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At least 73 records · Page 4Linked to original sources
PubMed1996

The concept of a random coil. Residual structure in peptides and denatured proteins.

Non-native states of proteins are of increasing interest because of their relevance to issues such as protein folding, translocation and stability. A framework for interpreting the wealth of experimental data for non-native states emerging from rapid advances in experimental techniques involves comparison with a "random coll' state, which possesses no structure except that inherent in the local interactions. We review here the concept of a random coil, from its global to its local properties. In particular, we focus on the description of a random coil in terms of statistical distributions in psi, phi space. We show that such a model, in combination with experimental data, provides insight into the structural properties of polypeptide chains and has significance for understanding protein folding and for molecular design.

Animals↗
PubMed2006

Nanotube confinement denatures protein helices.

In striking contrast to simple polymer physics theory, which does not account for solvent effects, we find that physical confinement of solvated biopolymers decreases solvent entropy, which in turn leads to a reduction in the organized structural content of the polymer. Since our theory is based on a fundamental property of water-protein statistical mechanics, we expect it to have broad implications in many biological and material science contexts.

Entropy↗
PubMed1999

Modeling of irreversible thermal protein denaturation at varying temperature. II. The complete kinetic model of Lumry and Eyring.

The model for thermal denaturation of proteins involving consecutive reversible and irreversible steps (Lumry and Eyring model) has been analyzed. The most general case, when equilibrium in the first step is established slowly in comparison with the rate of the second step and the heat effect value for the second step is either greater than or less than zero, has been considered. The theoretical dependences of excess heat capacity on temperature have been constructed. The variation of the shape of the theoretical curves with varied values of the enthalpy change for the second step, Arrhenius equation parameters for both steps, and the scanning rate has been studied.

Escherichia coli↗
PubMed1993

Protein denaturation in intact hepatocytes and isolated cellular organelles during heat shock.

There is circumstantial evidence that protein denaturation occurs in cells during heat shock at hyperthermic temperatures and that denatured or damaged protein is the primary inducer of the heat shock response. However, there is no direct evidence regarding the extent of denaturation of normal cellular proteins during heat shock. Differential scanning calorimetry (DSC) is the most direct method of monitoring protein denaturation or unfolding. Due to the fundamental parameter measured, heat flow, DSC can be used to detect and quantitate endothermic transitions in complex structures such as isolated organelles and even intact cells. DSC profiles with common features are obtained for isolated rat hepatocytes, liver homogenate, and Chinese hamster lung V79 fibroblasts. Five main transitions (A-E), several of which are resolvable into subcomponents, are observed with transition temperatures (Tm) of 45-98 degrees C. The onset temperature is approximately 40 degrees C, but some transitions may extend as low as 37-38 degrees C. In addition to acting as the primary signal for heat shock protein synthesis, the inactivation of critical proteins may lead to cell death. Critical target analysis implies that the rate limiting step of cell killing for V79 cells is the inactivation of a protein with Tm = 46 degrees C within the A transition. Isolated microsomal membranes, mitochondria, nuclei, and a cytosolic fraction from rat liver have distinct DSC profiles that contribute to different peaks in the profile for intact hepatocytes. Thus, the DSC profiles for intact cells appears to be the sum of the profiles of all subcellular organelles and components. The presence of endothermic transitions in the isolated organelles is strong evidence that they are due to protein denaturation. Each isolated organelle has an onset for denaturation near 40 degrees C and contains thermolabile proteins denaturing at the predicted Tm (46 degrees C) for the critical target. The extent of denaturation at any temperature can be approximately by the fractional calorimetric enthalpy. After scanning to 45 degrees C at 1 degree C/min and immediately cooling, a relatively mild heat shock, an estimated fraction denaturation of 4-7% is found in hepatocytes, V79 cells, and the isolated organelles other than nuclei, which undergo only 1% denaturation because of the high thermostability of chromatin. Thus, thermolabile proteins appear to be present in all cellular organelles and components, and protein denaturation is widespread and extensive after even mild heat shock.

Animals↗
PubMed1976

The fluorescence decay of tryptophan residues in native and denatured proteins.

The fluorescence decay kinetics at different ranges of the emission spectrum is reported for 17 proteins. Out of eight proteins containing a single tryptophan residue per molecule, seven proteins display multiexponential decay kinetics, suggesting that variability in protein structure may exist for most proteins. Tryptophan residues whose fluorescence spectrum is red shifted may have lifetimes longer than 7 ns. Such long lifetimes have not been detected in any of the denatured proteins studied, indicating that in native proteins the tryptophans having a red-shifted spectrum are affected by the tertiary structure of the protein. The fluorescence decay kinetics of ten denatured proteins studied obey multiexponential decay functions. It is therefore concluded that the tryptophan residues in denatured proteins can be grouped in two classes. The first characterized by a relatively long lifetime of about 4 ns and the second has a short lifetime of about 1.5 ns. The emission spectrum of the group which is characterized by the longer lifetime is red shifted relative to the emission spectrum of the group characterized by the shorter lifetime. A comparison of the decay data with the quantum yield of the proteins raises the possibility that a subgroup of the tryptophan residues is fully quenched. It is noteworthy that despite this heterogeneity in the environment of tryptophan residues in each denatured protein, almost the same decay kinetics has been obtained for all the denatured proteins studied in spite of the vastly different primary structures. It is therefore concluded that each tryptophan residue interacts in a more-or-less random manner with other groups on the polypeptide chain, and that on the average the different tryptophan residues in denatured proteins have a similar type of environment.

Hydrogen-Ion Concentration↗
PubMed2002

Effects of topology and excluded volume on protein denatured state conformational properties.

The conformational constraints on protein denatured states are of prime importance in modulating early events in protein folding. Although structural studies have demonstrated residual structure in protein denatured states, much remains poorly understood with regard to the conformational properties of this state. Here, we investigate topological effects on loop formation probabilities in denatured iso-1-cytochrome c by comparing histidine-heme binding affinities for histidines on the N- versus the C-terminal side of the heme. For histidines N-terminal to the heme (preceding cysteine 14), the polypeptide emerges from the edge of the heme and must simply fold over to bind to the heme. For histidines C-terminal to the heme (following histidine 18), the polypeptide emerges from the back side of the heme and must wrap around the heme for the histidine to bind to the heme. Thus, the steric constraints on this wrap-around topology are expected to be much more demanding than for the heme-edge topology of the N-terminal histidines. Evaluation of loop formation probabilities in 3 M guanidine hydrochloride, conditions that fully denature the variants studied, demonstrates that N-terminal histidine-heme loop formation is 10-25-fold more favorable than C-terminal histidine-heme loop formation, for similar loop sizes. A two-dimensional square lattice model indicates that excluded volume is important in this topological preference. These data provide direct evidence that denatured state topology affects contact probability, and thus probable folding pathways, in a disordered protein.

Base Sequence↗
PubMed2001

Synechocystis HSP17 is an amphitropic protein that stabilizes heat-stressed membranes and binds denatured proteins for subsequent chaperone-mediated refolding.

The small heat shock proteins (sHSPs) are ubiquitous stress proteins proposed to act as molecular chaperones to prevent irreversible protein denaturation. We characterized the chaperone activity of Synechocystis HSP17 and found that it has not only protein-protective activity, but also a previously unrecognized ability to stabilize lipid membranes. Like other sHSPs, recombinant Synechocystis HSP17 formed stable complexes with denatured malate dehydrogenase and served as a reservoir for the unfolded substrate, transferring it to the DnaK/DnaJ/GrpE and GroEL/ES chaperone network for subsequent refolding. Large unilamellar vesicles made of synthetic and cyanobacterial lipids were found to modulate this refolding process. Investigation of HSP17-lipid interactions revealed a preference for the liquid crystalline phase and resulted in an elevated physical order in model lipid membranes. Direct evidence for the participation of HSP17 in the control of thylakoid membrane physical state in vivo was gained by examining an hsp17(-) deletion mutant compared with the isogenic wild-type hsp17(+) revertant Synechocystis cells. We suggest that, together with GroEL, HSP17 behaves as an amphitropic protein and plays a dual role. Depending on its membrane or cytosolic location, it may function as a "membrane stabilizing factor" as well as a member of a multichaperone protein-folding network. Membrane association of sHSPs could antagonize the heat-induced hyperfluidization of specific membrane domains and thereby serve to preserve structural and functional integrity of biomembranes.

Cell Membrane↗