A világ természetes dolgai: Svitel Zsuzsa monológja

Én nem vagyok határozottan tervező valaki, inkább belesodródom a dolgokba. Ugyanakkor a természetemből adódik az is, hogy nagyon vállalkozó kedvű vagyok, nem egykönnyen ijedek meg. Naivan élem meg az életet, mindent elképzelhetőnek tartok. Számomra ugyanolyan kalandos egy párizsi irodában nyolc órát ülni, mint Thaiföldön egy kolostorban vagy Indiában egy szegénytelepen lenni. Ezek a dolgok egyforma megmérettetéseknek számítanak. Vak lennék, ha nem látnám, hogy ez már ötéves koromtól így van, hiszen lány létemre futballoztam, s tizennyolc éves koromban disszidáltam Magyarországról. Szóval izgága vagyok, kíváncsi, szeretem az életet. Nem hiszem, hogy különösebben okos volnék. Viszont a dolgokat megélni nagyon jól tudom, és a bátorságom is megvan hozzá. Emellett rendkívül szívós is vagyok. (...

Kinetic and thermodynamic characterization of single-mismatch discrimination using single-molecule imaging

A single-molecule detection setup based on total internal reflection fluorescence (TIRF) microscopy has been used to investigate association and dissociation kinetics of unlabeled 30mer DNA strands. Single-molecule sensitivity was accomplished by letting unlabeled DNA target strands mediate the binding of DNA-modified and fluorescently labeled liposomes to a DNA-modified surface. The liposomes, acting as signal enhancer elements, enabled the number of binding events as well as the residence time for high affinity binders (Kd < 1 nM, koff < 0.01 s−1) to be collected under equilibrium conditions at low pM concentrations. The mismatch discrimination obtained from the residence time data was shown to be concentration and temperature independent in intervals of 1–100 pM and 23–46°C, respectively. This suggests the method as a robust means for detection of point mutations at low target concentrations in, for example, single nucleotide polymorphism (SNP) analysis

Kinetics and thermodynamics of DNA hybridization on gold nanoparticles

Hybridization of single-stranded DNA immobilized on the surface of gold nanoparticles (GNPs) into double stranded DNA and its subsequent dissociation into ssDNA were investigated. Melting curves and rates of dissociation and hybridization were measured using fluorescence detection based on hybridization-induced fluorescence change. Two distribution functions, namely the state distribution and the rate distribution, were proposed in order to take interfacial heterogeneity into account and to quantitatively analyze the data. Reaction and activation enthalpies and entropies of DNA hybridization and dissociation on GNPs were derived and compared with the same quantities in solution. Our results show that the interaction between GNPs and DNA reduces the energetic barrier and accelerates the dissociation of adhered DNA. At low surface densities of ssDNA adhered to GNP surface, the primary reaction pathway is that ssDNA in solution first adsorbs onto the GNP, and then diffuses along the surface until hybridizing with an immobilized DNA. We also found that the secondary structure of a DNA hairpin inhibits the interaction between GNPs and DNA and enhances the stability of the DNA hairpin adhered to GNPs

Facile detection of proteins on a solid-phase membrane by direct binding of dextran-based luminol?biotin chemiluminescent polymer

Facile and non-radioactive methods are desired for the sensitive detection and quantification of various proteins. Herein we describe a novel chemiluminescence (CL)-detection method of particular proteins based on direct binding of a dextran-luminol-biotin (DLB) CL polymer to the proteins on a poly(vinylidene difluoride) membrane. Among 32 kinds of the proteins screened, several proteins such as drug-metabolizing enzymes, cytochrome p450 (CYP)1A2, CYP2E1, and CYP3A4 had the ability to bind directly to the DLB polymer. The binding site in the polymer was owing to the framework of the modified dextran, which underwent oxidation and reduction procedures. This interaction might be the comprehensive effect of both electrostatic interaction and steric complementarities. CL intensity of the proteins detected by the polymer could be further enlarged by the mediation of avidin. The proposed CL-imaging method possesses potential as a rapid, facile, inexpensive and selective detection of the proteins

Gefitinib Induces Epidermal Growth Factor Receptor Dimers Which Alters the Interaction Characteristics with 125I-EGF

The tyrosine kinase inhibitor gefitinib inhibits growth in some tumor types by targeting the epidermal growth factor receptor (EGFR). Previous studies show that the affinity of the EGF-EGFR interaction varies between hosting cell line, and that gefitinib increases the affinity for some cell lines. In this paper, we investigate possible mechanisms behind these observations. Real-time interaction analysis in LigandTracer® Grey revealed that the HER2 dimerization preventing antibody pertuzumab clearly modified the binding of 125I-EGF to EGFR on HER2 overexpressing SKOV3 cells in the presence of gefitinib. Pertuzumab did not affect the binding on A431 cells, which express low levels of HER2. Cross-linking measurements showed that gefitinib increased the amount of EGFR dimers 3.0–3.8 times in A431 cells in the absence of EGF. In EGF stimulated SKOV3 cells the amount of EGFR dimers increased 1.8–2.2 times by gefitinib, but this effect was cancelled by pertuzumab. Gefitinib treatment did not alter the number of EGFR or HER2 expressed in tumor cell lines A431, U343, SKOV3 and SKBR3. Real-time binding traces were further analyzed in a novel tool, Interaction Map, which deciphered the different components of the measured interaction and supports EGF binding to multiple binding sites. EGFR and HER2 expression affect the levels of EGFR monomers, homodimers and heterodimers and EGF binds to the various monomeric/dimeric forms of EGFR with unique binding properties. Taken together, we conclude that dimerization explains the varying affinity of EGF – EGFR in different cells, and we propose that gefitinib induces EGFR dimmers, which alters the interaction characteristics with 125I-EGF

Influence of mannan epitopes in glycoproteins - Concanavalin A interaction. Comparison of natural and synthetic glycosylated proteins

Two natural glycoproteins/glycoenzymes, invertase and glucoamylase, and two neoglycoconjugates, synthetized from Saccharomyces cerevisiae mannan, bovine serum albumin and penicillin G acylase were tested for interaction with lectin Concanavalin A (Con A). The interaction of natural and synthetic glycoproteins with Con A was studied using three different experimental methods: (i) quantitative precipitation in solution (ii) sorption to Con A immobilized on bead cellulose; and (iii) kinetic measurement of the interaction by surface plasmon resonance. Prepared neoglycoproteins were further characterized: saccharide content, molecular weight, polydispersion, kinetic and equilibrium association constants with Con A were determined. It can be concluded that the used conjugation method proved to be able to produce neoglycoproteins with similar properties like natural glycoproteins, i.e. enzymatic activity (protein part) and lectin binding activity (mannan part) were preserved and the neoglycoconjugates interact with Con A similarly as natural mannan-type glycoproteins

Development of a flow injection capillary chemiluminescent ELISA using an imprinted polymer instead of the antibody

A flow injection competitive assay analogous to enzyme immunoassays has been developed using a molecularly imprinted polymer instead of the antibody. A glass capillary was modified by covalently attaching an imprinted polymer to the inner capillary wall. The herbicide 2,4-dichlorophenoxyacetic acid was used as a model analyte. The analyte was labeled with tobacco peroxidase, and chemiluminescence was used for detection in combination with a photomultiplier tube or a CCD camera. In a competitive mode, the analyte-peroxidase conjugate was passed together with the free analyte through the polymer-coated capillary mounted in a flow system. After a washing step, the chemiluminescent substrate was injected and the bound fraction of the conjugate was quantified by measuring the intensity of the emitted light. Calibration curves corresponding to analyte concentrations ranging from 0.5 ng mL-1 to 50 μg mL-1 (2.25 nM-225 μM) were obtained. A lowered detection limit by 2 orders of magnitude was obtained when detection was done in discontinuous mode and the chemiluminescence light was conducted inside the photomultiplier tube by an optical fiber bundle, thus yielding a dynamic range of 5 pg mL-1-100 ng mL-1 (22.5 pM-450 nM)