326 research outputs found
The structural response of Human Serum Albumin to oxidation.
No full textThe most abundant plasma protein, Human Serum Albumin (HSA), plays a key part in the body antioxidant defense against reactive species [1]. This study was aimed at correlating oxidant-induced chemical and structural effects on HSA and was performed thanks to the use of a multi-probe platform allowing for the simultaneous collection of small angle x-ray scattering (SAXS), UV-vis absorption spectra and fluorescence emission [2].
We demonstrated that, despite the chemical damage of the protein occurs since the very first addition of the potent oxidant sodium hypochlorite, its structure is fairly preserved up to relevant oxidative modification (oxidant/HSA molar ratio of 80). At stronger oxidation conditions a dose-dependent unfolding of HSA occurs in a critical range of oxidant/HSA molar ratio of 80-120 that is given by a progressive detachment of one of the protein end-domains (Figure 1). This conformational variation, which implies the loss of roughly one third of the alpha-helix and the increase of the protein negative charge (detected by means of complementary circular dichroism and zeta potential measurements), is highly reproducible and represents a further fundamental property of this widely studied protein. The ability to tolerate high level of oxidation in a folded or only partially unfolded state, together with the stability to aggregation, confer to albumin optimal feature as a biological buffer to local formation of oxidants
Time-dependent pH scanning of the acid-induced unfolding of Human Serum Albumin
No full textThe most abundant plasma protein, Human Serum Albumin (HSA), is known to undergo conformational transitions in acidic environment [1]. To avoid buffer effects and correlate global and local structural changes, we developed a continuous acidification method and simultaneously monitored the protein changes by both small-angle scattering (SAXS) and fluorescence [2], using a dedicated instrumental platform [3].
The progressive acidification, based on the hydrolysis of glucono--lactone from pH 7 to pH 2.5, highlighted a multi-step unfolding involving the putative F form (pH 4) and an extended and flexible conformation (pH < 3.5). The scattering profile of the F form was extracted by component analysis and further 3D modeled, suggesting the rearrangement of the three albumin domains in a more elongated conformation, with a partial unfolding of one of the outer domains at this intermediate stage.
To test the stabilizing effect of fatty acids [4], here palmitic acid, we compared the acid unfolding process of albumin with and without ligand. We found that when binding the ligand the native conformation was favored up to lower pH values.
Our approach solved the problem of realizing a continuous, homogeneous and tunable acidification with simultaneous characterization applicable to study processes triggered by a pH decrease
Structural response of human serum albumin to oxidation: bological buffer to local formation of hypochlorite
No full textThe most abundant plasma protein, human serum albumin (HSA), plays a key part in the body's antioxidant defense against reactive species. This study was aimed at correlating oxidant-induced chemical and structural effects on HSA. Despite the chemical modification induced by the oxidant hypochlorite, the native shape is preserved up to oxidant/HSA molar ratio <80, above which a structural transition occurs in the critical range 80-120. This conformational variation involves the drifting of one of the end-domains from the rest of the protein and corresponds to the loss of one-third of the alpha-helix and a net increase of the protein negative charge. The transition is highly reproducible suggesting that it represents a well-defined structural response typical of this multidomain protein. The ability to tolerate high levels of chemical modification in a folded or only partially unfolded state, as well as the stability to aggregation, provides albumin with optimal features as a biological buffer for the local formation of oxidants
Time-Dependent pH Scanning of the Acid-Induced Unfolding of Human Serum Albumin Reveals Stabilization of the Native Form by Palmitic Acid Binding
No full textThe most abundant plasma protein, human serum albumin (HSA), is known to undergo several conformational transitions in an acidic environment. To avoid buffer effects and correlate global and local structural changes, we developed a continuous acidification method and simultaneously monitored the protein changes by both small-angle scattering (SAXS) and fluorescence. The progressive acidification, based on the hydrolysis of glucono-δ-lactone from pH 7 to pH 2.5, highlighted a multistep unfolding involving the putative F form (pH 4) and an extended and flexible conformation (pH < 3.5). The scattering profile of the F form was extracted by component analysis and further 3D modeled. The effect of acid unfolding at this intermediate stage was assigned to the rearrangement of the three albumin domains drifting apart toward a more elongated conformation, with a partial unfolding of one of the outer domains. To test the stabilizing effect of fatty acids, here palmitic acid, we compared the acid unfolding process of albumin with and without ligand. We found that when binding the ligand, the native conformation was favored up to lower pH values. Our approach solved the problem of realizing a continuous, homogeneous, and tunable acidification with simultaneous characterization applicable to study processes triggered by a pH decrease
Interview with Cedric Boeckx
No full textCedric Boeckx is a Research Professor at the Catalan Institute for Advanced Studies (ICREA), and a member of the Center for Theoretical Linguistics at the Universitat Autònoma de Barcelona. Most recently he was an Associate Professor of Linguistics at Harvard University. He is the author and editor of various books on syntax, minimalism and language (from a biolinguistic perspective). He is also the founding co-editor, with Kleanthes K. Grohmann, of the Open Access journal Biolinguistics. The interview came to fruition after we had the idea of asking various linguists the following question: "What is the right place for linguistics?". At first, we were looking for short, straightforward answers. The question soon proved to be hard to approach that way, and Prof. Cedric Boeckx was kind enough to accept our invitation for a more thorough elaboration on the subject, under the "Interview" section of our journal, which he generously granted us on November 7th, 2011, at the Faculty of Letters of the University of Porto, a day before his "Introduction to Biolinguistics" workshop, also there, and for which we are also very thankful. This text is a virtually word-for-word transcription of the recorded 2-hour long interview, subject only to minor revisions by our editorial team and some comments by the interviewee. We hope that the final result is of interest to students, researchers and people alike
Cedric Dover, April 15, 1948
No full textPortrait of Cedric Dover. Written on recto: For Harold with every good wish, Cedric. Written on verso: The late Cedric Dover, Eurasian at one time on the faculty at Fisk University, and author of the famous book on Negro art, for which Harold Jackman furnished much of the material; Photograph by Carl Van Vechten; 101 Central Park West; Cannot be reproduced without permission; April 15, 1948
The effect of fatty acid binding in the acid isomerizations of albumin investigated with a continuous acidification method
No full textThe protein Human Serum Albumin (HSA) is known to undergo conformational transitions towards partially unfolded forms triggered by acidification below pH 4.5. The extent of Fatty Acids (FA) binding has been thought to have an impact on the conformational equilibrium between the native and acid forms and to be a possible explanation for the observation of more than one band in early electrophoretic migration experiments at pH 4. We compared the acid-induced unfolding processes of commercial FA-free HSA, commercial “fatted” HSA and FA-HSA complexes, prepared at FA:HSA molar ratios between 1 and 6 by simple mixing and equilibration. We used a method for continuous acidification based on the hydrolysis of glucono-δ-lactone from pH 7 to pH 2.5, and followed the average protein changes by the blue shift of the intrinsic fluorescence emission and by performing a small angle X-ray scattering analysis on selected samples. The method also allowed for continuous monitoring of the increase of turbidity and laser light scattering of the protein samples related to the release of the insoluble ligands with acidification. Our results showed that the presence of FA interacting with albumin, an aspect often neglected in biophysical studies, affects the conformational response of the protein to acidification, and slightly shifts the loss of the native shape from pH 4.2 to pH 3.6. This effect increased with the FA:HSA molar ratio so that with three molar equivalents a saturation was reached, in agreement with the number of high-affinity binding sites reported for the FA. These findings confirm that a non-uniform level of ligand binding in an albumin sample can be an explanation for the early-observed conformational heterogeneity at pH 4
CEDRIC J. POWELL
No full textCEDRIC J. POWELL
Inducted: 2010
Citation:
For exceptional scientific and organizational work in establishing the physical basis (and infrastructure) for electron spectroscopies of solids, especially as applied to quantitative surface analysis and surface standards
Tenure: 1962-2006
Birth: 1935; Perth, Australia
Education:
University of Western Australia, BS (Physics), 1956
University of Western Australia, PhD (Physics), 1962
Positions held:
Physicist, Atomic Physics and Optical Physics Divisions, Institute for Basic Standards, 1962-1978
Chief, Surface Science Division, Center for Chemical Physics, 1978-1991
Leader, Surface Spectroscopies and Thin Films Group, Surface and Microanalysis Science Division, 1991-1994
NIST Fellow, Surface and Microanalysis Science Division, 1994-2006
NIST Scientist Emeritus, Surface and Microanalysis Science Division, 2007-Present
Honors:
US Department of Commerce Silver Medal (1983) and Gold Medal (1986)Award of Merit, American Society for Testing and Materials (ASTM) (1988)
Riviere Prize, UK ESCA Users Group (1992)
Creation of Cedric Powell Award by ASTM Committee E-42 on Surface Analysis (1993)
Creation of Powell Prize by the Surface Analysis Society of Japan (1995)
Albert Nerken Award, American Vacuum Society (2001)
Technology Prize, International Union of Vacuum Science, Technique, and Applications (2007)
Memberships:
American Physical Society, American Vacuum Society, American Assn. for the Advancement of Science
ASTM Committee E-42 on Surface Analysis, chairman (1980-85)
Board of Trustees, Gordon Research Conferences (1982-88), chairman (1985-86)
Board of Directors, American Vacuum Society (1988-89)
ISO Technical Committee 201 on Surface Chemical Analysis, chairman (1992-98)
Publications:
Co-editor of 3 books, co-author of 5 NIST databases, and an author of more than 240 publications including:
Powell, C. J., “Contrasting Valence-Band Auger-Electron Spectra for Silver and Aluminum”, Phys. Rev. Letters 30, 1179 (1973)
Powell, C. J., “Attenuation Lengths of Low-energy Electrons in Solids”, Surface Science 44, 29 (1974)
Powell, C. J., “Cross Sections for Ionization of Inner-shell Electrons by Electrons”, Rev. Mod. Phys. 48, 33 (1976)
Powell, C. J. and Seah, M. P., “Precision, Accuracy, and Uncertainty in Quantitative Surface Analyses by Auger-Electron Spectroscopy and X-ray Photoelectron Spectroscopy”, J. Vac. Sci. Technol. A 8, 735 (1990)
Tanuma, S., Powell, C. J., and Penn, D. R., ""Calculations of Electron Inelastic Mean Free Paths. II. Data for 27 Elements over the 50-2000 eV Range,"" Surface and Interface Analysis 17, 911 (1991)
Powell, C. J. and Jablonski, A., “Evaluation of Measured and Calculated Electron Inelastic Mean Free Paths Near Solid Surfaces,” J. Phys. Chem. Ref. Data 28, 19 (1999
Inferring effective field observables from a discrete model
No full textAspin system on a lattice can usually be modeled at large scales by an effective quantum field theory. A key mathematical result relating the two descriptions is the quantum central limit theorem, which shows that certain spin observables satisfy an algebra of bosonic fields under certain conditions. Here, we show that these particular observables and conditions are the relevant ones for an observer with certain limited abilities to resolve spatial locations as well as spin values. This is shown by computing the asymptotic behaviour of a quantum Fisher information metric as function of the resolution parameters. The relevant observables characterise the state perturbations whose distinguishability does not decay too fast as a function of spatial or spin resolution.The author is grateful to Tobias Osborne for discussions leading to this work. This work was supported by the ERC grants QFTCMPS and SIQS, by the cluster of excellence EXC 201 Quantum Engineering and Space-Time Research, and by the research fund of Hanyang University (HY-2016-2237)
Fabrication and optimization of stable, optically transparent, and reusable ph-responsive silk membranes
No full textThe fabrication of silk-based membranes that are stable, optically transparent and reusable is yet to be achieved. To address this bottleneck we have developed a method to produce transparent chromogenic silk patches that are optically responsive to pH. The patches were produced by blending regenerated silk fibroin (RSF), Laponite RD (nano clay) and the organic dyes neutral red and Thionine acetate. The Laponite RD played a central role in the patch mechanical integrity and prevention of dye leaching. The process was optimized using a factorial design to maximize the patch response to pH by UV absorbance and fluorescence emission. New patches of the optimized protocol, made from solutions containing 125 µM neutral red or 250 µM of Thionine and 15 mg/mL silk, were further tested for operational stability over several cycles of pH altering. Stability, performance, and reusability were achieved over the tested cycles. The approach could be extended to other reporting molecules or enzymes able to bind to Laponite
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