The Experts below are selected from a list of 249 Experts worldwide ranked by ideXlab platform
Etana Padan - One of the best experts on this subject based on the ideXlab platform.
-
A pH-dependent conformational change of NhaA Na(+)/H(+) antiporter of Escherichia coli involves loop VIII-IX, plays a role in the pH response of the Protein, and is maintained by the Pure Protein in dodecyl maltoside.
The Journal of biological chemistry, 1999Co-Authors: Yoram Gerchman, Abraham Rimon, Etana PadanAbstract:Abstract Digestion with trypsin of purified His-tagged NhaA in a solution of dodecyl maltoside yields two fragments at alkaline pH but only one fragment at acidic pH. Determination of the amino acid sequence of the N terminus of the cleavage products show that the pH-sensitive cleavage site of NhaA, both in isolated everted membrane vesicles as well as in the Pure Protein in detergent, is Lys-249 in loop VIII–IX, which connects transmembrane segment VIII to IX. Interestingly, the two polypeptide products of the split antiporter remain complexed and co-purify on Ni2+-NTA column. Loop VIII–IX has also been found to play a role in the pH regulation of NhaA; three mutations introduced into the loop shift the pH profile of the Na+/H+ antiporter activity as measured in everted membrane vesicles. An insertion mutation introducing Ile-Glu-Gly between residues Lys-249 and Arg-250 (K249-IEG-R250) and Cys replacement of either Val-254 (V254C) or Glu-241 (E241C) cause acidic shift of the pH profile of the antiporter by 0.5, 1, and 0.3 pH units, respectively. Interestingly, the double mutant E241C/V254C introduces a basic shift of more than 1 pH unit with respect to the single mutation V254C. Taken together these results imply the involvement of loop VIII–IX in the pH-induced conformational change, which leads to activation of NhaA at alkaline pH.
-
a ph dependent conformational change of nhaa na h antiporter of escherichia coli involves loop viii ix plays a role in the ph response of the Protein and is maintained by the Pure Protein in dodecyl maltoside
Journal of Biological Chemistry, 1999Co-Authors: Yoram Gerchman, Abraham Rimon, Etana PadanAbstract:Abstract Digestion with trypsin of purified His-tagged NhaA in a solution of dodecyl maltoside yields two fragments at alkaline pH but only one fragment at acidic pH. Determination of the amino acid sequence of the N terminus of the cleavage products show that the pH-sensitive cleavage site of NhaA, both in isolated everted membrane vesicles as well as in the Pure Protein in detergent, is Lys-249 in loop VIII–IX, which connects transmembrane segment VIII to IX. Interestingly, the two polypeptide products of the split antiporter remain complexed and co-purify on Ni2+-NTA column. Loop VIII–IX has also been found to play a role in the pH regulation of NhaA; three mutations introduced into the loop shift the pH profile of the Na+/H+ antiporter activity as measured in everted membrane vesicles. An insertion mutation introducing Ile-Glu-Gly between residues Lys-249 and Arg-250 (K249-IEG-R250) and Cys replacement of either Val-254 (V254C) or Glu-241 (E241C) cause acidic shift of the pH profile of the antiporter by 0.5, 1, and 0.3 pH units, respectively. Interestingly, the double mutant E241C/V254C introduces a basic shift of more than 1 pH unit with respect to the single mutation V254C. Taken together these results imply the involvement of loop VIII–IX in the pH-induced conformational change, which leads to activation of NhaA at alkaline pH.
Reinhard Miller - One of the best experts on this subject based on the ideXlab platform.
-
Interfacial shear rheology of Protein–surfactant layers
Advances in Colloid and Interface Science, 2008Co-Authors: J Kragel, S R Derkatch, Reinhard MillerAbstract:The shear rheology of adsorbed or spread layers at air/liquid and liquid/liquid phase boundaries is relevant in a wide range of technical applications such as mass transfer, monolayers, foaming, emulsification, oil recovery, or high speed coating. Interfacial shear rheological properties can provide important information about interactions and molecular structure in the interfacial layer. A variety of measuring techniques have been proposed in the literature to measure interfacial shear rheological properties and have been applied to Pure Protein or mixed Protein adsorption layers at air/water or oil/water interfaces. Such systems play for example an important role as stabilizers in foams and emulsions. The aim of this contribution is to give a literature overview of interfacial shear rheological studies of Pure Protein and Protein/surfactant mixtures at liquid interfaces measured with different techniques. Techniques which utilize the damping of waves, spectroscopic or AFM techniques and all micro-rheological techniques will not discuss here.
-
Dynamic adsorption and characterization of phospholipid and mixed phospholipid/Protein layers at liquid/liquid interfaces
Advances in colloid and interface science, 2007Co-Authors: Yi Zhang, Reinhard Miller, Helmuth MöhwaldAbstract:Drop profile analysis tensiometry is applied to study the adsorption dynamics of phospholipids, Proteins and phospholipid/Protein mixtures at liquid/liquid interfaces. Measurements of the dynamic interfacial tension of phospholipid layers give information on the adsorption mechanism and the structure of the adsorption layer. The equilibrium and dynamic adsorption of Pure Protein solutions, i.e. human serum album (HSA), beta-lactoglobulin (beta-LG), beta-casein (beta-CA), can be explained well by the thermodynamic model of Frumkin and the diffusion-controlled adsorption theory. The adsorption behavior from mixed phospholipid/Protein solutions was also investigated in terms of dynamic interfacial tensions. Interestingly, a "skin-like" folded film of Pure Protein or phospholipid/Protein complex layers can be observed at curved surfaces at the water/oil interfaces. The addition of phospholipids accelerates the formation of the folded structure at the drop surface through co-adsorption of Proteins.
-
Comparative study of sensitivity and detection limit for the Protein bovine serum albumen using a new tensiograph assay against the standard UV-visible assay
European Workshop on Optical Fibre Sensors, 1998Co-Authors: N. D. Mcmillan, Daragh L. Dowling, M. O'neill, T. Yeomans, Reinhard MillerAbstract:A new multianalyser tensiograph approach to concentration measurements of Pure Protein solutions has been devised. Much work has been done over a long period using tensiometers and other surface analysis methods on Proteins, enzymes and complex surface active molecules.
Sanford A. Asher - One of the best experts on this subject based on the ideXlab platform.
-
Mechanisms by Which Organic Solvent Exchange Transforms Responsive Pure Protein Hydrogels into Responsive Organogels.
Biomacromolecules, 2020Co-Authors: Natasha Lynn Smith, Andrew E. Coukouma, Ryan S Jakubek, Sanford A. AsherAbstract:Responsive Pure Protein organogel sensors and catalysts are fabricated by replacing the aqueous mobile phase of Protein hydrogels with Pure ethylene glycol (EG). Exchanging water for EG causes irreversible volume phase transitions (VPT) in bovine serum albumin (BSA) polymers; however, BSA hydrogel and organogel sensors show similar volume responses to Protein-ligand binding. This work elucidates the mechanisms involved in this enabling irreversible VPT by examining the Protein secondary structure, hydration, and Protein polymer morphology. Organogel Proteins retain their native activity because their secondary structure and hydration shell are relatively unperturbed by the EG exchange. Conversely, the decreasing solvent quality initiates polymer phase separation to minimize the BSA polymer surface area exposed to EG, thus decreasing distances between BSA polymer strands. These Protein polymer morphology changes promote interProtein interactions between BSA polymer strands, which increase the effective polymer cross-link density and prevent organogel swelling as the mobile phase is exchanged back to water.
-
mechanisms by which organic solvent exchange transforms responsive Pure Protein hydrogels into responsive organogels
Biomacromolecules, 2020Co-Authors: Natasha Lynn Smith, Andrew E. Coukouma, Ryan S Jakubek, Sanford A. AsherAbstract:Responsive Pure Protein organogel sensors and catalysts are fabricated by replacing the aqueous mobile phase of Protein hydrogels with Pure ethylene glycol (EG). Exchanging water for EG causes irreversible volume phase transitions (VPT) in bovine serum albumin (BSA) polymers; however, BSA hydrogel and organogel sensors show similar volume responses to Protein–ligand binding. This work elucidates the mechanisms involved in this enabling irreversible VPT by examining the Protein secondary structure, hydration, and Protein polymer morphology. Organogel Proteins retain their native activity because their secondary structure and hydration shell are relatively unperturbed by the EG exchange. Conversely, the decreasing solvent quality initiates polymer phase separation to minimize the BSA polymer surface area exposed to EG, thus decreasing distances between BSA polymer strands. These Protein polymer morphology changes promote interProtein interactions between BSA polymer strands, which increase the effective pol...
-
Stimuli-Responsive Pure Protein Organogel Sensors and Biocatalytic Materials.
ACS applied materials & interfaces, 2019Co-Authors: Natasha Lynn Smith, Andrew E. Coukouma, David C. Wilson, Vincent Gray, Sanford A. AsherAbstract:Utilizing Protein chemistry in organic solvents has important biotechnology applications. Typically, organic solvents negatively impact Protein structure and function. Immobilizing Proteins via cross-links to a support matrix or to other Proteins is a common strategy to preserve the native Protein function. Recently, we developed methods to fabricate macroscopic responsive Pure Protein hydrogels by lightly cross-linking the Proteins with glutaraldehyde for chemical sensing and enzymatic catalysis applications. The water in the resulting Protein hydrogel can be exchanged for organic solvents. The resulting organogel contains Pure organic solvents as their mobile phases. The organogel Proteins retain much of their native Protein function, i.e., Protein-ligand binding and enzymatic activity. A stepwise ethylene glycol (EG) solvent exchange was performed to transform these hydrogels into organogels with a very low vapor pressure mobile phase. These responsive organogels are not limited by solvent/mobile phase evaporation. The solvent exchange to Pure EG is accompanied by a volume phase transition (VPT) that decreases the organogel volume compared to that of the hydrogel. Our organogel sensor systems utilize shifts in the particle spacing of an attached two-dimensional photonic crystal (2DPC) to report on the volume changes induced by Protein-ligand binding. Our 2DPC bovine serum albumin (BSA) organogels exhibit VPT that swell the organogels in response to the BSA binding of charged ligands like ibuprofen and fatty acids. To our knowledge, this is the first report of a Pure Protein organogel VPT induced by Protein-ligand binding. Catalytic Protein organogels were also fabricated that utilize the enzyme organophosphorus hydrolase (OPH) to hydrolyze toxic organophosphate (OP) nerve agents. Our OPH organogels retain significant enzymatic activity. The OPH organogel rate of OP hydrolysis is ∼160 times higher than that of un-cross-linked OPH monomers in a 1:1 ethylene glycol/water mixture.
J Kragel - One of the best experts on this subject based on the ideXlab platform.
-
interfacial shear rheology of Protein surfactant layers
Advances in Colloid and Interface Science, 2008Co-Authors: J Kragel, S R Derkatch, R MillerAbstract:The shear rheology of adsorbed or spread layers at air/liquid and liquid/liquid phase boundaries is relevant in a wide range of technical applications such as mass transfer, monolayers, foaming, emulsification, oil recovery, or high speed coating. Interfacial shear rheological properties can provide important information about interactions and molecular structure in the interfacial layer. A variety of measuring techniques have been proposed in the literature to measure interfacial shear rheological properties and have been applied to Pure Protein or mixed Protein adsorption layers at air/water or oil/water interfaces. Such systems play for example an important role as stabilizers in foams and emulsions. The aim of this contribution is to give a literature overview of interfacial shear rheological studies of Pure Protein and Protein/surfactant mixtures at liquid interfaces measured with different techniques. Techniques which utilize the damping of waves, spectroscopic or AFM techniques and all micro-rheological techniques will not discuss here.
-
Interfacial shear rheology of Protein–surfactant layers
Advances in Colloid and Interface Science, 2008Co-Authors: J Kragel, S R Derkatch, Reinhard MillerAbstract:The shear rheology of adsorbed or spread layers at air/liquid and liquid/liquid phase boundaries is relevant in a wide range of technical applications such as mass transfer, monolayers, foaming, emulsification, oil recovery, or high speed coating. Interfacial shear rheological properties can provide important information about interactions and molecular structure in the interfacial layer. A variety of measuring techniques have been proposed in the literature to measure interfacial shear rheological properties and have been applied to Pure Protein or mixed Protein adsorption layers at air/water or oil/water interfaces. Such systems play for example an important role as stabilizers in foams and emulsions. The aim of this contribution is to give a literature overview of interfacial shear rheological studies of Pure Protein and Protein/surfactant mixtures at liquid interfaces measured with different techniques. Techniques which utilize the damping of waves, spectroscopic or AFM techniques and all micro-rheological techniques will not discuss here.
Yoram Gerchman - One of the best experts on this subject based on the ideXlab platform.
-
A pH-dependent conformational change of NhaA Na(+)/H(+) antiporter of Escherichia coli involves loop VIII-IX, plays a role in the pH response of the Protein, and is maintained by the Pure Protein in dodecyl maltoside.
The Journal of biological chemistry, 1999Co-Authors: Yoram Gerchman, Abraham Rimon, Etana PadanAbstract:Abstract Digestion with trypsin of purified His-tagged NhaA in a solution of dodecyl maltoside yields two fragments at alkaline pH but only one fragment at acidic pH. Determination of the amino acid sequence of the N terminus of the cleavage products show that the pH-sensitive cleavage site of NhaA, both in isolated everted membrane vesicles as well as in the Pure Protein in detergent, is Lys-249 in loop VIII–IX, which connects transmembrane segment VIII to IX. Interestingly, the two polypeptide products of the split antiporter remain complexed and co-purify on Ni2+-NTA column. Loop VIII–IX has also been found to play a role in the pH regulation of NhaA; three mutations introduced into the loop shift the pH profile of the Na+/H+ antiporter activity as measured in everted membrane vesicles. An insertion mutation introducing Ile-Glu-Gly between residues Lys-249 and Arg-250 (K249-IEG-R250) and Cys replacement of either Val-254 (V254C) or Glu-241 (E241C) cause acidic shift of the pH profile of the antiporter by 0.5, 1, and 0.3 pH units, respectively. Interestingly, the double mutant E241C/V254C introduces a basic shift of more than 1 pH unit with respect to the single mutation V254C. Taken together these results imply the involvement of loop VIII–IX in the pH-induced conformational change, which leads to activation of NhaA at alkaline pH.
-
a ph dependent conformational change of nhaa na h antiporter of escherichia coli involves loop viii ix plays a role in the ph response of the Protein and is maintained by the Pure Protein in dodecyl maltoside
Journal of Biological Chemistry, 1999Co-Authors: Yoram Gerchman, Abraham Rimon, Etana PadanAbstract:Abstract Digestion with trypsin of purified His-tagged NhaA in a solution of dodecyl maltoside yields two fragments at alkaline pH but only one fragment at acidic pH. Determination of the amino acid sequence of the N terminus of the cleavage products show that the pH-sensitive cleavage site of NhaA, both in isolated everted membrane vesicles as well as in the Pure Protein in detergent, is Lys-249 in loop VIII–IX, which connects transmembrane segment VIII to IX. Interestingly, the two polypeptide products of the split antiporter remain complexed and co-purify on Ni2+-NTA column. Loop VIII–IX has also been found to play a role in the pH regulation of NhaA; three mutations introduced into the loop shift the pH profile of the Na+/H+ antiporter activity as measured in everted membrane vesicles. An insertion mutation introducing Ile-Glu-Gly between residues Lys-249 and Arg-250 (K249-IEG-R250) and Cys replacement of either Val-254 (V254C) or Glu-241 (E241C) cause acidic shift of the pH profile of the antiporter by 0.5, 1, and 0.3 pH units, respectively. Interestingly, the double mutant E241C/V254C introduces a basic shift of more than 1 pH unit with respect to the single mutation V254C. Taken together these results imply the involvement of loop VIII–IX in the pH-induced conformational change, which leads to activation of NhaA at alkaline pH.
