The changes in the far-UV CD signal, intrinsic tryptophan fluorescence and bilirubin absorbance showed that the guanidine hydrochloride (GdnHCl)-induced unfolding of a multidomain protein, human serum albumin (HSA), f...
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The changes in the far-UV CD signal, intrinsic tryptophan fluorescence and bilirubin absorbance showed that the guanidine hydrochloride (GdnHCl)-induced unfolding of a multidomain protein, human serum albumin (HSA), followed a two-state process. However, using environment sensitive Nile red fluorescence, the unfolding and folding pathways of HSA were found to follow a three-state process and an intermediate was detected in the range 0.25-1.5 m GdnHCl. The intermediate state displayed 45% higher fluorescence intensity than that of the native state. The increase in the Nile red fluorescence was found to be due to an increase in the quantum yield of the HSA-bound Nile red. Low concentrations of GdnHCl neither altered the binding affinity of Nile red to HSA nor induced the aggregation of HSA. In addition, the secondary structure of HSA was not perturbed during the first unfolding transition (<1.5 m GdnHCl);however, the secondary structure was completely lost during the second transition. The data together showed that the half maximal loss of the tertiary structure occurred at a lower GdnHCl concentration than the loss of the secondary structure. Further kinetic studies of the refolding process of HSA using multiple spectroscopic techniques showed that the folding occurred in two phases, a burst phase followed by a slow phase. An intermediate with native-like secondary structure but only a partial tertiary structure was found to form in the burst phase of refolding. Then, the intermediate slowly folded into the native state. An analysis of the refolding data suggested that the folding of HSA could be best explained by the framework model.
This paper describes a framework model for proton conduction through gramicidin;a model designed to incorporate information from molecular dynamics and use this to predict conductance properties. The state diagram des...
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This paper describes a framework model for proton conduction through gramicidin;a model designed to incorporate information from molecular dynamics and use this to predict conductance properties. The state diagram describes both motion of an excess proton within the pore as well as the reorientation of waters within the pore in the absence of an excess proton. The model is constructed as the diffusion limit of a random walk, allowing control over the boundary behavior of trajectories. Simple assumptions about the boundary behavior are made, which allow an analytical solution for the proton current and conductance. This is compared with corresponding expressions from statistical mechanics. The random walk construction allows diffusing trajectories underlying the model to be simulated in a simple way. Details of the numerical algorithm are described.
作者：
Li, QLin, SFPeking Univ
Inst Remote Sensing & GIS CyberGIS Studio Beijing 100871 Peoples R China
A Digital City is defined and understood as an information system platform, an information service marketplace and an information resource deployment center, and further research on digital city is undertaken from thi...
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ISBN:
(纸本)7900081585
A Digital City is defined and understood as an information system platform, an information service marketplace and an information resource deployment center, and further research on digital city is undertaken from this viewpoint. Based on the conceptual description of information resource and information value chain, the conceptual definition, framework model and architecture of a Digital City are set forth.
A Digital City is defined and understood as an information system platform,an information service marketplace and an information resource deployment center,and further research on digital city is undertaken from this ...
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A Digital City is defined and understood as an information system platform,an information service marketplace and an information resource deployment center,and further research on digital city is undertaken from this *** on the conceptual description of information resource and information value chain,the conceptual definition,framework model and architecture of a Digital City are set forth.
The structure of the transition state for the rate-limiting step in the folding and association of the homodimeric coiled-coil peptide GCN4-p1, was probed by mutational analysis. A series of quadruple amino acid repla...
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The structure of the transition state for the rate-limiting step in the folding and association of the homodimeric coiled-coil peptide GCN4-p1, was probed by mutational analysis. A series of quadruple amino acid replacements that spanned the helix propensity scale were made at the four external f positions in the heptad repeat. Equilibrium and kinetic circular dichroism studies demonstrate that both the stability and the unfolding and refolding rate constants vary with helix propensity but also reflect interactions of the altered side-chains with their local environments. Pairwise replacements and fragment studies show that the two C-terminal heptads are the likely source of the nucleating helices. Helix-helix recognition between preformed elements of secondary structure plays an important role in this fundamental folding reaction. (C) 2000 Academic Press.
\The high structural resolution of the main transition states for the formation of native structure for the six small proteins of which Phi -values for a large set of mutants have become available, barstar, barnase, c...
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\The high structural resolution of the main transition states for the formation of native structure for the six small proteins of which Phi -values for a large set of mutants have become available, barstar, barnase, chymotrypsin inhibitor 2, Are repressor, the src SH3 domain, and a tetrameric p53 domain reveals that for the first 5 of these proteins: (1) Residues that belong to regular secondary structure have a significantly larger average fraction of native structural consolidation than residues in loops;(2) on the other hand, secondary and tertiary structures have built up to the same degree, or at least a high degree, but nonuniformly distributed over the molecule;(3) the most consolidated parts of each protein molecule in the transition state cluster together, and these clusters contain a significantly higher percentage of residues that belong to regular secondary structure than the rest of the molecule. These observations further reconcile the framework model with the nucleation-condensation mechanism for folding: The amazing speed of protein folding can be understood as caused by the catalytic effect of the formation of clusters of residues which have particularly high preferences for the early formation of regular secondary structure in the presence of significant amounts of tertiary structure interactions. (C) 2000 Wiley-Liss, Inc.
The refolding kinetics of cobrotoxin (CBTX), a small-molecular-weight (similar to 7 kDa) all beta-sheet protein, has been monitored using a variety of biophysical techniques. The secondary structure formation and hydr...
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The refolding kinetics of cobrotoxin (CBTX), a small-molecular-weight (similar to 7 kDa) all beta-sheet protein, has been monitored using a variety of biophysical techniques. The secondary structure formation and hydrophobic collapse occur as distinct events during the refolding of the protein. Complete secondary structure formation occurs prior to the clustering of the hydrophobic residues. The late stage(s) of the refolding pathway of CBTX is characterized by change(s) in the local environment and optical asymmetry of the indole ring of the sole tryptophan residue. The results obtained in the present study, to our knowledge, represent the first unambiguous experimental support for the framework model of protein folding. (C) 1999 Academic Press.
The folding of globular proteins occurs through intermediate states whose characterisation provides information about the mechanism of folding. A major class of intermediate states is the compact 'molten globule&#...
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The folding of globular proteins occurs through intermediate states whose characterisation provides information about the mechanism of folding. A major class of intermediate states is the compact 'molten globule', whose characteristics have been studied intensively in those conditions in which it is stable (at acid pH, high temperatures and intermediate concentrations of strong denaturants). In studies involving bovine carbonic anhydrase, human alpha-lact-albumin, bovine beta-lactoglobulin, yeast phosphoglycerate kinase, beta-lactamase from Staphylococcus aureus and recombinant human interleukin 1 beta, we have demonstrated that a transient intermediate which accumulates during refolding is compact and has the properties of the 'molten globule' state. We show that it is formed within 0.1-0.2 s. These proteins belong to different structural types (beta, alpha + beta and alpha/beta), with and without disulphide bridges and they include proteins with quite different times of complete folding (from seconds to decades of minutes). We propose that the formation of the transient molten globule state occurs early on the pathway of folding of all globular proteins.
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