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Hydrophobic Domains (hydrophobic + domain)
Selected AbstractsA role of the C-terminus of aquaporin 4 in its membrane expression in cultured astrocytesGENES TO CELLS, Issue 7 2002Ken-ichi Nakahama Background: Aquaporin 4 (AQP4) is a predominant water channel protein in mammalian brains, which is localized in the astrocyte plasma membrane. Membrane targeting of AQP4 is essential to perform its function. The mechanism(s) of membrane targeting is not clear in astrocytes. Results: We investigated the role of the C-terminus of AQP4 (short isoform) in its membrane targeting by an expression study of C-terminal mutants of AQP4 in cultured astrocytes. The deletion of 26 C-terminal residues of AQP4 (AQP4,276,301aa) results in the intracellular localization of the protein. However, smaller deletions than 21 C-terminal residues did not alter its plasma membrane localization. These results suggest that C-terminal residues between Val276 and Ile280 play an important role in the expression of AQP4 in the plasma membrane. However, the plasma membrane localization of the AQP4(A276AAAA280) mutant (alanine substitution of Val276 -Ile280 of AQP4) suggests that another signal for membrane targeting exists in the C-terminus of AQP4. The deletion or point mutations of the PDZ binding motif of the AQP4(A276AAAA280) mutant resulted in the intracellular localization of the proteins. These results suggest that the PDZ binding motif may also be involved in the membrane targeting of AQP4. Conclusions: We found that the C-terminal sequence of AQP4 contains two important signals for membrane expression of AQP4 in cultured astrocytes. One is a hydrophobic domain and the other is a PDZ binding motif that exists in the C-terminus. [source] Microphase separation behavior on the surfaces of poly(dimethylsiloxane)- block -poly(2,2,3,3,4,4,4-heptafluorobutyl methacrylate) diblock copolymer coatingsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2009Zheng-Hong Luo Abstract Microphase separation behavior on the surfaces of poly(dimethylsiloxane)- block -poly(2,2,3,3,4,4,4-heptafluorobutyl methacrylate) (PDMS- b -PHFBMA) diblock copolymer coatings was investigated. The PDMS- b -PHFBMA diblock copolymers were successfully synthesized via atom transfer radical polymerization (ATRP). The chemical structure of the copolymers was characterized by nuclear magnetic resonance and Fourier transform infrared spectroscopy. Surface composition was studied by X-ray photoelectron spectroscopy. Copolymer microstructure was investigated by atomic force microscopy. The microstructure observations show that well-organized phase-separated surfaces consist of hydrophobic domain from PDMS segments and more hydrophobic domain from PHFBMA segments in the copolymers. The increase in the PHFBMA content can strengthen the microphase separation behavior in the PDMS- b -PHFBMA diblock copolymers. And the increase in the annealing temperature can also strengthen the microphase separation behavior in the PDMS- b -PHFBMA diblock copolymers. Moreover, Flory-Huggins thermodynamic theory was preliminarily used to explain the microphase separation behavior in the PDMS- b -PHFBMA diblock copolymers.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Probing the interaction forces between hydrophobic peptides and supported lipid bilayers using AFMJOURNAL OF MOLECULAR RECOGNITION, Issue 6 2007Guillaume Andre Abstract Despite the vast body of literature that has accumulated on tilted peptides in the past decade, direct information on the forces that drive their interaction with lipid membranes is lacking. Here, we attempted to use atomic force microscopy (AFM) to explore the interaction forces between the Simian immunodeficiency virus peptide and phase-separated supported bilayers composed of various lipids, i.e. dipalmitoylphosphatidylcholine, dioleoylphosphatidylcholine, dioleoylphosphatidic acid and dipalmitoylphosphatidylethanolamine. Histidine-tagged peptides were attached onto AFM tips terminated with nitrilotriacetate and tri(ethylene glycol) groups, an approach expected to ensure optimal exposure of the C-terminal hydrophobic domain. Force,distance curves recorded between peptide-tips and the different bilayer domains always showed a long-range repulsion upon approach and a lack of adhesion upon retraction, in marked contrast with the hydrophobic nature of the peptide. To explain this unexpected behaviour, we suggest a mechanism in which lipids are pulled out from the bilayer due to strong interactions with the peptide-tip, in agreement with the very low force needed to extract lipids from supported bilayers. Copyright © 2007 John Wiley & Sons, Ltd. [source] Neurotoxic species in prion disease: a role for PrP isoforms?JOURNAL OF NEUROCHEMISTRY, Issue 5 2007Christopher F. Harrison Abstract Prion diseases such as bovine spongiform encephalopathy in cattle and Creutzfeldt,Jakob disease in humans are associated with the misfolding and accumulation of an abnormal conformation of the host-encoded prion protein (PrP). Despite intensive research efforts conducted on PrP, the toxic agent involved in neurodegeneration is as yet unidentified. Several potential candidates have been proposed, each of which may be relevant to subsets of the broad array of prion diseases. In this study, we review current knowledge on neurotoxic PrP species, including the importance of a central hydrophobic domain for mediating neurotoxicty. [source] RNA-dependent RNA polymerase activity encoded by GB virus-B non-structural protein 5BJOURNAL OF VIRAL HEPATITIS, Issue 5 2000Zhong Phylogenetic analysis and polyprotein organization comparison have shown that GB virus-B (GBV-B) is closely related to hepatitis C virus (HCV). In this study, the coding region for GBV-B non-structural protein 5B (NS5B) was isolated by reverse transcription,polymerase chain reaction (RT,PCR) from pooled serum of GBV-B-infected tamarins. Expression of soluble GBV-B NS5B protein in Escherichia coli was achieved by removal of a 19-amino acid hydrophobic domain at the C-terminus of the protein. The truncated GBV-B NS5B (NS5B,CT19) was purified to homogeneity and shown to possess an RNA-dependent RNA polymerase (RdRp) activity in both gel-based and scintillation proximity assays. NS5B,CT19 required the divalent cation Mn2+ for enzymatic activity, at an optimal concentration of 15 m M. Interestingly, Mg2+, at concentrations up to 20 m M, did not support the GBV-B NS5B activity. This differs from HCV NS5B where both Mn2+ and Mg2+ can support RdRp activity. Zn2+ was found to inhibit the activity of GBV-B NS5B, with a 50% inhibitory concentration (IC50) of 5,10 ,M. Higher concentrations of monovalent salts (NaCl or KCl > 100 m M) and glycerol (> 3%) were also inhibitory. NS5B,CT19 was able to bind to RNA homopolymers, but utilized most efficiently poly(C), the one with the lowest binding affinity for RNA synthesis. Mutational analysis of GBV-B NS5B demonstrated the importance of several conserved sequence motifs for enzymatic activity. Based on sequence homology (, 37% identity and 52% similarity) between GBV-B and HCV NS5B proteins, the active GBV-B RdRp provides a good surrogate assay system for HCV polymerase studies. [source] Topological analysis and role of the transmembrane domain in polar targeting of PilS, a Pseudomonas aeruginosa sensor kinaseMOLECULAR MICROBIOLOGY, Issue 4 2000Julie Ethier In Pseudomonas aeruginosa, synthesis of pilin, the major protein subunit of the pili, is regulated by a two-component signal transduction system in which PilS is the sensor kinase. PilS is an inner membrane protein found at the poles of the bacterial cell. It is composed of three domains: an N-terminal hydrophobic domain; a central cytoplasmic linker region; and the C-terminal transmitter region conserved among other sensor kinases. The signal that activates PilS and, consequently, pilin transcription remains unknown. The membrane topology of the hydrophobic domain was determined using the lacZ and phoA gene fusion approach. In this report, we describe a topological model for PilS in which the hydrophobic domain forms six transmembrane helices, whereas the N- and C-termini are cytoplasmic. This topology is very stable, and the cytoplasmic C-terminus cannot cross the inner membrane. We also show that two of the six transmembrane segments are sufficient for membrane anchoring and polar localization of PilS. [source] Influence of N-Terminal Hydrophobicity of Cationic Peptides on Thermodynamics of their Interaction with Plasmid DNACHEMICAL BIOLOGY & DRUG DESIGN, Issue 5 2009Geetha N. Goparaju There is a need to understand the thermodynamics of interaction of cationic peptides with DNA to design better peptide based non-viral gene delivery vectors. The main aim of this study was to understand the influence of N-terminal hydrophobicity of cationic amphiphilic peptides on thermodynamics of interaction with plasmid DNA. The model peptides used were TATPTD and TATPTDs modified at the N-terminal with hydrophobic amino acids. The thermodynamic binding data from isothermal titration calorimetry were compared with ethidium bromide analysis and ultrafiltration to correlate the binding parameters with the structural features of the various peptides used. It was observed that peptides having a smaller hydrophobic domain at the N-terminal have good DNA condensing ability compared with the ones with a longer hydrophobic domain. Calorimetry of peptides that reached saturation binding indicated that enthalpy and entropy are favorable for the interaction. Moreover, the interaction of these peptides with DNA appears to be predominantly electrostatic. [source] Nanostructured copolymer gels for dsDNA separation by CEELECTROPHORESIS, Issue 23 2008Fen Wan Abstract Pluronics are triblock copolymers of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) that are able to form many different ordered nanostructures at appropriate polymer concentrations and temperatures in selective solvents. These nanostructured "gels" showed desirable criteria when used as DNA separation media, especially in microchip electrophoresis, including dynamic coating and viscosity switching. A ternary system of F127 (E99P69E99)/TBE buffer/1-butanol was selected as a model system to test the sieving performance of different nanostructures in separating dsDNA by CE. The nanostructures and their lattice constants were determined by small-angle X-ray scattering. Viscosity measurements showed the sol,gel transition phenomena. In addition to the cubic structure, successful electrophoretic separation of dsDNA in 2-D hexagonally packed cylinders was achieved. Results showed that without further optimization, ,X174 DNA,Hae III digest was well separated within 15,min in a 7-cm separation channel, by using F127/TBE/1-butanol gel with a 2-D hexagonal structure. A mechanism for DNA separations by those gels with both hydrophilic and hydrophobic domains is discussed. [source] Synthetic Hydrophilic Materials with Tunable Strength and a Range of Hydrophobic Interactions,ADVANCED FUNCTIONAL MATERIALS, Issue 14 2010Olha Hoy Abstract The ability to vary, adjust, and control hydrophobic interactions is crucial in manipulating interactions between biological objects and the surface of synthetic materials in aqueous environment. To this end a grafted polymer layer (multi-component mixed polymer brush) is synthesized that is capable of reversibly exposing nanometer-sized hydrophobic fragments at its hydrophilic surface and of tuning, turning on, and turning off the hydrophobic interactions. The reversible switching occurs in response to changes in the environment and alters the strength and range of attractive interactions between the layer and hydrophobic or amphiphilic probes in water. The grafted layer retains its overall hydrophilicity, while local hydrophobic forces enable the grafted layer to sense and attract the hydrophobic domains of protein molecules dissolved in the aqueous environment. The hydrophobic interactions between the material and a hydrophobic probe are investigated using atomic force microscopy measurements and a long-range attractive and contact-adhesive interaction between the material and the probe is observed, which is controlled by environmental conditions. Switching of the layer exterior is also confirmed via protein adsorption measurements. [source] Pseudobilayer Vesicle Formation via Layer-by-Layer Assembly of Hydrophobically Modified Polymers on Sacrificial Substrates,ADVANCED FUNCTIONAL MATERIALS, Issue 7 2005J. Khopade Abstract A bilayer of a hydrophobically modified polyelectrolyte, octadecyl poly(acrylamide) (PAAm), sandwiched between the layers of a hydrophilic polyelectrolyte, poly(ethyleneimine) (PEI), is prepared by the sequential electrostatic,hydrophobic,electrostatic-interaction-driven self-assembly on planar and colloid substrates. This process results in a PEI/[PAAm]2/PEI-multilayer-coated substrate. The removal of a PAA/PEI/[PAAm]2/PEI-multilayer-coated decomposable colloidal template produces hollow capsules. Irregular hydrophobic domains of the [PAAm]2 bilayer in the PEI/[PAAm]2/PEI-multilayer capsule are infiltrated with a lipid to obtain a uniform, distinct hydrophobic layer, imparting the capsule with a pseudobilayer vesicle structure. [source] PREPARATION AND CHARACTERIZATION OF MODIFIED WHEAT GLUTEN BY ENZYMATIC HYDROLYSIS-ULTRAFILTRATIONJOURNAL OF FOOD BIOCHEMISTRY, Issue 3 2008JIN-SHUI WANG ABSTRACT The present work was aimed to investigate the characteristics of the modified wheat gluten by enzymatic hydrolysis followed ultrafiltration membrane fractionation. An 8% aqueous dispersion of wheat gluten was hydrolyzed by papain, and then subjected to ultrafiltration membrane for fractionation. The molecular mass of the peptides released during enzymatic hydrolysis of gluten was in the range of 5,000,15,000 D according to gel permeation chromatography profiles. The resultant hydrolysate (retentate fraction) after membrane fractionation produced the desired products with a protein yield of about 89%. The modified glutens had higher surface hydrophobicity compared with the original gluten. Moreover, the modified gluten protein had superior solubility to the original gluten in pH 3,10. The enhanced foaming capacity in the pH ranges studied had been found in the modified gluten. The improved functional properties of the modified gluten were related to the well-balanced distribution of hydrophilic and hydrophobic domains. The modified gluten was rich in glutamic acid and proline. PRACTICAL APPLICATIONS Gluten is an economically important byproduct during processing of wheat starch. The expanded utilization of gluten in food and nonfood applications had been limited for lack of desirable functional properties. To extend the range of available functional properties it needs to be investigated further. The limited enzymatic hydrolysis and membrane ultrafiltration had been extensively studied and had been shown to be very effective for improving the functional properties of the proteins. In this present study, wheat gluten was modified by enzymatic hydrolysis , membrane ultrafiltration fractionation. This method was proved to be an efficient way to modify wheat gluten protein. The functional properties of the modified glutens were significantly improved compared to the original gluten. It is expected that the modified gluten with enhanced functional properties could be used in a wide range of foods as new components to enhance their nutritional value and functional properties in food processing. [source] Functional colloidal particles stabilized by layered silicate with hydrophilic face and hydrophobic polymer brushesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2009Yani Wu Abstract In this study, we describe a new strategy for producing narrowly dispersed functional colloidal particles stabilized by a nanocomposite with hydrophilic clay faces and hydrophobic polystyrene (PS) brushes on the edges. This method involves preparation of polymer brushes on the edges of clay layers and Pickering suspension polymerization of styrene in the presence of the nanocomposites. PS brushes on the edges of clay layers were prepared by atom transfer radical polymerization. X-ray diffraction and thermogravimetric analysis results indicated that PS chains were grafted to the edges of clay platelets. Transmission electron microscope results showed that different morphologies of clay-PS particles could be obtained in different solvents. In water, clay-PS particles aggregated together, in which PS chains collapsed forming nanosized hydrophobic domains and hydrophilic clay faces stayed in aqueous phase. In toluene, clay-PS particles formed face-to-face structure. Narrowly dispersed PS colloidal particles stabilized by clay-PS were prepared by suspension polymerization. Because of the negatively charged clay particles on the surface, the zeta potential of the PS colloidal particles was negative. Positively charged poly(2-vinyl pyridine) (P2VP) chains were adsorbed to the surface of PS colloidal particles in aqueous solution at a low pH value, and gold nanoparticles were prepared in P2VP brushes. Such colloidal particles may find important applications in a variety of fields including waterborne adhesives, paints, catalysis of chemical reactions, and protein separation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1535,1543, 2009 [source] Synthesis and characterization of proton-conducting copolyimides bearing pendant sulfonic acid groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2005Yan Yin Abstract A series of sulfonated copolyimides (co-SPIs) bearing pendant sulfonic acid groups were synthesized from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), bis(3-sulfopropoxy) benzidines (BSPBs), and common nonsulfonated diamines via statistical or sequenced polycondensation reactions. Membranes were prepared by casting their m -cresol solutions. The co-SPI membrane had a microphase-separated structure composed of hydrophilic and hydrophobic domains, but the connecting behavior of hydrophilic domains was different from that of the homo-SPIs. The co-SPI membranes displayed clear anisotropic membrane swelling in water with negligibly small dimensional changes in the plane direction of the membrane. With water uptake values of 39,94 wt %, they showed dimensional changes in membrane thickness of about 0.11,0.58, which were much lower than those of homo-SPIs. The proton conductivity , values of co-SPI membranes with ion exchange capacity values ranging from 1.95,2.32 meq/g increased sigmoidally with increasing relative humidity. They displayed , values of 0.05,0.16 S/cm at 50 °C in liquid water. Increasing temperature up to 120 °C resulted in further increase in proton conductivity. The co-SPI membranes showed relatively good conductivity stability during the aging treatment in water at 100 °C for 300 h. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1545,1553, 2005 [source] Synthesis and Characterization of Chiral [3,22]-IonenesMACROMOLECULAR SYMPOSIA, Issue 1 2005Reinaldo C. Bazito Abstract Summary: Two [3,22]-ionenes with pendent chiral groups, glucopyranosyl-[3,22]-ionene and ,-cyclodextrin-[3,22]-ionene, were synthesized by the reaction between the tosyl derivatives of the carbohydrate (methyl alpha-glucopyranoside or beta-cyclodextrin) and the tertiary [3,22]-polyamine obtained by selective demethylation of [3,22]-ionene. The derivatives were characterized by 1H NMR spectroscopy, presenting degrees of substitution of 30 and 45% for the glucosyl and cyclodextrin derivatives, respectively. It was shown by using pyrene as the fluorescent probe, that both polymers form hydrophobic domains, characteristic of micelle-mimetic polysoaps in aqueous solution. [source] Synthesis of poly(cystine bisamide)-PEG block copolymers grafted with 1-(3-aminopropyl)imidazole and their phase transition behaviorsPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 11 2008Byung Suk Jin Abstract New biodegradable and pH-sensitive block copolymers were prepared by grafting 1-(3-aminopropyl) imidazole onto a backbone polymer formed via condensation polymerization between l -cystine and EDTA-dianhydride. The copolymer with a graft ratio of 79% exhibited a good buffering capacity and pH sensitivity. These are attributed to protonation,deprotonation of the imidazole ring at around pH 7. The copolymers with less imidazole content did not show any apparent responses to changes in pH. The particle size of the copolymer aggregate formed under basic conditions was around 200,nm and increased with decreasing pH. The critical aggregation values at pH 6.0 and 8.0, derived from the changes of intensity ratios (I1/I3) in the emission spectrums of pyrene, were approximately 0.17 and 0.05,mg/ml, respectively. The surface charge of the aggregates increased with the decreasing pH as a result of the increase in protonation of imidazole and the tertiary amine in the polymer chain. The microviscosity of hydrophobic domains was estimated using 1,6-diphenyl-1,3,5-hexatriene. The decrease of the anisotropy value under acidic conditions reflects a disruption of hydrophobic interaction. Copyright © 2008 John Wiley & Sons, Ltd. [source] Identification and Functional Characterization of the Delta 6-Fatty Acid Desaturase Gene from Thamnidium elegansTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 1 2007DEPEI WANG ABSTRACT. A cDNA sequence was cloned from the filamentous fungus Thamnidium elegans As3.2806 using reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends method (RACE). Sequence analysis indicated that this cDNA sequence has an open reading frame of 1,380 bp, which encodes a 52.4 kDa peptide of 459 amino acids. The designated amino acid sequence has high similarity with that found in fungal delta 6-fatty acid desaturases: it shows three conserved histidine-rich motifs and two hydrophobic domains. A cytochrome b5-like domain was observed at the N-terminus. To elucidate the function of this novel putative desaturase, the open reading frame was cloned into the intracellular expression vector pPIC3.5K and the gene was expressed heterologously in Pichia pastoris. Accumulation of ,-linolenic acid to the level of 6.83% in total fatty acid demonstrated that the deduced amino acid sequence possesses of delta 6-fatty acid desaturase activity. [source] Recombinant human elastin polypeptides self-assemble into biomaterials with elastin-like propertiesBIOPOLYMERS, Issue 4 2003Catherine M. Bellingham Abstract Processes involving self-assembly of monomeric units into organized polymeric arrays are currently the subject of much attention, particularly in the areas of nanotechnology and biomaterials. One biological example of a protein polymer with potential for self-organization is elastin. Elastin is the extracellular matrix protein that imparts the properties of extensibility and elastic recoil to large arteries, lung parenchyma, and other tissues. Tropoelastin, the ,70 kDa soluble monomeric form of elastin, is highly nonpolar in character, consisting essentially of 34 alternating hydrophobic and crosslinking domains. Crosslinking domains contain the lysine residues destined to form the covalent intermolecular crosslinks that stabilize the polymer. We and others have suggested that the hydrophobic domains are sites of interactions that contribute to juxtaposition of lysine residues in preparation for crosslink formation. Here, using recombinant polypeptides based on sequences in human elastin, we demonstrate that as few as three hydrophobic domains flanking two crosslinking domains are sufficient to support a self-assembly process that aligns lysines for zero-length crosslinking, resulting in formation of the crosslinks of native elastin. This process allows fabrication of a polymeric matrix with solubility and mechanical properties similar to those of native elastin. © 2003 Wiley Periodicals, Inc. Biopolymers 70: 445,455, 2003 [source] Influence of the hydrophilic face on the folding ability and stability of ,-helix bundles: relevance to the peptide catalytic activityCHEMICAL BIOLOGY & DRUG DESIGN, Issue 3 2000S.E. Blondelle Although not the sole feature responsible, the packing of amino acid side chains in the interior of proteins is known to contribute to protein conformational specificity. While a number of amphipathic peptide sequences with optimized hydrophobic domains has been designed to fold into a desired aggregation state, the contribution of the amino acids located on the hydrophilic side of such peptides to the final packing has not been investigated thoroughly. A set of self-aggregating 18-mer peptides designed previously to adopt a high level of ,-helical conformation in benign buffer is used here to evaluate the effect of the nature of the amino acids located on the hydrophilic face on the packing of a four ,-helical bundle. These peptides differ from one another by only one to four amino acid mutations on the hydrophilic face of the helix and share the same hydrophobic core. The secondary and tertiary structures in the presence or absence of denaturants were determined by circular dichroism in the far- and near-UV regions, fluorescence and nuclear magnetic resonance spectroscopy. Significant differences in folding ability, as well as chemical and thermal stabilities, were found between the peptides studied. In particular, surface salt bridges may form which would increase both the stability and extent of the tertiary structure of the peptides. The structural behavior of the peptides may be related to their ability to catalyze the decarboxylation of oxaloacetate, with peptides that have a well-defined tertiary structure acting as true catalysts. [source] | ||||||||||||||||