Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Protein Denaturation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources
PubMed1983

A critical role of lysine residues in the stimulation of tissue plasminogen activator by denatured proteins and fibrin clots.

Two-chain 70 000-dalton plasminogen activator of tissue origin displays only weak activity toward plasminogen in a two-component system. The rate of activation is enhanced a minimum of 50-fold by the presence of fibrin clots or denatured proteins. The stimulation must depend on both chemical determinants and spatial configuration, since native proteins, including fibrinogen, lack significant stimulatory activity. These studies employed chemical modifications of four stimulatory proteins (fibrin, denatured fibrinogen, denatured IgG and denatured ovalbumin) to identify a critical role for lysine residues. Arginine, aspartic acid, cysteine, cystine, glutamic acid, histidine, methionine, tyrosine and tryptophan were found not to be essential. The critical spatial determinant(s) remain(s) unknown.

Animals↗
PubMed2003

Specific interaction between GroEL and denatured protein measured by compression-free force spectroscopy.

We investigated the interaction between GroEL and a denatured protein from a mechanical point of view using an atomic force microscope. Pepsin was bound to an atomic force microscope probe and used at a neutral pH as an example of denatured proteins. To measure a specific and delicate interaction force, we obtained force curves without pressing the probe onto GroEL molecules spread on a mica surface. Approximately 40 pN of tensile force was observed for approximately 10 nm while pepsin was pulled away from the chaperonin after a brief contact. This length of force duration corresponding to the circumference of GroEL's interior cavity was shortened by the addition of ATP. The relation between the observed mechanical parameters and the chaperonin's refolding function is discussed.

Adenosine Triphosphate↗
PubMed1999

The solubilities of denatured proteins in different organic solvents.

The solubilities of heat-denatured and reduced, S-carboxymethylated proteins have been investigated in various organic solvents. Polar, protic solvents (formic acid, trifluoroacetic acid, 3-mercaptopropionic acid) were found to be good solvents for the denatured proteins (20-40 mg ml-1), and the solubilities of the reduced, S-carboxymethylated proteins were generally higher than those of the heat-denatured forms. Most other organic solvents were less effective in solubilizing the denatured proteins. Apolar solvents did not solubilise denatured proteins, but low solubilizing powers were observed for polar, aprotic solvents. Heat-denaturation was observed to result in the formation of large intermolecular aggregates, which, for ovalbumin and lysozyme, were formed by intermolecular S-S bonds, but for bovine serum albumin involved intermolecular isopeptide bonds.

Electrophoresis, Polyacrylamide Gel↗
PubMed1998

Reactions of denatured proteins with other cellular components to form insoluble aggregates and protection by lactoferrin.

Elucidation of the mechanism of formation of insoluble protein aggregates is essential to resolve problems such as protein folding diseases. In this study the effects of various types of biomolecules on the aggregation of denatured proteins were investigated. Denatured alpha-lactalbumin, an acidic protein, was found to be precipitated by lactoferricin, a basic peptide derived from lactoferrin. Denatured lysozyme, a basic protein, by itself showed aggregation, which was promoted by addition of native alpha-lactalbumin. Heparin and nucleic acids caused almost instant aggregation of denatured lysozyme. Native lactoferricin was also found to aggregate with heparin or nucleic acids. The results show that denatured/misfolded proteins as well as peptides are highly reactive with other cellular components to form insoluble aggregates and suggest a possible mechanism by which protein folding diseases progress. Most of the above aggregation reactions were inhibited by lactoferrin, which could form soluble complexes with denatured alpha-lactalbumin, heparin, and nucleic acids.

Heparin↗
PubMed1997

Protein denaturation induced by cyclic silicone.

While it has been demonstrated that such low-molecular-weight cyclic silicones as octamethylcyclotetrasiloxane (D4) exhibit adjuvant activity, the mechanism of immunological response to silicone is still not clear. This study therefore used fluorescence and circular dichroism (CD) spectroscopy to investigate the denaturation and conformational change of two proteins, fibronectin (Fn) and fibrinogen (Fbg), induced by D4 in vitro. Incubating D4 with Fbg or Fn at D4-to-protein ratios of > 100 or for > 10 h yielded white and mould-like precipitates of the proteins, indicating massive denaturation and aggregation. The fact that the decrease in fluorescence intensity of D4-treated Fn and Fbg was accompanied by a red shift in the maximum wavelength also indicated that denaturation of the proteins had taken place. These changes in fluorescence might result from exposure of tryptophan residuals in the proteins to polar water molecules inasmuch as the denaturation would lead to changes in the tertiary structures of the proteins and rearrangement of the tryptophan residues. The loss of the tertiary structure leads to protein denaturation and, consequently, precipitation. The difference in CD spectra between control Fbg (or Fn) and D4-treated Fbg (or Fn) indicated conformational changes of the proteins when incubated with D4. Thus it has been demonstrated that D4 can induce denaturation and conformational changes in Fbg and Fn and it can be expected that protein molecules that have undergone denaturation or conformational change induced by D4 may act as antigens and stimulate the immune system to generate antibodies, ultimately resulting in autoimmune disease.

Adjuvants, Immunologic↗
PubMed2003

On the origin of residual dipolar couplings from denatured proteins.

Effects of steric obstruction on random flight chains are examined. Spatial probability distributions are elaborated to calculate residual dipolar couplings and residual chemical shift anisotropy, parameters that are acquired by NMR spectroscopy from solutes dissolved in dilute liquid crystals. Calculations yield chain length and residue position-dependent values in good agreement with simulations to provide understanding of recently acquired data from denatured proteins.

Anisotropy↗
PubMed2003

Characterization of denatured proteins by hydrophobic interaction chromatography: a preliminary study.

In this preliminary study hydrophobic interaction chromatography (HIC) is proposed as a good tool in order to detect conformational changes induced by chemical denaturants in two globular proteins, cytochrome C (Cyt C) and myoglobin (MYO). Alterations in protein structure were manifested chromatographically by reproducible changes in peak heights, retention time, and appearance of multiple peaks. The HIC behavior of the two model proteins denatured by guanidinium thyocyanate (GdmSCN) was investigated, keeping constant various concentrations of urea in the mobile phase in a TSK-Gel Phenyl-5PW column (TosoBiosep). Suitable elution conditions provide evidence of the simultaneous presence of two denatured forms in the case of MYO, and sequential different denatured states of Cyt C.

Animals↗
PubMed1992

Influence of transition rates and scan rate on kinetic simulations of differential scanning calorimetry profiles of reversible and irreversible protein denaturation.

The thermodynamic parameters characterizing protein folding can be obtained directly using differential scanning calorimetry (DSC). They are meaningful only for reversible unfolding at equilibrium, which holds for small globular proteins; however, the unfolding or denaturation of most large, multidomain or multisubunit proteins is either partially or totally irreversible. The simplest kinetic model describing partially irreversible denaturation requires three states: Formula [see text] We obtain numerical solutions for N, U, and D as a function of temperature for this model and derive profiles of excess specific heat (Cp) in terms of the reduced variables v/ki and k1/k3, where v is the scan rate. The three-state model reduces to the two-state reversible or irreversible models for very large or very small values of k1/k3, respectively. The apparent transition temperature (Tapp) is always reduced by the irreversible step (U-->D). For all values of k3, Tapp is independent of v/k1 at sufficiently slow scan rates, even when denaturation is highly irreversible, but increases identically for all models at fast scan rates in which case the excess specific heat profile is determined by the rate of unfolding. Accurate values of delta H and delta S can be obtained for the reversible step only when k1 is more than 2000-50,000 times greater than k3. In principle, approximate values for the ratio k1/k3 can be obtained from plots of fraction unfolded vs fraction irreversibly denatured as a function of temperature; however, the fraction irreversibly denatured is difficult to measure accurately by DSC alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Calorimetry, Differential Scanning↗
PubMedDate not supplied

Hyperthermia-induced inhibition of respiration and mitochondrial protein denaturation in CHL cells.

Respiration of Chinese hamster lung V79 cells, as assayed by O2 consumption, increases linearly from 8 to 40 degrees C when plotted in the Arrhenius fashion but is strongly inhibited above 40 degrees C. The protein of mitochondria isolated from V79 cells undergoes structural transitions at 28 and 40 degrees C. This is supported by changes in the fluorescence excitation spectrum of conjugated pyrene maleimide and, to a lesser extent, intrinsic protein fluorophores. Electron spin resonance labelling studies with a derivative of tempo maleimide imply that extensive protein unfolding coincides with the 40 degrees C transition. The structural transition at 40 degrees C correlates well with inhibition of O2 consumption, is irreversible and is probably due to protein denaturation, while the change at 28 degrees C is reversible and has no effect on O2 consumption. Previous studies indicate the presence of a broad lipid transition extending from approximately 8 to 30 degrees C in mitochondrial membranes with all lipids being in the liquid-crystalline state above 30 degrees C. Thus, the onset of the lipid transition may induce the observed protein conformational change at 28 degrees C, but inhibition of respiration above 40 degrees C can be explained by protein denaturation alone. The region from 28 to 40 degrees C of stable protein conformation corresponds to the temperature range of V79 cell growth.

Animals↗
PubMed1994

Molecular dynamics simulation of protein denaturation: solvation of the hydrophobic cores and secondary structure of barnase.

The transition in barnase from the native state to a compact globule has been studied with high-temperature molecular dynamics simulations. A partial destruction of the alpha-helices and the outer strands of the beta-sheet is observed with water molecules replacing the hydrogen bonds of the secondary structural elements. Simultaneously, the main alpha-helix moves away from the beta-sheet and exposes the principal hydrophobic core, many of whose nonpolar side chains, beginning with the ones near the surface, become solvated by hydrogen-bonded water molecules. This step involves a significant increase in the solvent-exposed surface area; the resulting loss of stability due to the hydrophobic effect may be the major source of the activation barrier in the unfolding reaction. The detailed mechanism described here for the first stage of the denaturation of barnase, including the essential role of water molecules, is likely to be representative of protein denaturation, in general.

Bacillus↗
PubMed1995

ATP hydrolysis is required for the DnaJ-dependent activation of DnaK chaperone for binding to both native and denatured protein substrates.

Using two independent experimental approaches to monitor protein-protein interactions (enzyme-linked immunosorbent assay and size exclusion high performance liquid chromatography) we describe a general mechanism by which DnaJ modulates the binding of the DnaK chaperone to various native protein substrates, e.g. lambda P, lambda O, delta 32, P1, RepA, as well as permanently denatured alpha-carboxymethylated lactalbumin. The presence of DnaJ promotes the DnaK for efficient DnaK-substrate complex formation. ATP hydrolysis is absolutely required for such DnaJ-dependent activation of DnaK for binding to both native and denatured protein substrates. Although ADP can stabilize such as an activated DnaK-protein complex, it cannot substitute for ATP in the activation reaction. In the presence of DnaJ and ATP, DnaK possesses the affinity to different substrates which correlates well with the affinity of DnaJ alone for these protein substrates. Only when the affinity of the DnaJ chaperone for its protein substrate is relatively high (e.g. delta 32, RepA) can a tertiary complex DnaK-substrate-DnaJ be detected. In the case that DnaJ binds weakly to its substrate (lambda P, alpha-carboxymethylated lactalbumin), DnaJ is only transiently associated with the DnaK-substrate complex, but the DnaK activation reaction still occurs, albeit less efficiently.

Adenosine Diphosphate↗
PubMed2000

A small heat shock protein cooperates with heat shock protein 70 systems to reactivate a heat-denatured protein.

Small heat shock proteins (sHsps) are a diverse group of heat-induced proteins that are conserved in prokaryotes and eukaryotes and are especially abundant in plants. Recent in vitro data indicate that sHsps act as molecular chaperones to prevent thermal aggregation of proteins by binding non-native intermediates, which can then be refolded in an ATP-dependent fashion by other chaperones. We used heat-denatured firefly luciferase (Luc) bound to pea (Pisum sativum) Hsp18.1 as a model to define the minimum chaperone system required for refolding of a sHsp-bound substrate. Heat-denatured Luc bound to Hsp18.1 was effectively refolded either with Hsc/Hsp70 from diverse eukaryotes plus the DnaJ homologs Hdj1 and Ydj1 (maximum = 97% Luc reactivation with k(ob) = 1.0 x 10(-2)/min), or with prokaryotic Escherichia coli DnaK plus DnaJ and GrpE (100% Luc reactivation, k(ob) = 11.3 x 10(-2)/min). Furthermore, we show that Hsp18.1 is more effective in preventing Luc thermal aggregation than the Hsc70 or DnaK systems, and that Hsp18.1 enhances the yields of refolded Luc even when other chaperones are present during heat inactivation. These findings integrate the aggregation-preventive activity of sHsps with the protein-folding activity of the Hsp70 system and define an in vitro system for further investigation of the mechanism of sHsp action.

Animals↗
PubMed1991

Isoenthalpic and isoentropic temperatures and the thermodynamics of protein denaturation.

The standard enthalpy or entropy change upon transfer of a small nonpolar molecule from a nonaqueous phase into water at a given temperature is generally different for different solute species. However, if the heat capacity change is independent of temperature, there exists a temperature at which the enthalpy or the entropy change becomes the same for all solute species within a given class. Similarly, the enthalpy or the entropy change of protein denaturation, when extrapolated to high temperature assuming a temperature-independent heat capacity change, shows a temperature at which its value becomes the same for many different globular proteins on a per weight basis. It is shown that the existence of these temperatures can be explained from a common formalism based on a linear relationship between the thermodynamic quantity and a temperature-independent molecular property that characterizes the solute or the protein. For the small nonpolar molecule transfer processes, this property is the surface area or the number of groups that are brought in contact with water. For protein denaturation, it is suggested that this property measures the polar/nonpolar mix of the internal interaction within the protein interior. Under a certain set of assumptions, this model leads to the conclusion that the nonpolar and the polar groups of the protein contribute roughly equally to the stability of the folded state of the molecule and that the solvent-accessible surface area of the denatured form of a protein is no more than about two-thirds that of the fully extended form.

Mathematics↗