosomal subunit biogenesis, we cloned Der homologs from two gammaproteobacteria, Klebsiella pneumoniae and Salmonella enterica serovar Typhimurium; two pathogenic bacteria, Staphylococcus aureus and Neisseria gonorrhoeae; and the extremophile Deinococcus radiodurans and then evaluated whether they could functionally complement the E. coli der-null phenotype. Only K. pneumoniae and S Typhimurium Der proteins enabled the E. coli der-null strain to grow under nonpermissive conditions. Sucrose density gradient experiments revealed that the expression of K. pneumoniae and S Typhimurium Der proteins rescued the structural instability of 50S ribosomal subunits, which was caused by E. coli Der depletion. To determine what allows their complementation, we constructed Der chimeras. We found that only Der chimeras harboring both the linker and long C-terminal regions could reverse the growth defects of the der-null strain. Our findings suggest that ubiquitously conserved essential GTPase Der is involved in 50S ribosomal subunit biosynthesis in various bacteria and that the linker and C-terminal regions may participate in species-specific recognition or interaction with the 50S ribosomal subunit. IMPORTANCE: In Escherichia coli, Der (double Era-like GTPase) is an essential GTPase that is important for the production of mature 50S ribosomal subunits. However, to date, its precise role in ribosome biogenesis has not been clarified. In this study, we used five Der homologs from gammaproteobacteria, pathogenic bacteria, and an extremophile to elucidate their conserved function in 50S ribosomal subunit biogenesis. Among them, Klebsiella pneumoniae and Salmonella enterica serovar Typhimurium Der homologs implicated the participation of Der in ribosome assembly in E. coli Our results show that the linker and C-terminal regions of Der homologs are correlated with its functional complementation in E. coli der mutants, suggesting that they are involved in species-specific recognition or interaction with 50S ribosomal subunits.

Inhibitory effect of UvrD and DinG on the replication of ColE1-derived plasmids in Escherichia coli.

CspA has been identified as a major cold-shock protein in Escherichia coli. CspA binds to RNAs which are abnormally folded at low temperature and then acts as an RNA chaperone unfolding those RNAs. The dramatic expression of cspA at low temperature is contributed by posttranscriptional stability and robust translatability. Interestingly, when cspA mRNA encoding a premature nonsense codon was overexpressed at low temperature, cell growth was completely inhibited. This phenotype was termed LACE (the low temperature-dependent antibiotic effect of truncated cspA expression), and this lethality resulted from exclusive stalling of most ribosomes on mutant cspA mRNAs. In a previous study, we demonstrated that overexpression of the ATP-dependent DNA helicases, UvrD and DinG, suppressed the lethality and ribosome stalling caused by mutant cspA mRNA. In the present study, we attempted to elucidate how these two DNA helicases help recover normal growth under LACE condition. Interestingly, we found that UvrD and DinG appeared to have an ability to down-regulate the replication of pUC-based high copy plasmid. In plasmid copy number tests, the amount of pUC-based plasmid encoding mutant cspA was reduced by 3-10-fold when either UvrD or DinG was expressed. Through a ß-galactosidase activity assay, we also confirmed that expression of the lacZα gene inserted into the pUC-based plasmid was significantly reduced due to down-regulation of plasmid replication. Our findings imply that UvrD and DinG, known as non-replicative helicases, play a novel role in the regulation of ColE1-like plasmid replication.

Viscosity of dysphagia-oriented cold-thickened beverages: effect of setting time at refrigeration temperature.

BACKGROUND: Although extensive literature is available on the viscosity of thickened beverages with food thickeners, no attempt has been made to study the effect of setting time on the viscosity of pudding-like cold-thickened beverages with xanthan gum (XG)-based thickeners by using a rheometer. In particular, it is of considerable practical importance to investigate the effect of setting time on their viscosity at 5°C because some cold-thickened beverages will be prepared in the kitchen in bulk and stored at 5°C before serving or consuming rather than serving immediately upon mixing with thickeners. AIMS: To examine the effect of different setting times (15-120 min) on the viscosity of cold-thickened beverages prepared with various XG-based food thickeners, and also to compare the viscosity differences among the various cold beverages and XG-based food thickeners in beverage-thickener mixture systems. METHODS & PROCEDURES: Four commercially available XG-based food thickeners (A-D) and three cold beverages (water, orange juice and milk) were used for the preparation of cold-thickened beverages. The thickened sample was portioned into six samples for the designated setting times and then stored at 5°C over setting time. Their apparent viscosity (η(a,50)) at 50 s(-1) was measured using a rheometer. OUTCOMES & RESULTS: The largest increases in η(a,50) values for thickened beverages, except for water, were observed at 15 min (p < 0.05), showing a pudding-like fluid, and at longer time periods their η(a,50) values gradually increased or were constant with an increase in setting time. The percentage increase in viscosity values at different setting times (15-120 min) as compared with the control (0 min) was less pronounced in the thickened orange juice and milk samples with thickener A over setting time, indicating that the thickened beverages with thickener A had more stable structure compared with those with other thickeners (B-D) over time. Statistical analysis showed that changes in the viscosity of cold-thickened beverages over setting time are greatly influenced by the type of beverages and thickeners. CONCLUSIONS & IMPLICATIONS: Cold-thickened beverages should be carefully prepared with instant commercial XG-based food thickeners because they produced different thickening patterns over setting time which clinicians must consider for a safe and easy swallowing. The information presented in this study will provide both clinicians and patients with additional knowledge to prepare cold-thickened beverages with the corrected viscosity for safe swallowing.

Electrostatic interaction-induced inclusion body formation of glucagon-like peptide-1 fused with ubiquitin and cationic tag.

In an attempt to produce glucagon-like peptide-1 (GLP-1) using recombinant Escherichia coli, ubiquitin (Ub) as a fusion partner was fused to GLP-1 with the 6-lysine tag (K6) for simple purification. Despite the high solubility of ubiquitin, the fusion protein K6UbGLP-1 was expressed mainly as insoluble inclusion bodies in E. coli. In order to elucidate this phenomenon, various N- and C-terminal truncates and GLP-1 mutants of K6UbGLP-1 were constructed and analyzed for their characteristics by various biochemical and biophysical methods. The experiment results obtained in this study clearly demonstrated that the insoluble aggregation of K6UbGLP-1 was attributed to the electrostatic interaction between the N-terminal 6-lysine tag and the C-terminal GLP-1 before the completion of folding which might be one of the reasons for protein misfolding frequently observed in many foreign proteins introduced with charged amino acid residues such as the His tag and the protease recognition sites. The application of a cation exchanger for neutralizing the positive charge of the 6-lysine tag in solid-phase refolding of K6UbGLP-1 successfully suppressed the electrostatic interaction-driven aggregation even at a high protein concentration, resulting in properly folded K6UbGLP-1 for GLP-1 production.

Production and solid-phase refolding of human glucagon-like peptide-1 using recombinant Escherichia coli.

Human glucagon-like peptide-1 (GLP-1), an incretin hormone with pharmaceutical potential in treating type 2 diabetes mellitus is known to be rapidly degraded when expressed in Escherichia coli. For the efficient production of the intact GLP-1 using a recombinant E. coli system, a fusion protein of GLP-1 was designed to be composed of the 6-lysine tag, ubiquitin and GLP-1 (K6UbGLP-1) in a row. A fed-batch fermentation of recombinant E. coli BL21(DE3)/pAPK6UbGLP-1 was carried out in a pH-stat feeding strategy and resulted in 11.3 g/L of K6UbGLP-1 as a form of inclusion body. Solid-phase refolding of K6UbGLP-1 inclusion body using a cation exchanger of the SP Sepharose FF led to a refolding yield over 90% even at 5.2 mg protein/mL resin. On-column cleavage of the refolded K6UbGLP-1 with ubiquitin-specific protease 1 gave an authentic form of GLP-1. Instrumental analyses using mass spectrometry and reverse-phase HPLC showed that the recombinant GLP-1 released from K6UbGLP-1 was identical to the standard GLP-1.

Mimicking cotranslational folding of prosubtilisin E in vitro.

Nascent polypeptides are synthesized on ribosomes starting at the N-terminus and simultaneously begin to fold during translation. We constructed N-terminal fragments of prosubtilisin E containing an intramolecular chaperone (IMC) at N-terminus to mimic cotranslational folding intermediates of prosubtilisin. The IMC-fragments of prosubtilisin exhibited progressive enhancement of their secondary structures and thermostabilities with increasing polypeptide length. However, even the largest IMC-fragment with 72 residues truncated from the C-terminus behaved as a molten globule, indicating the requirement of the C-terminal region to have a stable tertiary structure. Furthermore, truncation of the IMC in the IMC-fragments resulted in aggregation, suggesting that the IMC plays a crucial role to prevent misfolding and aggregation of cotranslational folding intermediates during translation of prosubtilisin polypeptide.

Cynandione A from Cynanchum wilfordii inhibits hepatic de novo lipogenesis by activating the LKB1/AMPK pathway in HepG2 cells.

Cynandione A (CA), isolated from ethyl acetate extract of Cynanchum wilfordii (CW), is a bioactive phytochemical that has been found to be beneficial for the treatment of several diseases. Hepatic de novo lipogenesis is one of the main causes of non-alcoholic fatty liver disease (NAFLD), which is thought to be a hepatic manifestation of certain metabolic syndromes. However, it has not yet been reported if CA has any therapeutic value in these diseases. Here, we investigated whether CA can inhibit hepatic lipogenesis induced by liver X receptor α (LXRα) using an in vitro model. We found that the extract and ethyl acetated layer of CW decreased the mRNA levels of sterol regulatory element-binding protein-1c (SREBP-1c), which plays a crucial role in hepatic lipogenesis. Additionally, we observed that CA could suppress the level of SREBP-1c, which was increased using two commercial LXRα agonists, GW3954 and T0901317. Moreover, the enzymes that act downstream of SREBP-1c were also inhibited by CA treatment. To understand the mechanism underlying this effect, the levels of phosphorylated AMP kinase (pAMPK) were measured after CA treatment. Therefore, CA might increase the pAMPK level by inducing phosphorylation of liver kinase B1 (LKB1), which can then convert AMPK to pAMPK. Taken together, we conclude that CA has an alleviative effect on hepatic lipogenesis through the stimulation of the LKB1/AMPK pathway.

Production of membrane proteins for NMR studies using the condensed single protein (cSPP) production system.

In the Single Protein Production (SPP) method, all E. coli cellular mRNAs are eliminated by the induction of MazF, an ACA-specific mRNA interferase. When an mRNA for a membrane protein, engineered to have no ACA sequences without altering its amino acid sequence, is induced in the MazF-induced cells, E. coli is converted into a bioreactor producing only the targeted membrane protein. Here we demonstrate that three prokaryotic inner membrane proteins, two prokaryotic outer membrane proteins, and one human virus membrane protein can be produced at very high levels, and assembled in appropriate membrane fractions. The condensed SPP (cSPP) system was used to selectively produce isotope-enriched membrane proteins for NMR studies in up to 150-fold condensed culture without affecting protein yields, providing more than 99% cost saving for isotopes. As a novel application of the cSPP system for studies of membrane proteins prior to purification we also demonstrate, for the first time, fast detergent screening by microcoil NMR and well-resolved NMR spectra of several targeted integral membrane proteins obtained without purification.

Folding machineries displayed on a cation-exchanger for the concerted refolding of cysteine- or proline-rich proteins.

BACKGROUND: Escherichia coli has been most widely used for the production of valuable recombinant proteins. However, over-production of heterologous proteins in E. coli frequently leads to their misfolding and aggregation yielding inclusion bodies. Previous attempts to refold the inclusion bodies into bioactive forms usually result in poor recovery and account for the major cost in industrial production of desired proteins from recombinant E. coli. Here, we describe the successful use of the immobilized folding machineries for in vitro refolding with the examples of high yield refolding of a ribonuclease A (RNase A) and cyclohexanone monooxygenase (CHMO). RESULTS: We have generated refolding-facilitating media immobilized with three folding machineries, mini-chaperone (a monomeric apical domain consisting of residues 191-345 of GroEL) and two foldases (DsbA and human peptidyl-prolyl cis-trans isomerase) by mimicking oxidative refolding chromatography. For efficient and simple purification and immobilization simultaneously, folding machineries were fused with the positively-charged consecutive 10-arginine tag at their C-terminal. The immobilized folding machineries were fully functional when assayed in a batch mode. When the refolding-facilitating matrices were applied to the refolding of denatured and reduced RNase A and CHMO, both of which contain many cysteine and proline residues, RNase A and CHMO were recovered in 73% and 53% yield of soluble protein with full enzyme activity, respectively. CONCLUSION: The refolding-facilitating media presented here could be a cost-efficient platform and should be applicable to refold a wide range of E. coli inclusion bodies in high yield with biological function.

Comprehensive analysis of excision repair complementation group 1, glutathione S-transferase, thymidylate synthase and uridine diphosphate glucuronosyl transferase 1A1 polymorphisms predictive for treatment outcome in patients with advanced gastric cancer treated with FOLFOX or FOLFIRI.

Oxaliplatin and irinotecan have proven effective in the treatment of gastric cancer. We attempted to determine whether single nucleotide polymorphisms in ERCC1, GST, TS and UGT1A1 predicted overall survival in gastric cancer patients receiving FOLFOX and/or FOLFIRI chemotherapy. Total genomic DNA was extracted from the whole blood of patients. The PCR-restriction fragment length polymorphism technique was applied in order to detect the known variant sites of ERCC1, GST, TS and UGT1A1. The response rate of FOLFOX (N=75) was 24%. Grade 3-4 neutropenia and neurotoxicity were observed at frequencies of 34.7 and 16%, respectively. TTP and OS of first-line administration of FOLFOX (N=35) were 3.1 months (95% CI, 0.1-6.1 months) and 13.9 months (95% CI, 12.2-15.6 months), respectively. Only the GSTM1 positive genotype exhibited a significantly better time to progression (P=0.023). However, significant genotypic variation of TS, GST and ERCC1, which was assumed to affect the activity of oxaliplatin, was not observed to affect RR, toxicity and overall survival. The response rate of FOLFIRI (N=74) was 23%. Grade 3-4 neutropenia and diarrhea were observed in 55.4 and 9.5% of cases, respectively. TTP and OS of first-line administration of FOLFIRI (N=33) was 4.9 months (95% CI, 3.5-6.4 months) and 19.0 months (95% CI, 8.5-29.5 months). The low expression type (2R/2R, 2R/3C and 3C/3C) of TS was associated with a high incidence of grade >or=3 neutropenia. However, significant genotypic variation of UGT1A1, which was assumed to affect irinotecan toxicity, was not observed to affect RR, toxicity or survival. In this study, the GSTM1 positive genotype evidenced a significantly better time to progression in cases of advanced gastric cancer being treated with FOLFOX. The low expression type (2R/2R, 2R/3C and 3C/3C) of TS was associated with a high incidence of grade >or=3 neutropenia in cases of advanced gastric cancer treated with FOLFIRI.

Inhibitory effect of α-amyrin acetate isolated from Fraxinus rhynchophylla on Th17 polarization.

BACKGROUND: T helper 17 (Th17) cells, which are differentiated from CD4+ T cells, drive inflammation, leading to autoimmune diseases such as psoriasis, rheumatoid arthritis, and inflammatory bowel disease. Therefore, inhibiting Th17 polarization could be a therapeutic target for inflammatory diseases. PURPOSE: We investigated the inhibitory effect of Fraxinus rhynchophylla (Oleaceae) on Th17 differentiation and found its active component. STUDY DESIGN: The activity of F. rhynchophylla and its active constituent was verified using CD4+ cells extracted from C57BL/6 mice. METHODS: Micro-environment for Th17 polarization was provided to CD4+ cells and the effect of treatment with samples was measured by enzyme linked immunosorbent assay (ELISA), polymerase chain reaction (PCR), and Western blot. RESULTS: The extract of F. rhynchophylla Hance and its chemical constituent, α-amyrin acetate, which was isolated via bioassay-guided isolation, significantly inhibited Th17 polarization as revealed when interleukin (IL)-17, a characteristic cytokine produced by Th17 cells, was measured. Furthermore, the inhibitory effect of α-amyrin acetate was compared to the amyrin derivatives, α-amyrin and ß-amyrin. All displayed a suppressive effect on Th17 polarization and all reduced the expression of single transducer and activator of transcription 3 (STAT3) and retinoic acid receptor-related orphan receptor γt (RORγt), which are crucial transcription factors regulating Th17 differentiation. α-Amyrin acetate, however, exhibited the most prominent effects, which indicates that the functional group, acetate, might strengthen the inhibitory effect on Th17 differentiation. CONCLUSION: Taken together, these results suggest that the extract of F. rhynchophylla and its active constituent, α-amyrin acetate, could be applied as a potential therapeutic agent for autoimmune disorders such as rheumatoid arthritis.

Proteome analysis of recombinant Escherichia coli producing human glucagon-like peptide-1.

The proteomic response of recombinant Escherichia coli producing human glucagon-like peptide-1 was analyzed by two-dimensional gel electrophoresis. Protein spots in two-dimensional gel could be identified by using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and their expression profiles were compared with those of nonproducing cells. Thirty-five intracellular proteins exhibited differential expression levels between the production and control strains. These changes reflected physiological responses to heterologous peptide production in recombinant E. coli. Specifically, physiological changes included the down-regulation of proteins involved in the central carbon metabolism, biosynthesis of cellular building blocks and peptides, and up-regulation of cell protection proteins and some sugar transport proteins. This comprehensive analysis would provide useful information for understanding physiological alterations to heterologous peptide production and for designing efficient metabolic engineering strategies for the production of recombinant peptides in E. coli.

Translation-dependent mRNA cleavage by YhaV in Escherichia coli.

Many bacteria have toxin-antitoxin (TA) systems, where toxin gene expression inhibits their own cell growth. mRNA is one of the well-known targets of the toxins in the type II toxin-antitoxin systems. Here, we examined the ribosome dependency of the endoribonuclease activity of YhaV, one of the toxins in type II TA systems, on mRNA in vitro and in vivo. A polysome profiling assay revealed that YhaV is bound to the 70S ribosomes and 50S ribosomal subunits. Moreover, we found that while YhaV cleaves ompF and lpp mRNAs in a translation-dependent manner, they did not cleave the 5' untranslated region in primer extension experiments. From these results, we conclude that YhaV is a ribosome-dependent toxin that cleaves mRNA in a translation-dependent manner.

Affinity improvement by fine tuning of single-chain variable fragment against aflatoxin B1.

Aflatoxin B1 (AFB1) produced in Aspergillus flavus is a major hepatocarcinogen found in foods and feed. For effective immunological detection of AFB1 at low concentrations, the development of high affinity antibody for AFB1 is required. Previously, an affinity-maturated single-chain variable fragment containing 6 mutations (scFv-M37) was isolated from an artificial mutagenic library, which showed a 9-fold higher affinity than its wild type scFv. In this study, the effect of the 6 mutated residues on the affinity improvement was characterized using surface plasmon resonance analysis, which identified a deleterious mutation (VH-A110T) located on a framework region of the scFv-M37. The back mutation of VH-A110T resulted in a 3.2-fold affinity improvement, which was attributed to decrease of dissociation rate constant (kd) in interaction between AFB1 and the back mutant scFv. The biophysical analyses using circular dichroism and gel filtration revealed that the back mutation of VH-A110T caused a subtle conformational change of the scFv toward tighter binding to AFB1.

Affinity maturation of single-chain variable fragment specific for aflatoxin B(1) using yeast surface display.

As aflatoxin B1 is one of the most toxic mycotoxins, it is important to detect and to quantify aflatoxin B1 accurately by immunological methods. To enhance aflatoxin B1-binding affinity of the single-chain variable fragment, yeast surface display technique combined with fluorescence-activated cell sorting was applied. A randomly mutated scFv library was subjected to 4 rounds of fluorescence-activated cell sorting, resulting in isolation of 5 scFv variants showing an affinity improvement compared to the parental wild type scFv. The best scFv with a 9-fold improvement in affinity for aflatoxin B1 exhibited similar specificity to the monoclonal antibody. Most of the mutations in scFv-M37 were located outside of the canonical antigen-contact loops, suggesting that its affinity improvement might be driven by an allosteric effect inducing scFv-M37 to form a more favorable binding pocket for aflatoxin B1 than the wild type scFv.