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At least 253 records · Page 14Linked to original sources
PubMed2026

Identification and characterization of a wet adhesive protein extracted from Dreissena bugensis, the freshwater quagga mussel.

Mechanisms of wet adhesion have evolved in several aquatic organisms over millions of years. Yet, the repertoire of synthetic biocompatible wet adhesive materials is still limited. The byssus is a well-studied proteinaceous bioadhesive structure utilized by several bivalves to support sessile lifestyles in turbulent conditions. The quagga mussel (Dreissena bugensis) is a freshwater byssate and a notorious invasive species in the Great Lakes region. To identify adhesive proteins in the quagga mussel byssus, we utilized quantitative proteomics and found several proteins enriched at the byssus-substrate interface. Among the identified proteins was the Dbfp7 protein family. Dbfp7 is a small, polymorphic, and mostly disordered protein that lacks significant amounts of 3,4-dihydroxyphenylalanine (DOPA), a modified amino acid found in several marine mussel byssal proteins. Atomic force microscopy nanomechanical mapping of Dbfp7 films demonstrates that this protein exhibits adhesive ability in aqueous conditions. While DOPA is critical for marine mussel adhesion, interfacial electrochemistry of freshwater adhesive plaques suggests that freshwater byssates circumvent catechol-based adhesion. The functional characterization of Dbfp7 as a freshwater mussel adhesive protein advances the understanding of fundamental requirements for biocompatible wet adhesion, a crucial step for the development of bioinspired wet adhesive materials, such as improved medical adhesives.

Animals↗
PubMed2005

Characterization of pore scale NAPL morphology in homogeneous sands as a function of grain size and NAPL dissolution.

In this study, we investigate pore scale morphology of nonaqueous phase liquids (NAPLs) trapped in different pore sizes using tracer techniques. Specific interfacial area and saturation of NAPL trapped in homogeneous sands were measured using the interfacial and partitioning tracer techniques. The observed NAPL-water interfacial areas increased in a log-linear fashion with decreasing sand grain size, but showed no clear trend with residual NAPL saturation formed in the various grain sizes. The measured values were used to calculate the NAPL morphology index, which characterizes the spatial NAPL distribution within the pore space. The NAPL morphology indices, increased exponentially with decreasing grain size, indicating that the NAPL becomes smaller, but more blobs. For a fixed grain size, the specific interfacial area and saturation of the NAPL were measured following changes caused by dissolution using alcohol. The observed interfacial areas showed a decrease linearly as a function of the NAPL saturation.

Adsorption↗
PubMed2007

Interface Fermi level pinning at contacts between PEDOT: PSS and molecular organic semiconductors.

Photoemission studies of interfaces between molecular organic semiconductors and the conducting polymer PEDOT:PSS [mixture of PEDOT (poly-3,4-ethylenedioxy-thiophene) and PSS (polystyrenesulfonate)] demonstrate that it is impossible to control the charge injection barriers at such contacts by either a systematic change of the work function of the conducting polymer or that of the organic semiconductor. Instead, these interfaces are, in all cases, characterized by a charge transfer across the interface and a resulting Fermi level pinning. Thus interfacial charge barriers do not explain observed changes in device parameters as a function of the work function of the polymer electrode.

Journal Article↗
PubMed2004

Effect of oil substitution in chiral microemulsion electrokinetic chromatography.

In a previous publication (Pascoe, R., Foley, J. P., Analyst 2002, 127, 710-714), a novel chiral microemulsion based on 1.0% w/v dodecoxycarbonylvaline (DDCV), 0.50% v/v ethyl acetate and 1.2% v/v 1-butanol, was shown to provide rapid enantiomeric separations of various pharmaceutical compounds. The two deficiencies noted with this method were that the peak shapes obtained were asymmetric and the efficiencies were lower than those previously obtained using DDCV micelles (Peterson, A. G., Ahuja, E. S., Foley, J. P., J. Chromatogr. B 1996, 683, 15-28). This study examines the use of three alternative low-interfacial-tension oils (methyl acetate, methyl propionate, and methyl formate), in combination with DDCV, to characterize their effect on the elution range, efficiency, resolution, and enantioselectivity of various pharmaceutical enantiomers. The oils were evaluated in both the same volume percentage and the same molar concentration as ethyl acetate in the original DDCV microemulsion system. Including ethyl acetate, a total of seven microemulsion systems were examined. For the compounds that were separated, average enantioselectivities ranged from 1.09 to 1.28, with corresponding efficiencies of 14,000-20,000. While some interesting differences were observed, ethyl acetate still proved to be the most advantageous in terms of enantioselectivity, resolution, and elution range.

Acetates↗
PubMed2006

Two novel presenilin 1 gene mutations connected with frontotemporal dementia-like clinical phenotype: genetic and bioinformatic assessment.

Mutations in the amyloid precursor protein (APP), presenilin 1 (PSEN1) and presenilin 2 (PSEN2) genes are associated with early-onset familial Alzheimer's disease (EOAD). There are several reports describing mutations in PSEN1 in cases with frontotemporal dementia (FTD). We identified two novel mutations in the PSEN1 gene: L226F and L424H. The first mutation was detected in a patient with a clinical diagnosis of FTD and a post-mortem diagnosis of AD. The second mutation is connected with a clinical phenotype of variant AD with strong FTD signs. In silico modeling revealed that the mutations, as well as mutations used for comparison (F177L and L424R), change the local structure, stability and/or properties of the transmembrane regions of the presenilin 1 protein (PS1). In contrast, a silent non-synonymous substitution F175S is eclipsed by external residues and has no influence on PS1 interfacial surface. We suggest that in silico analysis of PS1 substitutions can be used to characterize novel PSEN1 mutations, to discriminate between silent polymorphisms and a potential disease-causing mutation. We also propose that PSEN1 mutations should be considered in FTD patients with no MAPT mutations.

Adult↗
PubMed2006

Surfactant effects on alpha-factors in aeration systems.

Aeration in wastewater treatment processes accounts for the largest fraction of plant energy costs. Aeration systems function by shearing the surface (surface aerators) or releasing bubbles at the bottom of the tank (coarse- or fine-bubble aerators). Surfactant accumulation on gas-liquid interfaces reduces mass transfer rates, and this reduction in general is larger for fine-bubble aerators. This study evaluates mass transfer effects on the characterization and specification of aeration systems in clean and process water conditions. Tests at different interfacial turbulence regimes show higher gas transfer depression for lower turbulence regimes. Contamination effects can be offset at the expense of operating efficiency, which is characteristic of surface aerators and coarse-bubble diffusers. Results describe the variability of alpha-factors measured at small scale, due to uncontrolled energy density. Results are also reported in dimensionless empirical correlations describing mass transfer as a function of physiochemical and geometrical characteristics of the aeration process.

Air↗
PubMed2005

Can a fibrillar interface be stronger and tougher than a non-fibrillar one?

Elasticity analysis and finite element simulations are carried out to study the strength of an elastic fibrillar interface. The fibrils are assumed to be in perfect contact with a rigid substrate. The adhesive interaction between the fibrils and the substrate is modelled by the Dugdale-Barenblatt model (DB). The condition for a fibrillar interface to be stronger than a non-fibrillar one is obtained for two regimes: (i) small fibril or flaw insensitive regime; (ii) large fibril or flaw sensitive regime. The transition between the two regimes is characterized by a dimensionless parameter that incorporates the material constants of the elastic fibrils and interfacial properties. The condition for a fibrillar interface to be tougher is also given. Lateral collapse is found to be detrimental to the strength and toughness of a fibrillar interface.

Adhesiveness↗
PubMed2000

Interpretation of static and dynamic neutron and light scattering from microemulsion droplets: effects of shape fluctuations

The theory of static and dynamic scattering of neutrons and light on microemulsion droplets is developed. The droplets are modeled by double-layered fluid spheres immersed in another fluid. The surface layer of arbitrary thickness thermally fluctuates in the shape. The scattering functions are consistently calculated up to the second order of the fluctuations. The bulk fluids and the layer are characterized by different scattering length densities (or dielectric constants). Involving the Helfrich's concept of interfacial elasticity, the theory is applied for the description of small-angle neutron scattering (SANS), neutron spin echo (NSE), and dynamic light scattering (DLS) experiments on dilute microemulsions. From the fits to the experimental data the bending elasticity and the Gaussian modulus are extracted. Due to the corrected account for the fluctuations, their values differ markedly from those obtained in the original works. The theory well describes the SANS experiments. In the case of DLS, we had to assume the shell of the solvent molecules to be built of several layers. Previous theories were in a sharp disagreement with the NSE experiments. A better agreement with these experiments is obtained if the dissipation in the surface layer is included into the consideration. From the experiments, the viscosity of the layer is estimated for a concrete microemulsion system.

Journal Article↗
PubMed2006

Surfactant effects on alpha factors in full-scale wastewater aeration systems.

Aeration is an essential process in the majority of wastewater treatment processes, and accounts for the largest fraction of plant energy costs. Aeration systems can achieve wastewater oxygenation by shearing the surface (surface aerators) or releasing bubbles at the bottom of the tank (coarse- or fine-bubble aerators). Surfactants accumulate on gas-liquid interfaces and reduce mass transfer rates. This reduction in general is larger for fine-bubble aerators. This study was conducted to evaluate mass transfer effects on the characterization and specification of aeration systems in clean and process water conditions. Tests at different interfacial turbulence regimes were analysed, showing higher gas transfer depression for lower turbulence regimes. Higher turbulence regimes can offset contamination effects, at the expense of operating efficiency. This phenomenon is characteristic of surface aerators and coarse bubble diffusers and is here discussed. The results explain the variability of alpha factors measured at small scale, due to uncontrolled energy density. Results are also reported in dimensionless empirical correlations that describe mass transfer as a function of physiochemical and geometrical characteristics of the aeration process.

Bioreactors↗
PubMed2005

Effect of thermal treatment on interfacial properties of beta-lactoglobulin.

The changes in the secondary conformation and surface hydrophobicity of beta-lactoglobulin subjected to different thermal treatments were characterized at pH values of 7, 5.5 and 4 using circular dichroism (CD) and hydrophobic dye binding. Heating resulted in a decrease in alpha-helix content with a corresponding increase in random coil at all pH values, this change being more pronounced for small heating times. Heating also resulted in an increase in surface hydrophobicity as a result of partial denaturation, this increase being more pronounced at pH 4. Thermal treatment resulted in a shift of the spread monolayer isotherm at air-water interface to smaller area per molecule due to increased flexibility and more loop formation. Thermal treatment led to an increase in interfacial shear elasticity and viscosity of adsorbed beta-lactoglobulin layer at pH 5.5 and 7. Interfacial shear elasticity, shear viscosity, stability of beta-lactoglobulin stabilized emulsion and average coalescence time of a single droplet at a planar oil-water interface with adsorbed protein layer exhibited a maximum for protein subjected to 15 min heat treatment at pH 7. At pH 5.5, the interfacial shear rheological properties and average single drop coalescence time were maximum for 15 min heat treatment whereas emulsion stability was maximum for 5 min heat treatment. At pH 7, thermal treatment was found to enhance foam stability. Analysis of thin film drainage indicated that interfacial shear rheological properties do not influence thin film drainage.

Circular Dichroism↗
PubMed1998

Structure and activity of rat pancreatic lipase-related protein 2.

The pancreas expresses several members of the lipase gene family including pancreatic triglyceride lipase (PTL) and two homologous proteins, pancreatic lipase-related proteins 1 and 2 (PLRP1 and PLRP2). Despite their similar amino acid sequences, PTL, PLRP1, and PLRP2 differ in important kinetic properties. PLRP1 has no known activity. PTL and PLRP2 differ in substrate specificity, bile acid inhibition, colipase requirement, and interfacial activation. To begin understanding the structural explanations for these functional differences, we solved the crystal structure of rat (r)PLRP2 and further characterized its kinetic properties. The 1.8 A structure of rPLRP2, like the tertiary structure of human PTL, has a globular N-terminal domain and a beta-sandwich C-terminal domain. The lid domain occupied the closed position, suggesting that rPLRP2 should show interfacial activation. When we reexamined this issue with tripropionin as substrate, rPLRP2 exhibited interfacial activation. Because the active site topology of rPLRP2 resembled that of human PTL, we predicted and demonstrated that the lipase inhibitors E600 and tetrahydrolipstatin inhibit rPLRP2. Although PTL and rPLRP2 have similar active sites, rPLRP2 has a broader substrate specificity that we confirmed using a monolayer technique. With this assay, we showed for the first time that rPLRP2 prefers phosphatidylglycerol and ethanolamine over phosphatidylcholine. In summary, we confirmed and extended the observation that PLRP2 lipases have a broader substrate specificity than PTL, we demonstrated that PLRP2 lipases show interfacial activation, and we solved the first crystal structure of a PLRP2 lipase that contains a lid domain.

Amino Acid Sequence↗
PubMed2001

Characterization of soluble protein extracts from keratinized tissues: identification of ubiquitin universally distributed in hair, nail, and stratum corneum.

Partial protein extracts were prepared from hair, nail, and stratum corneum in the absence of urea and interfacial surfactant. Tricine-sodium dodecyl sulfate polyacrylamide gel electrophoreses of these extracts showed low-molecular weight protein-rich patterns apparently different from those of whole protein extracts, which mainly consist of keratin bands. Several protein bands characterized each keratinized tissue or its derived species. In addition, we identified a major band of approximately 7 kDa as ubiquitin, a ubiquitously distributed protein that mediates non-lysosomal protein degradation, through direct amino acid sequence analysis of the electro-blotted protein band. The partial extraction is useful for investigation of soluble proteins retained in the keratinized tissues.

Animals↗
PubMed2003

Pre-transmembrane sequence of Ebola glycoprotein. Interfacial hydrophobicity distribution and interaction with membranes.

The membrane-interacting domain that precedes the transmembrane anchor of Ebola glycoprotein has been characterized. This aromatic-rich region is predicted to bind the membrane interface adopting an alpha-helical structure. Peptides representing either the Ebola glycoprotein pre-transmembrane sequence, or a 'scrambled' control with a different hydrophobic-at-interface moment, have been studied. Insertion into lipid monolayers, changes in intrinsic fluorescence and in infrared spectra demonstrated that only the wild-type peptide bound the interface under equilibrium conditions and adopted an alpha-helical conformation. The presence of the raft-associated lipid sphingomyelin did not affect membrane insertion, but it stimulated highly the membrane-destabilizing capacity of the pre-transmembrane sequence. A parallel study of the effects of the viral sequence and of melittin suggests that Ebola glycoprotein pre-transmembrane sequence might target membranes inherently prone to destabilization by lytic peptides.

Amino Acid Sequence↗
PubMed1998

Interfacial and Rheological Characteristics of Maghemite Aqueous Suspensions.

The interfacial properties and rheological behavior of the maghemite/water system have been investigated in this work. It has been determined that the real pzc and iep values of maghemite immersed in aqueous solution, containing KNO3 as electrolyte, are very close to 6.6. It has also been shown that the triple-layer site-binding model likely describes the electrical double layer of the maghemite/water system. The parameters obtained from this model indicate that the mechanism responsible for charging involves complexation reactions and that the interfacial properties of aqueous suspensions containing maghemite are very similar to those containing magnetite. Finally, rheological characterization of three maghemite samples with different average particle size showed that the maximum yield stress, at a fixed solid concentration, decreases as the sample particle size decreases. This anomalous behavior is originated by the apparition of relaxation superparamagnetic phenomena as a consequence of the decrease in the sample particle size. Copyright 1998 Academic Press.

Journal Article↗
PubMed1992

Comparative biophysical study of adsorbed calf serum, fetal bovine serum and mussel adhesive protein films.

Varying concentrations of different sera and adhesive agents are routinely used to increase cellular attachment to substrata. The surface-chemical effects of some of these surface-altering materials have been examined using ellipsometry, contact angle analysis and multiple-attenuated internal reflection infrared (MAIR-IR) spectroscopy. Specifically, 15% fetal bovine serum (FBS), Ham's F-12 (containing 10% FBS + 1% penicillin/streptomycin), 10% calf serum and mussel adhesive protein (MAP) were allowed to adsorb on to similar and different surfaces and then compared. Each of these preparations is capable of altering the surface-chemical properties of substrata with varying resultant surface energies. It is therefore important to characterize serum in the proper concentrations on the substrata under consideration in order to understand the interfacial effects.

Adhesiveness↗
PubMed2006

Unraveling the importance of protein-protein interaction: application of a computational alanine-scanning mutagenesis to the study of the IgG1 streptococcal protein G (C2 fragment) complex.

Alanine-scanning mutagenesis of protein-protein interfacial residues is a very important process for rational drug design. In this study, we have used the improved MM-PBSA approach that combining molecular mechanics and continuum solvent permits one to calculate the free energy differences through alanine mutation. To identify the binding determinants of the complex formed between the IgG1 (immunoglobulin-binding protein G) and protein G, we have extended the experimental alanine scanning mutagenesis study to both proteins of this complex and, therefore, to all interfacial residues of this binding complex. As a result, we present new residues that can be characterized as warm spots and, therefore, are important for complex formation. We have further increased the understanding of the functionality of this improved computational alanine-scanning mutagenesis approach testing its sensitivity to a protein-protein complex with an interface made up of residues mainly polar. In this study, we also have improved the method for the detection of an important amino acid residue that frequently constitutes a hot spot--tryptophan.

Alanine↗
PubMed2004

Nonlocality and short-range wetting phenomena.

We propose a nonlocal interfacial model for 3D short-range wetting at planar and nonplanar walls. The model is characterized by a binding-potential functional depending only on the bulk Ornstein-Zernike correlation function, which arises from different classes of tubelike fluctuations that connect the interface and the substrate. The theory provides a physical explanation for the origin of the effective position-dependent stiffness and binding potential in approximate local theories and also obeys the necessary classical wedge covariance relationship between wetting and wedge filling. Renormalization group and computer simulation studies reveal the strong nonperturbative influence of nonlocality at critical wetting, throwing light on long-standing theoretical problems regarding the order of the phase transition.

Journal Article↗
PubMed2004

How oligomerization contributes to the thermostability of an archaeon protein. Protein L-isoaspartyl-O-methyltransferase from Sulfolobus tokodaii.

To study how oligomerization may contribute to the thermostability of archaeon proteins, we focused on a hexameric protein, protein L-isoaspartyl-O-methyltransferase from Sulfolobus tokodaii (StoPIMT). The crystal structure shows that StoPIMT has a distinctive hexameric structure composed of monomers consisting of two domains: an S-adenosylmethionine-dependent methyltransferase fold domain and a C-terminal alpha-helical domain. The hexameric structure includes three interfacial contact regions: major, minor, and coiled-coil. Several C-terminal deletion mutants were constructed and characterized. The hexameric structure and thermostability were retained when the C-terminal alpha-helical domain (Tyr(206)-Thr(231)) was deleted, suggesting that oligomerization via coiled-coil association using the C-terminal alpha-helical domains did not contribute critically to hexamerization or to the increased thermostability of the protein. Deletion of three additional residues located in the major contact region, Tyr(203)-Asp(204)-Asp(205), led to a significant decrease in hexamer stability and chemico/thermostability. Although replacement of Thr(146) and Asp(204), which form two hydrogen bonds in the interface in the major contact region, with Ala did not affect hexamer formation, these mutations led to a significant decrease in thermostability, suggesting that two residues in the major contact region make significant contributions to the increase in stability of the protein via hexamerization. These results suggest that cooperative hexamerization occurs via interactions of "hot spot" residues and that a couple of interfacial hot spot residues are responsible for enhancing thermostability via oligomerization.

Amino Acid Sequence↗