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An oblique impinging-jet (OBIJ) cell was developed, suitable for colloid deposition studies at various interfaces including the practically significant case of non-transparent substrates. Particle transport conditions in the cell were quantitatively evaluated by studying kinetics of polystyrene latex particle deposition on mica. The dependence of the reduced particle flux (mass transfer coefficient) on the flow Reynolds number (Re) was determined by in situ microscope enumeration of adsorbed particles. It was demonstrated, in accordance with previous results for the orthogonal impinging-jet cell, that the flux increased significantly with the Re number. This was interpreted in terms of the convective diffusion theory incorporating the hydrodynamic and specific interactions. The governing transport equation originating from this theory was solved numerically, for the region near the stagnation point, by using the finite-difference method. These numerical solutions were used for nonlinear fitting of the flow intensity parameter α dependence on the Re number. In this way, the transport conditions in the vicinity of the stagnation point were fully characterized. The method was applied for studying kinetics of latex adsorption on non-transparent, plasma treated polymeric substrates. It was demonstrated that a prolonged treatment (ca. 20 min) enhanced considerably particle deposition rate that attained values pertinent to the model mica substrate.

This report describes the crystal structure of the K(+) channel-blocking toxin, BmBKTx1, isolated recently from the venom of the scorpion Buthus martensi Karsch. This is only the second structure of the short-chain K(+) channel-blocking toxin from scorpion solved by means of X-ray crystallography. Additionally, reductive dimethylation of folded BmBKTx1 employed to induce its crystallization and solution of the structure based on the anomalous signal from the sulfur atoms make this example quite unique. The monomer of BmBKTx1 is formed by 31 amino acid residues, including 6 cysteines connected in 3 disulfide bridges. Crystals of this toxin belong to the space group P2(1) with two molecules present in the asymmetric unit. The unit cell parameters are a = 21.40 A, b=39.70 A, c=29.37 A, and beta-94.13 grades. Based on the high-quality dataset (anomalous signal) collected to the resolution 1.72A using the conventional X-radiation generator (lambda Cu, K alpha = 1.5478 A), the positions of sulfur atoms contributed by 12 cysteine residues have been identified, and subsequent improvement of the experimental phases have allowed structure solution. The final model was refined to the crystallographic R-factor of 0.166. The methyl groups on several lysine residues could be easily modeled into the electron density.

A sensitive capillary electrophoresis mobility shift assay (CEMSA) for qualitative study of the interaction between the trans-activation response element (TAR) and the trans-activator of transcription protein (Tat) has been presented. The human immunodeficiency virus type 1 (HIV-1) Tat promotes elongation of viral mRNAs binding to the TAR. It has been suggested 52 that a single, conserved arginine residue (presumably Arg ) within the arginine-rich region (ARR) of Tat plays the major 52 role for the Tat-TAR recognition. To study structural requirements of the Arg position, Tat(49-57)-NH analogues 2 52 substituted with nonencoded amino acids at the Arg position have been synthesized and their interaction with TAR has been studied by CEMSA. Using a linear polyacrylamide-coated capillary and a sieving polymer containing separation buffer, well separated and shaped peaks of free and bound TAR RNA were obtained. In the presence of Tat1 peptide bearing the native sequence of Tat(49-57) a significant shift of migration time of TAR from 18.66 min (RSD 51.4%) to 20.12 min 52 (RSD52.4%) was observed. We have found that almost every substitution within the guanidino group of the Arg 52 (L-Arg → Cit, → Orn, → Arg(NO ), → Arg(Me )) strongly disrupted or abolished the TAR-Tat peptide interaction. 22 52 Enantiomeric substitution, L-Arg → D-Arg was the only one which notably promoted TAR-Tat peptide interaction. The 52 results demonstrate that the specific net of hydrogen bonds created by the guanidinio group of conserved Arg plays a crucial role for TAR-Tat HIV-1 recognition. The newly developed procedure describes for the first time use of CE to monitor RNA-peptide complex formation. The methodology presented should be generally applicable to study RNA- peptide (protein) interaction.  2002 Elsevier Science B.V. All rights reserved.

We investigate the lateral diffusion of Human Serum Albumin−Fluorescein Isothiocyanate (HSA) adsorbed “on” or embedded “in” poly(sodium 4-styrenesulfonate)/poly(allylamine hydrochloride) (PSS/PAH) multilayers. Special attention is brought to the evolution of the diffusion coefficient with the surface HSA concentration. We find that while on PSS terminating films the diffusion coefficient of adsorbed HSA is independent of the protein surface concentration in the explored range, it decreases strongly with the surface concentration when HSA is adsorbed on PAH ending films. On both films, the mobile fraction of adsorbed protein molecules decreases when the surface concentration increases. At low surface coverage, up to 90% of the adsorbed protein molecules are mobile both on PSS and PAH terminating films. The decrease of the mobile fraction with the HSA surface concentration is more pronounced on PSS than on PAH reaching, respectively, 50% and 70% of mobile HSA molecules at high surface coverage. This behavio...

A sensitive capillary electrophoresis mobility shift assay (CEMSA) to analyze RNA/peptide interactions has been developed. Capillary electrophoresis (CE) has been adapted for investigating the interaction between variously methylated 17-nt analogs of the yeast tRNAPhe anticodon stem and loop domain (ASL(Phe)) and 15-amino-acid peptides selected from a random phage display library (RPL). A peptide-concentration-dependent formation of RNA/peptide complex was clearly visible during CEMSA. In the presence of peptide, the UV-monitored CE peak for ASLPhe with three of the five naturally occurring modifications (2'-O-methylcytidine (Cm32), 2'-O-methylguanine (Gm34) and 5-methylcytidine (m5C40) shifted from 18.16 to 20.90 min. The mobility shift was observed only for methylated RNA. The negative effects of diffusion, electroosmotic flow and adhesion of molecules to the capillary internal wall were suppressed by using a buffer containing a sieving polymer and a polyacrylamide-coated capillary. Under these conditions, well-shaped peaks and resolution of RNA free and bound to peptide were achieved. Peptide tF2, the most populated ligand in the RPL, specifically bound triply methylated ASLPhe in a methylated nucleoside-dependent manner. CE was found to be an efficient and sensitive method for the qualitative analysis of RNA-peptide interaction and should be generally applicable to the study of RNA-peptide (protein) interactions.

It has been generally expected that the most applicable drug delivery system (DDS) should be biodegradable, biocompatible and with incidental adverse effects. Among many micellar aggregates and their mediated polymeric systems, polyelectrolyte oil-core nanocarriers have been found to successfully encapsulate hydrophobic drugs in order to target cells and avoid drug degradation and toxicity as well as to improve drug efficacy, its stability, and better intracellular penetration. This paper reviews recent developments in the formation of polyelectrolyte oil-core nanocarriers by subsequent multilayer adsorption at micellar structures, their imaging, physical state and stability, drug encapsulation and applications, in vitro release profiles and in vitro biological evaluation (cellular uptake and internalization, biocompatibility). We summarize the recent results concerning polyelectrolyte/surfactant interactions at interfaces, fundamental to understand the mechanisms of formation of stable polyelectrolyte layered structures on liquid cores. The fabrication of emulsion droplets stabilized by synergetic surfactant/polyelectrolyte complexes, properties, and potential applications of each type of polyelectrolyte oil-core nanocarriers, including stealth nanocapsules with pegylated shell, are discussed and evaluated.

We present the first results relative to the diffusion process of proteins (human serum albumin) adsorbed on or embedded in poly(sodium 4-styrenesulfonate)/poly(allylamine hydrochloride) polyelectrolyte multilayer films by using fluorescence recovery after photobleaching. At least two populations of adsorbed proteins exist on the top or within the multilayer architectures. One population, which typically represents 50-70% of the adsorbed proteins, corresponds to proteins that are able to diffuse laterally along the surface or in the multilayers, whereas the others diffuse more slowly or seem almost immobile over the experimental time scale. This constitutes a key result for the practical applications of the polyelectrolyte multilayers as targeted biomaterial coatings. Surprisingly, the diffusion coefficients of the mobile proteins that are embedded in the multilayers are comparable with the diffusion coefficients of the mobile proteins adsorbed on top of the multilayers. The diffusion coefficients, which are 1 order of magnitude smaller than on rigid substrates such as silica or poly(methyl methacrylate), are of the order of 10-10 and 10-11 cm2/s.

Thin films containing casein appear to be a promising material for coatings used in the medical area to promote biomineralization. alfa- and beta-casein and poly-L-arginine multilayer films were formed by the layer-by layer technique and their thickness and mass were analyzed by ellipsometry and quartz crystal microbalance with dissipation monitoring (QCM-D). We investigated the effect of the type of casein used for the film formation and of the polyethyleneimine anchoring layer on the thickness and mass of adsorbed films. The analysis of the mass of films during their post-treatment with the solutions of various ionic strength and pH provided the information concerning films stability, while the XPS elemental analysis confirmed binding of calcium ions by the casein embedded in the multilayers., 7 pages, 10 figures, prepared to publish in Journal of Colloid and Interface Science

Fluctuations in the number of colloid particles adsorbed irreversibly under pure diffusion transport conditions were determined as a function of surface density and ionic strength of the suspension. The experiments were carried out for monodisperse polystyrene latex particles of micrometer size range adsorbing irreversibly at mica surface. The surface density of adsorbed particles at various areas was determined using the direct microscope observation method. A new experimental cell was used enabling in situ observations of particles adsorption under conditions of negligible gravity effects. It was found that the particle density fluctuations for high ionic strength were in a good agreement with the theoretical results derived from the random sequential adsorption (RSA) model. Also, the theoretical results stemming from the equilibrium scaled particle theory reflected the experimental data satisfactorily. For lower ionic strength a deviation from the hard sphere behavior was experimentally demonstrated. This effect due to the repulsive electrostatic interactions was interpreted in terms of the effective hard particle concept. The universal dependence of variance on particle density obtained in this way was found in a good agreement with the RSA model for all ionic strength. These results proved that fluctuations in particle density of monolayer formed under diffusional conditions differ fundamentally from these obtained under ballistic transport conditions.

Galanin (Gal) constricts rat gastric fundus by acting on receptors located in the cell membrane. We compared the role of intracellular Ca2+ release with extracellular Ca2+ influx in Gal-stimulated contraction of isolated gastric smooth muscle strips. We also tested if phospholipase C (PLC) or protein kinase C (PKC) participate in the signal transduction cascade. Concentration-contraction curves were constructed non-cumulatively in the presence of atropine, hexamethonium, guanethidine and tetrodotoxin. The half-maximum effective concentration (EC50) of Gal was 21.62nM and Hill's coefficient was 1.02. The effects of Gal were decreased by diltiazem, Ca2+-deficiency in the buffer, Ca2+ removal from the extracellular medium or quercetin. Depletion of intracellular Ca2+-stores, ryanodine and 3,4,5-trimethoxybenzoic acid 8-(diethylamino)-octyl ester diminished the contractile effect of Gal concentration-dependently. Trifluoroperazine and phosphatidylinositol-specific phospholipase C (PI-PLC) inhibitors, neomycin and U-73122, attenuated the gastric fundus response to Gal, whereas phosphatidylcholine-specific phospholipase C (PC-PLC) and phospholipase D (PLD) blockers, D609 and propranolol, were ineffective. The inhibitors of PKC or myosin light chain kinase, calphostin C, chelerythrine, ML-7 and ML-9, lowered the myogenic activity of Gal. Our data confirmed that the stimulation of Gal receptors in gastric fundus is coupled to Ca2+ influx through voltage-dependent channels and intracellular Ca2+ release from ryanodine- and inositol 1,4,5-triphosphate-sensitive stores. Enzymes such as PI-PLC and PKC, but not PC-PLC or PLD, play a role in the signal transduction cascade. Calmodulin and myosin light chain kinase lie downstream of the increases in intracellular Ca2+ concentration evoked by Gal.

Irreversible adsorption (deposition) of negatively charged latex particles on silanized mica was studied by the optical microscopy method. The kinetics of this process, occurring under the diffusion-controlled transport regime, was determined by directly counting the number of particles as a function of adsorption time, reaching 80 h. Measurements were carried out for various ionic strengths of the suspension with the aim of determining both adsorption kinetics and the maximum coverage ϑmx. The experimental data were interpreted in terms of the generalized RSA (random sequential adsorption) theory by considering the bulk transport of particles coupled with the transport through the adsorbed particle layer, forming a steric barrier. The resulting nonlinear boundary value problem was solved numerically by the finite difference method. A quantitative agreement of this model with experimental results was found, in respect to both adsorption kinetics and the maximum surface coverage. In contrast, the Langmuir ...

Recent theoretical and experimental data concerning colloid particle deposition from well-defined flows onto solid/liquid interfaces were reviewed. The macroscopic flow fields in the vicinity of the spherical and cylindrical collector (both isolated and forming a structured layer) were presented. Analogous solutions for the impinging-jet cells of (i) radial symmetry (radial impinging-jet cell RIJ) and (ii) plane symmetry (the slot impinging-jet cell SIJ) were also discussed. Similarities and differences between these flows are pointed out. The method of decomposing the macroscopic flows into local flows of simple geometry like shearing and stagnation flows was exposed. The microscopic flows are discussed in some detail, especially those connected with the motion of a spherical particle parallel and perpendicular to a solid wall. Using the local flow distributions the governing continuity equation is formulated, incorporating the convective transport in the bulk and the specific force dominated transport at the surface. Approximate analytical models aimed at decoupling these transfer steps are described, in particular the surface force boundary layer approximation (SFBLA). Limiting analytical solutions for the perfect sink boundary conditions were given. A procedure of extending the convective diffusion theory to non-linear adsorption regimes governed by the steric barrier due to adsorbed particles, was also presented. The role of the electro-hydrodynamic coupling leading to the hydrodynamic scattering effect in the blocking phenomena was discussed. The theoretical results are confronted with experimental data obtained in the well-defined systems, e.g. mostly in the RIJ and SIJ cells using monodisperse polystyrene latex colloids. A good agreement of theoretical and experimental data was found and most of the theoretical predictions were quantitatively confirmed, in particular the significance of the hydrodynamic scattering effect.

Recently we have sequenced cDNA of plant glutaminyl-tRNA synthetase (GlnRS) from Lupinus luteus. At the N terminal part the protein contains a lysine rich polypeptide (KPKKKKEK), which is identical to a nuclear localization signal (NLS). In this paper we showed that two synthetic peptides (20 and 8 amino acids long), which were derived from lupin GlnRS containing the NLS sequence interact with DNA, but one of them (8aa long) changing its conformation from the B to the Z form. This observation clearly suggests that the presence of the NLS polypeptide in a leader sequence of GlnRS is required not only for protein transport into nucleus but also for regulation of a gene expression. This is the first report suggesting a role of the NLS signal peptide in structural changes of DNA.

An 18-amino acid polypeptide systemin was synthesized by the solid-phase method and its conformation was studied by circular dichroism spectroscopy. The peptide in solution is a mixture of random coil structure with β-sheet and β-turn motifs as has been previously suggested with NMR spectra. Free zone capillary electrophoresis analysis proved purity and chemical stability of systemin at different pH.

The Tat wild-type fragment of sequence Arg49-Lys-Lys-Arg52-Arg-Gln-Arg-Arg-Arg57-NH2 (labelled as Tat1) and three analogues of this fragment with the substitution Arg52 → D-Arg52 (labelled as Tat2) or L-citrulline (Cit) (labelled as Tat3) or L-ornithine (Orn) (labelled as Tat4) were synthesized to study Tat-TAR RNA HIV-1 (27-nucleotide fragment of sequence 5′-AGAUCUGAGCCUGGAGCUCUCU-3′) interactions by circular dichroism. α-helical structure was the most readily adopted by the Tat3 analogue with Arg52 → Cit substitution. All the peptides investigated caused conformational changes in the TAR structure. The most dramatic changes were observed for the Tat2-TAR complex.

Inhibitory effect of galanin on basal and secretagogs-stimulated gastric acid secretion was investigated in urethane-anesthetized rats. A rat stomach was mounted in an ex-vivo chamber, perfused with saline, and either gastric acid or alkaline secretion was determined by titrating the perfusate. Gastric mucosal blood flow (GMBF) was measured by a laser Doppler flowmeter. Intravenous infusion of galanin dose-dependently inhibited the increase of acid secretion induced by pentagastrin and carbachol but not by histamine, without any influence on the GMBF response. Galanin also reduced basal acid secretion while increasing GMBF, but did not evoke any change in basal gastric alkaline secretion. M15, which is a galanin receptor antagonist in the central nervous system but acts as a full agonist in the gastrointestinal smooth muscle, also suppressed pentagastrin-induced acid secretion, similar to galanin. In addition, pentagastrin increased the release of histamine into the gastric lumen, and this response was significantly inhibited by galanin. These results suggest that the inhibitory effect of galanin on acid secretion is mediated by suppression of endogenous histamine release from enterochromaffin-like cells and that the process may be related to the activation of the same subtype of galanin receptors as in the central nervous system and pancreatic β-cells.

The role of the cholinergic and peptidergic pathways in the impairment of gastric motility associated with diabetic gastroparesis was assessed at the postsynaptic level using isolated fundus smooth muscle strips. Maximal contractile responses to carbachol and galanin were significantly decreased in fundus strips isolated from rats rendered diabetic by a single intraperitoneal injection of streptozotocin (STZ, 70 mg/kg) 1, 4 and 8 weeks before experiments. We also observed notable decrements in the slopes and Hill’s coefficients without conspicuous changes in the EC50 of the respective galanin concentration-response curves measured in strips obtained from STZ animals after 4 and 8 weeks. L-NAME reversed the above-mentioned alterations in an L-arginine-sensitive manner in STZ rats after 4 weeks but not in STZ rats after 8 weeks. The blood plasma nitrite/nitrate levels in STZ animals after 4 and 8 weeks were increased by 44.6 and 61.9%, respectively. Ca2+-independent nitric oxide synthase activity in gastric fundus strips and stomach corpus mucosa from STZ rats after 4 weeks was markedly enhanced by 37.4 and 31.9%, respectively, suggesting an enhanced nitric oxide production. In vivo insulin treatment prevented diabetes-induced alterations in smooth muscle contractility. We conclude that the smooth muscle dysfunction evoked by experimental diabetes causing diminished contractions of fundus strips to carbachol and galanin is at least partly due to the increased nitric oxide synthesis.

Porcine galanin (1-29)-NH2, galantide (M15) and galanin (1-14)-(alpha-aminobutyric acid8)-scyliorhinin-I used in concentrations of 300, 1,000 and 3,000 nM respectively caused contractions of rat fundus strips. The contractile responses to galanin(1-29)-NH2 were not modified by atropine (10 microM), guanethidine (10 microM), naloxone (1 microM), a mixture of propranolol (10 microM) and phentolamine (10 microM), indomethacin (10 microM), a mixture of mepyramine (10 microM) and cimetidine (10 microM), saralasin (10 microM), and spantide (100 microM). The effects of M15 and galanin(1-14)-(alpha-aminobutyric acid8)-scyliorhinin-I were significantly decreased by atropine for 36 and 18% and by spantide for 37 and 26% respectively. Indomethacin inhibited the muscle response to M15 without influence on the galanin (1-14)-(alpha-aminobutyric acid8)-scyliorhinin-I-induced action. These results support findings that galanin (1-29)-NH2 contracts rat gastric fundus strips by stimulating specific receptors localized on the surface of smooth muscle cells. M15 and galanin(1-14)-(alpha-aminobutyric acid8)-scyliorhinin-I seem to contract smooth muscles not only by acting at galanin receptors, but by interacting with muscarinic or tachykinin receptors or modulating the release of acetylcholine and substance P. Diltiazem (EC50 825 nM), dantrolene (EC50 30.2 microM) and the phospholipase C inhibitors U-73122 (EC50 549 microM) and U-73343 (EC50 751 microM) lowered the contraction to galanin(1-29)-NH2 in a concentration-dependent manner. These observations imply that though the extracellular Ca2+ influx plays a major role in the action of galanin(1-29)-NH2, the release of Ca2+ ions from the intracellular stores contributes to the response of smooth muscles of galanin(1-29) NH2. Norepinephrine (30, 60, 100 and 300 nM) concentration-dependently reduced the Emax to galanin (1-29)-NH2 and reduced the slopes of the concentration-contraction curves, without a notable change in EC50. Pertussis toxin pre-treatment (10 and 30 mg/kg intravenous [i.v.]), 120 h before the experiment, notably increased the maximal response of the rat gastric fundus to galanin(1-29)-NH2, without a significant change in the properties of the concentration-contraction curves (EC50, slopes). The observations may suggest that pertussis toxin-sensitive GTP-binding proteins are involved in the modulation of the excitatory effects of galanin(1-29)-NH2 in the rat gastric fundus.

The study was undertaken to characterize the effects of the porcine galanin [pGal(1-29)-NH2] analogue [Lys14]pGal(1-15)-NH2 on rat gastric fundus. [Lys14]pGal(1-15)-NH2 is a less potent contractile agent than pGal(1-29)-NH2 (EC50 74.1 vs. 43.7 nmol/l, respectively) and shows a significantly lower maximal response than pGal(1-29)-NH2. Concentration-contraction curves were constructed for pGal(1-29)-NH2 alone (control) and pGal(1-29)-NH2 in the presence of 10, 100, and 1,000 nmol/l of [Lys14]pGal(1-15)-NH2. [Lys14]pGal(1-15)-NH2 shifted the concentration-contraction curves of pGal(1-29)-NH2 significantly to the right, whereas their linear portions remained parallel to that for the pGal(1-29)-NH2 control. [Lys14]pGal(1-15)-NH2 markedly increased the EC50 of the respective pGal(1-29)-NH2 concentration-contraction curves. It did not substantially change the maximal response of the muscles to pGal(1-29)-NH2 and the form of the respective concentration-contraction curves. Schild's plot gave a straight line with a slope of 0.84. The pA2 value for [Lys14]pGal(1-15)-NH2 was 8.23. [Lys14]pGal(1-15)-NH2 seems to be a partial Gal receptor agonist. Since the lack of specific Gal receptor antagonists in the gastrointestinal tract makes a precise characterization of its role as a motility modulator difficult, the position 14 in the pGal(1-29)-NH2 molecule looks as an attractive target in the search of a pure Gal receptor antagonist in the smooth muscles of the gut.

Tubulin partition between soluble and polymeric forms is tightly regulated in cells. Stathmin and tubulin tyrosine ligase (TTL)a each form stable complexes with tubulin and inhibit tubulin polymerization. Here we explore the mutual relationship between these proteins in vitro and demonstrate that full-length stathmin and TTL compete for binding to tubulin and fail to make a stable tubulin:stathmin:TTL triple complex in solution. Moreover, stathmin depresses TTL tubulin tyrosination activity in vitro. These results suggest that TTL and stathmin have either a partially overlapping footprint on the tubulin dimer or that stathmin induces a tubulin conformation incompatible with stable TTL binding.

Fluctuations in the number of colloid particles adsorbed irreversibly under diffusion and flow were determined. The experimental measurements were carried out in the impinging‐jet cells using as model colloids the monodisperse polystyrene latex particles of micrometer size range adsorbing at mica sheets. The surface concentration of adsorbed particles was determined quantitatively using the direct microscope observation method coupled with an image analyzing system. Two series of experiments were performed (i) for diffusion controlled adsorption when the random sequential adsorption (RSA) mechanism was valid and (ii) for flow controlled adsorption. It was found that in the case of RSA the reduced variance of the distributions decreased markedly for increasing surface concentration θ in accordance with theoretical predictions based on the mean‐field approximation. The experimental results were in a good agreement with the numerical simulations performed according to the RSA algorithm. It was also determine...

Localized, irreversible adsorption of interacting colloid particles from well-defined flows was studied experimentally and theoretically. The impinging-jet cells were used for creating the axisymmetric and plane-parallel (slot) laminar flows, enabling a direct microscope determination of particle adsorption kinetics. Monodisperse suspension of polystyrene latex particles was used for measuring the influence of flow intensity (shear rate) on particle adsorption kinetics. The experimental data were interpreted in terms of the approximate analytical predictions derived using the random sequential adsorption (RSA) approach valid for low and moderate surface concentrations. For an arbitrary range of surface concentrations the general sequential Brownian dynamics (SBD) simulation method was used to interpret the experimental data. It was found that these theoretical methods reflected well the characteristic features of the adsorption experiments, especially the significant decrease of adsorption kinetics for higher flow shear rates and low ionic strengths caused by the hydrodynamic scattering effect (HSE). Due to this effect, the surface-blocking phenomena for spherical particles become analogous to elongated nonspherical particles under no-flow adsorption conditions.

The kinetics of irreversible adsorption of colloid and larger particles from flowing suspensions onto solid—liquid interfaces was studied theoretically and experimentally. The controlled forced convection transport conditions were realized by using the new experimental cell based on the slot impinging jet principle. From the numerical solution of the Navier—Stokes equation it was shown that the cell area in the vicinity of the symmetry plane is uniformly accessible for particles. This property facilitated a quantitative interpretation of experimental results obtained using the direct microscope observation method and monodisperse model suspensions. The influence of the flow rate (Reynolds number), bulk suspension concentration, and the ionic strength on the adsorption rate (initial flux) was studied systematically. The experimental results were found to be in quantitative agreement with the convective mass-transfer theory, indicating that the new cell was a powerful tool for studying colloid particle interactions with interfaces.

The aim of this work was to develop a novel method of preparation of loaded nanosize capsules based on liquid core encapsulation by biocompatible polyelectrolyte (PE) multilayer adsorption, with or without pegylated outermost layer. Using AOT (docusate sodium salt) as emulsifier, we obtained cores, stabilized by an AOT/PLL (poly-L-lysine hydrobromide) surface complex. These positively charged cores were encapsulated by layer-by-layer adsorption of polyelectrolytes, biocompatible polyanion PGA (poly-L-glutamic acid sodium salt), and biocompatible polycation PLL. We used the saturation method for formation of consecutive layers, and we determined the optimal conditions concerning concentration of surfactant and polyelectrolytes to form stable shells. The average size of the obtained capsules was 60 nm. Pegylated external layer were prepared using PGA-g-PEG (PGA grafted by PEG poly(ethylene glycol)). The capsules were stable for at least a period of 3 months. These nanocapsules were biocompatible when tested for cytotoxicity in a cellular coculture assay and demonstrated no or very low nonspecific binding to peripheral blood mononuclear cells when tested by flow cytometry. In order to study drug effects on leukemia cells, beta-carotene and vitamin A have been encapsulated as model drugs.

The maximal responses (Emaxs) of isolated rat gastric fundus strips to 300 n m porcine galanin (Gal) were decreased in a concentration-dependent manner by terikalant (RP 62719). EC50of the agent equalled 4.39 μ m (2.35–8.22). On the contrary the action of 30 n m of carbachol were not affected by the modulator in concentrations up to 30 μ m . It is concluded that potassium currents may contribute to the modulation of Gal myotropic activity in the gut.

Microtubules are decorated with chemically diverse and evolutionarily conserved posttranslational modifications that mark them for specialized functions in cells. Other than viruses and clathrin cages, microtubules are the only known hollow polymers in eukaryotic cells. Acetylation on alpha-tubulin Lys40 stands out as the only known tubulin posttranslational modification located in the microtubule lumen. It marks stable, long-lived microtubules and is required for polarity establishment and directional migration. Tubulin acetyltransferase (TAT) presents a puzzle: its activity is stimulated by microtubules, yet the luminal location of Lys40 hinders its access. TAT was proposed to access its substrate by diffusing from microtubule ends, engaging the Lys40 loop from the exterior of the microtubule or gaining access through openings or defects in the microtubule. To elucidate substrate access by TAT and uncover the molecular basis for the in vivo correlation between acetylation and microtubule age, we combined X-ray crystallography, electron microscopy, biochemical and single-molecule fluorescence analyses, and modeling. We report the first crystal structure of TAT in complex with a bisubstrate analog that together with structure-based functional analyses constrains the active enzyme to the microtubule lumen and reveal the structural determinants for Lys40 loop recognition. Unexpectedly, acetylation by TAT proceeds stochastically along the microtubule without a preference for ends despite the luminal location of the acetylation site. Single-molecule fluorescence imaging reveals that TAT efficiently and stochastically scans the microtubule, while modeling and kinetic analyses demonstrate that TAT catalytic activity, rather than diffusion through the lumen, is rate-limiting. Consistent with this, our 1.35A X-ray complex crystal structure reveals that the TAT active site is suboptimal for supporting the proton transfer required for acetylation. Thus, by virtue of its preference for the microtubule and its low catalytic rate, TAT alone can function as an enzymatic timer for microtubule lifetimes.

Triggering receptor expressed on myeloid cells like transcript-1 (TLT-1) is an abundant platelet-specific, type I transmembrane receptor. The extracellular fragment of TLT-1 consists of a single, immunoglobulin-like domain connected to the platelet cell membrane by a linker region called the stalk. Here we present evidence that a soluble fragment of the TLT-1 extracellular domain is found in serum of humans and mice and that an isoform of similar mass is released from platelets following activation with thrombin. We also report the crystal structure of the immunoglobulin domain of TLT-1 determined at the resolution of 1.19 A. The structure of TLT-1 is similar to other immunoglobulin-like variable domains, particularly those of triggering receptor expressed on myeloid cells-1 (TREM-1), the natural killer cell-activating receptor NKp44, and the polymeric immunoglobulin receptor. Particularly interesting is a 17-amino acid segment of TLT-1, homologous to a fragment of murine TREM-1, which, in turn, showed activity in blocking the TREM-1-mediated inflammatory responses in mice. Structural similarity to TREM-1 and polymeric immunoglobulin receptor, and evidence for a naturally occurring soluble fragment of the TLT-1 extracellular domain, suggest that this immunoglobulin-like domain autonomously plays an as yet unidentified, functional role.

ClpP, the proteolytic component of the ATP-dependent ClpAP and ClpXP chaperone/protease complexes, has 14 identical subunits organized in two stacked heptameric rings. The active sites are in an interior aqueous chamber accessible through axial channels. We have determined a 1.9 A crystal structure of Escherichia coli ClpP with benzyloxycarbonyl-leucyltyrosine chloromethyl ketone (Z-LY-CMK) bound at each active site. The complex mimics a tetrahedral intermediate during peptide cleavage, with the inhibitor covalently linked to the active site residues, Ser97 and His122. Binding is further stabilized by six hydrogen bonds between backbone atoms of the peptide and ClpP as well as by hydrophobic binding of the phenolic ring of tyrosine in the S1 pocket. The peptide portion of Z-LY-CMK displaces three water molecules in the native enzyme resulting in little change in the conformation of the peptide binding groove. The heptameric rings of ClpP-CMK are slightly more compact than in native ClpP, but overall structural changes were minimal (rmsd approximately 0.5 A). The side chain of Ser97 is rotated approximately 90 degrees in forming the covalent adduct with Z-LY-CMK, indicating that rearrangement of the active site residues to a active configuration occurs upon substrate binding. The N-terminal peptide of ClpP-CMK is stabilized in a beta-hairpin conformation with the proximal N-terminal residues lining the axial channel and the loop extending beyond the apical surface of the heptameric ring. The lack of major substrate-induced conformational changes suggests that changes in ClpP structure needed to facilitate substrate entry or product release must be limited to rigid body motions affecting subunit packing or contacts between ClpP rings.

Methods of theoretical and experimental evaluation of irreversible adsorption of particles, e.g., colloids and globular proteins at heterogeneous surfaces were reviewed. The theoretical models were based on the generalized random sequential adsorption (RSA) approach. Within the scope of these models, localized adsorption of particles occurring as a result of short-ranged attractive interactions with discrete adsorption sites was analyzed. Monte-Carlo type simulations performed according to this model enabled one to determine the initial flux, adsorption kinetics, jamming coverage and the structure of the particle monolayer as a function of the site coverage and the particle/site size ratio, denoted by lambda. It was revealed that the initial flux increased significantly with the site coverage theta(s) and the lambda parameter. This behavior was quantitatively interpreted in terms of the scaled particle theory. It also was demonstrated that particle adsorption kinetics and the jamming coverage increased significantly, at fixed site coverage, when the lambda parameter increased. Practically, for alpha = lambda2theta(s)1 the jamming coverage at the heterogeneous surfaces attained the value pertinent to continuous surfaces. The results obtained prove unequivocally that spherically shaped sites were more efficient in binding particles in comparison with disk-shaped sites. It also was predicted that for particle size ratio lambda4 the site multiplicity effect plays a dominant role, affecting significantly the structure of particle monolayers and the jamming coverage. Experimental results validating main aspects of these theoretical predictions also have been reviewed. These results were derived by using monodisperse latex particles adsorbing on substrates produced by covering uniform surface by adsorption sites of a desired size, coverage and surface charge. Particle deposition occurred under diffusion-controlled transport conditions and their coverage was evaluated by direct particle counting using the optical and electron microscopy. Adsorption kinetics was quantitatively interpreted in terms of numerical solutions of the governing diffusion equation with the non-linear boundary condition derived from Monte-Carlo simulations. It was proven that for site coverage as low as a few percent the initial flux at heterogeneous surfaces attained the maximum value pertinent to homogeneous surfaces. It also was demonstrated that the structure of larger particle monolayers, characterized in terms of the pair correlation function, showed much more short-range ordering than predicted for homogeneous surface monolayers at the same coverage. The last part of this review was devoted to detection of polyelectrolyte multilayers on various substrates via particle deposition experiments.

Amino acid contributions to protein recognition of naturally modified RNAs are not understood. Circular dichroism spectra and predictive software suggested that peptide tF2 (S1ISPW5GFSGL10 LRWSY15), selected from a phage display library to bind the modified anticodon domain of yeast tRNAPhe (ASL), adopted a beta-sheet structure. Ala residues incorporated at positions Pro4 and Gly6, both predicted to be involved in a turn, did not alter the peptide binding affinity for the ASLPhe, although major changes in the peptide's CD spectra were observed. Substitutions at three positions Pro4, Gly6, and Gly9, the latter not predicted to be in a turn, reduced the peptide's binding affinity to 4% of that of the unsubstituted tF2 and strongly influenced the peptide's secondary structure. The results suggest that peptides with different conformations, but similar affinities, adopt the optimal binding conformation, indicative of a structurally adaptive model of binding in which the modified RNA serves as a scaffold.

Methylation of RNA and proteins is one of a broad spectrum of post-transcriptional/translational mechanisms of gene expression regulation. Its functional signification is only beginning to be understood. A sensitive capillary electrophoresis mobility shift assay (CEMSA) for qualitative study of the methylation effect on biomolecules interaction is presented. Two RNA-peptide systems were chosen for the study. The first one consists of a 17-nucleotide analogue (+27-+43) of the yeast tRNA(Phe) anticodon stem and loop domain (ASL(Phe)) containing three of the five naturally occurring modifications (2'-O-methylcytidine (Cm(32)), 2'-O-methylguanine (Gm(34)) and 5-methylcytidine (m(5)C(40))) (ASL(Phe)-Cm(32),Gm(34),m(5)C(40)) and a 15-amino-acid peptide (named t(F)2: Ser(1)-Ile-Ser-Pro-Trp(5)-Gly-Phe-Ser-Gly-Leu(10)-Leu- Arg-Trp-Ser-Tyr(15)) selected from a random phage display library (RPL). A peptide-concentration-dependent formation of an RNA-peptide complex was clearly observable by CEMSA. In the presence of the peptide the capillary electrophoresis (CE) peak for triply methylated ASL(Phe) shifted from 18.16 to 20.90 min. Formation of the complex was not observed when an unmethylated version of ASL(Phe) was used. The second system studied consisted of the (+18)-(+44) fragment of the trans-activation response element of human immunodeficiency virus type 1 (TAR RNA HIV-1) and a 9-amino-acid peptide of the trans-activator of transcription protein (Tat HIV-1) Tat(49-57)-NH(2) (named Tat1: Arg(49)-Lys-Lys-Arg(52)-Arg-Gln-Arg-Arg- Arg(57)-NH(2)). In the presence of Tat(49-57)-NH(2) a significant shift of migration time of TAR from 18.66 min to 20.12 min was observed. Methylation of a residue Arg(52)-->Arg(Me)(2), crucial for TAR binding, strongly disrupted formation of the complex. Only at a high micromolar peptide concentration a poorly shaped, broad peak of the complex was observed. CE was found to be an efficient and sensitive method for the analysis of methylation effects on interaction of biomolecules.

The study was undertaken to establish the pharmacological basis of the stimulatory activity of galantide (M15) and galanin(1-14)-(a-aminobutyric acid8-[Abu8])scyliorhinin-I [Scy-I] in gastric smooth muscle.Isotonic contractions of the isolated, longitudinal rat gastric fundus strips were recorded.Galanin, galanin(1-15)-NH2, M15 and galanin(1-14)-[Abu8]Scy-I elicited concentration-dependent contractions. Their EC50s equaled 12.95, 174, 70.06 and 187 nM respectively. Hill's coefficients for galanin and galanin(1-15)-NH2 were not different from unity, indicating an interaction of one peptide molecule with one receptor according to the principles of classical receptor theory. Hill's coefficients were 0.73 and 1.56 for M15 and galanin (1-14)-[Abu8]Scy-I, respectively, a value significantly different from unity. Cold-storage denervation, tetrodotoxin-TTX (1 mM), spantide (100 mM) and NK1-3 receptor antagonists SR140333, 48968, 142801 (up to 10 mM) notably diminished M15, galanin(1-14)-[Abu8]Scy-I, SP(5-11) and [Abu8]-Scy-I evoked contractions without affecting activities of galanin and galanin(1-15)-NH2. Additionally, cross-desensitization experiments attenuated activity of M15 and galanin(1-14)-[Abu8]Scy-I without any noticeable action on galanin or galanin(1-15)-NH2.The action of chimeric peptides on the smooth muscle of the rat gastrointestinal tract depended not only on the myogenic interaction of those peptides with galanin binding sites, but also on the activation of tachykinin receptors or the release of endogenous mediators from the presynaptic terminals.

Tubulin is subject to an abundant and diverse set of post-translational modifications that include phosphorylation, acetylation, poly-glutamylation, poly-glycylation and tyrosination. The highest density and variety of post-translational modifications are found in especially complex microtubule arrays like those of neurons or cilia. Not surprisingly, tubulin modification enzymes have been linked to human diseases including cancers and neurodegenerative disorders. I will present recent data from my lab on the mechanism of action of two tubulin modification enzymes that illustrate two divergent paradigms of tubulin recognition. Tubulin tyrosine ligase (TTL) adds a C-terminal Tyr to the exposed C-terminus of alpha-tubulin as part of a tyrosination/detyrosination cycle present in most eukaryotic cells. We solved the first crystal structure of tubulin tyrosine ligase that revealed how the TTL scaffold supported the expansion of the repertory of tubulin post-translational modification enzymes of the TTL like family that recognize either alpha- or beta-tubulin C-terminal tails. In addition to modifying tubulin, TTL also prevents tubulin from incorporating into microtubules by recognizing a tubulin dimer interface that would otherwise be involved in microtubule lattice interactions. I will also present recent work from my group on the structure and mechanism of action of tubulin acetyltransferase (TAT). TAT acetylates Lys-40 on alpha-tubulin in the microtubule lumen. We solved the 2.7Å structure of TAT bound to its ac-coA substrate as well as the 2.45Å structure of a catalytic inactive TAT mutant that reveals a domain swapped dimer in which the functionally essential N-terminus shows evidence of unprecedented structural plasticity. Implications for catalysis and microtubule stimulation of TAT activity will be discussed.

Microtubules are polymers essential for cell morphogenesis, cell division and intracellular transport. This polymer's basic building block is the α/β tubulin heterodimer, which associates head-to-tail and laterally to form the microtubule. Tubulin is subject to diverse, abundant and evolutionarily conserved post-translational modifications that mark subpopulations of microtubules. The highest density and variety of post-translational modifications are found in neurons or cilia. Not surprisingly, tubulin modification enzymes have been linked to human diseases including cancers and neurodegenerative disorders. We will present our recent work using a combination of X-ray crystallography, small angle X-ray scattering and functional assays to investigate the mechanism of tubulin tyrosine ligase (TTL). TTL catalyzes the ATP-dependent post-translational addition of a tyrosine to the C-terminal end of detyrosinated α-tubulin. The detyrosination/tyrosination cycle regulates recruitment of motors and proteins that track with the growing end of the microtubule. TTL function is essential for neuronal development and reduction in TTL levels is strongly associated with aggressive tumors resistant to chemotherapy. Our first X-ray crystal structure of TTL, defines the structural fold of the TTL-like family of tubulin-modifying enzymes. We show that TTL recognizes tubulin via a dual strategy: it engages the tubulin tail through low-affinity, high-specificity interactions through a conserved positively charged surface, and co-opts what is otherwise a homo-oligomerization interface in structurally related enzymes to form a tight hetero-oligomeric complex with tubulin. TTL forms an elongated complex with the tubulin dimer and prevents incorporation of the dimer into microtubules by capping the tubulin polymerization interface. Interestingly, TTL and stathmin, a ubiquitously expressed tubulin sequestering protein, compete for tubulin binding in vitro and stathmin inhibits tubulin tyrosination. These results suggest that TTL and stathmin have either a partially overlapping footprint on the tubulin dimer or that stathmin induces a tubulin conformation incompatible with stable TTL binding.

The contributions of the natural modified nucleosides to RNA identity in protein/RNA interactions are not understood. We had demonstrated that 15 amino acid long peptides could be selected from a random phage display library using the criterion of binding to a modified, rather than unmodified, anticodon domain of yeast tRNA(Phe) (ASL(Phe)). Affinity and specificity of the selected peptides for the modified ASL(Phe) have been characterized by fluorescence spectroscopy of the peptides' tryptophans. One of the peptides selected, peptide t(F)2, exhibited the highest specificity and most significant affinity for ASL(Phe) modified with 2'-O-methylated cytidine-32 and guanosine-34 (Cm(32) and Gm(34)) and 5-methylated cytidine-40 (m(5)C(40)) (K(d) = 1.3 +/- 0.4 microM) and a doubly modified ASL(Phe)-Gm(34),m(5)C(40) and native yeast tRNA(Phe) (K(d) congruent with 2.3 and 3.8 microM, respectively) in comparison to that for the unmodified ASL(Phe) (K(d) = 70.1 +/- 12.3 microM). Affinity was reduced when a modification altered the ASL loop structure, and binding was negated by modifications that disfavored hairpin formation. Peptide t(F)2's higher affinity for the ASL(Phe)-Cm(32),Gm(34),m(5)C(40) hairpin and fluorescence resonance energy transfer from its tryptophan to the hypermodified wybutosine-37 in the native tRNA(Phe) placed the peptide across the anticodon loop and onto the 3'-side of the stem. Inhibition of purified yeast phenylalanyl-tRNA synthetase (FRS) catalyzed aminoacylation of cognate yeast tRNA(Phe) corroborated the peptide's binding to the anticodon domain. The phage-selected peptide t(F)2 has three of the four amino acids crucial to G(34) recognition by the beta-structure of the anticodon-binding domain of Thermus thermophilus FRS and exhibited circular dichroism spectral properties characteristic of beta-structure. Thus, modifications as simple as methylations contribute identity elements that a selected peptide specifically recognizes in binding synthetic and native tRNA and in inhibiting tRNA aminoacylation.

The activity of short porcine galanin (Gal) analogues was tested in vitro using rat gastric fundus strips. The peptides contracted longitudinal smooth muscle in a concentration-dependent manner with the following order of potency: Gal(1–29) >[Cit 14 ]Gal(1– 15) >[Asp 14 ]Gal(1– 15) >[Dab 14 ]Gal(1– 15) >[Nle 14 ] Gal(1–15) >[Dpr 14 ]Gal(1– 15) >[Arg 14 ]Gal(1– 15) >[Orn 14 ]Gal(1– 15) >Gal(1–15). Only in the case of two peptides, namely [Cit 14 ]Gal(1–15) and [Dab 14 ]Gal(1–15) did the values of Hill coefficients, estimated from the appropriate concentration–contraction curves, differ significantly from unity. Our results indicate that both N- and C-terminals of Gal molecule contribute towards the affinity and activity of Gal in rat gastric smooth muscle cell receptors, indicating that their integrity is essential for its full excitatory myogenic action. The substitution of histidine with citruline, aspartic acid, norleucine or diaminobutyric acid in position 14 of the amino acid chain led to a considerable increase in potency, suggesting that amino acids located at this position might play a crucial role where the strength of short analogues is concerned.