Significance of α-crystallin heteropolymer with a 3:1 αA/αB ratio: chaperone-like activity, structure and hydrophobicity

2008 ◽  
Vol 414 (3) ◽  
pp. 453-460 ◽  
Author(s):  
P. N. B. S. Srinivas ◽  
P. Yadagiri Reddy ◽  
G. Bhanuprakash Reddy
Keyword(s):  
Elevated Temperatures ◽  
Tertiary Structure ◽  
Small Heat Shock Protein ◽  
Molar Ratio ◽  
Eye Lens ◽  
Structural Perturbation ◽  
Structure Changes ◽  
Activity Structure ◽  
Structural Perturbations ◽  
Optimal Protection

The small heat-shock protein α-crystallin isolated from the eye lens exists as a large (700 kDa) heteropolymer composed of two subunits, αA and αB, of 20 kDa each. Although trace amounts of αA-crystallin are found in other tissues, non-lenticular distribution of α-crystallin is dominated by the αB homopolymer. In most vertebrate lens, the molar ratio of αA to αB is generally 3:1. However, the importance of this ratio in the eye lens is not known. In the present study, we have investigated the physiological significance of the 3:1 ratio by determining the secondary/tertiary structure, hydrophobicity and chaperone-like activity of αA- and αB-homopolymers and heteropolymers with different ratios of αA to αB subunits. Although, under physiologically relevant conditions, the αB-homopolymer (37–40 °C) has shown relatively higher activity, the αA-homopolymer or the heteropolymer with a higher αA proportion (3:1 ratio) has shown greater chaperone-like activity at elevated temperatures (>50 °C) and also upon structural perturbation. Furthermore, higher chaperone activity at elevated temperatures as well as upon structural perturbation is mainly mediated through increased hydrophobicity of αA. Although homopolymers and heteropolymers of α-crystallin did not differ in their secondary structure, changes in tertiary structure due to structural perturbations upon pre-heating are mediated predominantly by αA. Interestingly, the heteropolymer with higher αA proportion (3:1) or the αA-homopolymer seems to be better chaperones in protecting lens β- and γ-crystallins at both normal and elevated temperatures. Thus lens might have favoured a combination of these qualities to achieve optimal protection under both native and stress (perturbed) conditions for which the heteropolymer with αA to αB in the 3:1 ratio appears to be better suited.

Unfolding and refolding of a quinone oxidoreductase: α-crystallin, a molecular chaperone, assists its reactivation

2001 ◽  
Vol 359 (3) ◽  
pp. 547-556 ◽  
Author(s):  
Shradha GOENKA ◽  
Bakthisaran RAMAN ◽  
Tangirala RAMAKRISHNA ◽  
Ch. Mohan RAO
Keyword(s):  
Tertiary Structure ◽  
Small Heat Shock Protein ◽  
Active State ◽  
Eye Lens ◽  
Quinone Oxidoreductase ◽  
Denatured State ◽  
Αb Crystallin ◽  
Partially Unfolded ◽  
Vertebrate Eye ◽  
Denatured States

α-Crystallin, a member of the small heat-shock protein family and present in vertebrate eye lens, is known to prevent the aggregation of other proteins under conditions of stress. However, its role in the reactivation of enzymes from their non-native inactive states has not been clearly demonstrated. We have studied the effect of α-crystallin on the refolding of ∊-crystallin, a quinone oxidoreductase, from its different urea-denatured states. Co-refolding ∊-crystallin from its denatured state in 2.5M urea with either calf eye lens α-crystallin or recombinant human αB-crystallin could significantly enhance its reactivation yield. αB-crystallin was found to be more efficient than αA-crystallin in chaperoning the refolding of ∊-crystallin. In order to understand the nature of the denatured state(s) of ∊-crystallin that can interact with α-crystallin, we have investigated the unfolding pathway of ∊-crystallin. We find that it unfolds through three distinct intermediates: an altered tetramer, a partially unfolded dimer, which is competent to fold back to its active state, and a partially unfolded monomer. The partially unfolded monomer is inactive, exhibits highly exposed hydrophobic surfaces and has significant secondary structural elements with little or no tertiary structure. This intermediate does not refold into the active state without assistance. α-Crystallin provides the required assistance and improves the reactivation yield several-fold.

Characteristics and Applications of Nanostructured Nitrides Synthesized by Vapor Phase Reactions

2005 ◽  
Vol 876 ◽  
Author(s):  
Gerald Ziegenbalg ◽  
Carsten Pätzold ◽  
Ute Ŝingliar ◽  
Rico Berthold
Keyword(s):  
Silicon Nitride ◽  
Amorphous Silicon ◽  
Vapor Phase ◽  
Elevated Temperatures ◽  
Catalyst Support ◽  
Chemical Properties ◽  
Molar Ratio ◽  
Basic Catalyst ◽  
Metal Chlorides ◽  
Amorphous Silicon Nitride

AbstractGas phase ammonolysis of volatile metal chlorides at elevated temperatures is a favorable way to produce nitride or oxynitride nanopowders. Their composition as well as the physico-chemical properties is determined by reaction temperature, molar ratio of the reactants and the residence time of the gases in the reaction zone. Both single and multi component powders can be obtained. Typical particle sizes are in the range of 50 to 350 nm. The specific surface can reach values up to 300 m2/g. Microporous analysis revealed the presence of pores with a diameter between 0.6 and 0.7 nm in amorphous silicon nitride. The powders can be used, depending on the characteristics, as catalyst or basic catalyst support. The paper gives an overview about vapor phase synthesis of single and multi component nitrides as well as the use of amorphous silicon nitride as a basic catalyst support for dehydrogenation of propane.

scholarly journals Photocatalytic water splitting by N-TiO2 on MgO (111) with exceptional quantum efficiencies at elevated temperatures

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Yiyang Li ◽  
Yung-Kang Peng ◽  
Liangsheng Hu ◽  
Jianwei Zheng ◽  
Dharmalingam Prabhakaran ◽  
...  
Keyword(s):  
Water Splitting ◽  
Elevated Temperatures ◽  
Practical Method ◽  
Charge Carriers ◽  
Molar Ratio ◽  
Electron Hole ◽  
Photocatalytic Water Splitting ◽  
The Past ◽  
Electron Hole Pair ◽  
Electric Field Polarization

Abstract Photocatalytic water splitting is attracting enormous interest for the storage of solar energy but no practical method has yet been identified. In the past decades, various systems have been developed but most of them suffer from low activities, a narrow range of absorption and poor quantum efficiencies (Q.E.) due to fast recombination of charge carriers. Here we report a dramatic suppression of electron-hole pair recombination on the surface of N-doped TiO2 based nanocatalysts under enhanced concentrations of H+ and OH−, and local electric field polarization of a MgO (111) support during photolysis of water at elevated temperatures. Thus, a broad optical absorption is seen, producing O2 and H2 in a 1:2 molar ratio with a H2 evolution rate of over 11,000 μmol g−1 h−1 without any sacrificial reagents at 270 °C. An exceptional range of Q.E. from 81.8% at 437 nm to 3.2% at 1000 nm is also reported.

Chlormethylchlorphosphane mit sperrigen Substituenten -Synthese und reduktive Enthalogenierung mit Fe2(CO)9 / Bulky Chloromethylchlorophosphines -Syntheses and Reductive Dehalogenation with Fe2 (CO)9

1997 ◽  
Vol 52 (8) ◽  
pp. 883-894 ◽  
Author(s):  
Jörg Fischer ◽  
Peter Machnitzki ◽  
Othmar Stelzer
Keyword(s):  
Nmr Spectra ◽  
Elevated Temperatures ◽  
Reductive Dehalogenation ◽  
Molar Ratio ◽  
Carbonyl Complex ◽  
Temperature Dependent ◽  
Phenyl Derivative ◽  
H Nmr ◽  
Halogen Exchange ◽  
Stage Synthesis

Chloromethylchlorophosphines R(Cl)P-CH2-Cl (R = C6H11, sec-C4H9, 2,4,6-R′3C6H2; R′ = tBu, iPr) with bulky substituents (1a - 1d) have been prepared by treatment of Cl2P-CH2-Cl with organolithium compounds RLi (R = 2,4,6-R′3C6H2) or Grignard reagents RMgX (R = C6H11, sec-C4H9). For the less bulky phenyl derivative Ph(Cl)P-CH2-Cl (1i) a protected group two stage synthesis has been developed employing Et2N(Cl)P-CH2-Cl as an intermediate. Si-N cleavage reactions between Cl2P-CH2-Cl and R2N-SiMe3 or nucleophilic substitution with Ph2NH yield the amino derivatives R′2N(Cl)P-CH2-Cl (R′ = Ph, Et, iPr) (1e, 1g, 1h). The chloromethylbromophosphines R(Br)P-CH2-Cl (R = Br, C6H11) have been obtained by halogen exchange in 1 and 1a with MgBr2 etherate. 1a, 1e, 1g and 1h exist preferably in an antiperiplanar conformation with respect to the P-C(H2) bond as inferred from the analysis of the 1H(CH2)-NMR spectra. Temperature dependent 1H and 13C {1H} NMR spectra indicate restricted rotational processes in 1h. On reaction of 2a with Fe2(CO)9 the η2,μ3-phosphaalkene cluster 3 is obtained, while with 2b (R = 2,4,6-iPr3C6H2) the μ3-phosphinidene cluster 4 is formed. Reductive dehalogenation of 1c (R = 2,4,6-tBu3C6H2) affords the phosphaalkene complex 6 in addition to the 2,3-dihydrobenzo[b]phosphole complex 5. Treatment of the iron carbonyl complex 7c with Fe2(CO)9 in a 1:1 molar ratio at elevated temperatures leads to a novel μ2-phosphido complex 7b with an ortho-metallated Ph2N substituent.

Possibility to Detect Reproducibly some 5-10 Å Conformational Differences by Conventional Techniques: Physiologically Defined Lattice Transformations in Bacteriophage T4

1978 ◽  
Vol 36 (3) ◽  
pp. 441-449
Author(s):  
E. Kellenberger
Keyword(s):  
Information Processing ◽  
Conformational Changes ◽  
Tertiary Structure ◽  
Bacteriophage T4 ◽  
Control Mechanisms ◽  
Gene Products ◽  
Negative Stain ◽  
Structure Changes ◽  
Absolute Structure ◽  
Better Than

It was demonstrated that during maturation the proteins of the surface lattice of a virus shell undergo conformational changes on the level of quarternary structure. The conventional methods of negative stain and information processing allow for detecting differences between two conformational states of some 5 Å, although the information on the absolute structure and its changes are estimated not to be better than 20-30 Å. Attempts for refining the methods in view of demonstrating tertiary structure changes of the subunits involved are discussed. The general biological relevance of these studies are emphasized, particularly in view of studying control mechanisms operating at the level of gene products.

Purification, Characterization, and Self-Assembly of the Polysaccharides from Allium Schoenoprasum

2020 ◽  
Author(s):  
Fengrui Zhang ◽  
Jun Zheng ◽  
Zeyu Li ◽  
Zixuan Cai ◽  
Fengqiao Wang ◽  
...  
Keyword(s):  
Self Assembly ◽  
Tertiary Structure ◽  
Specific Binding ◽  
Gel Filtration ◽  
Spherical Particles ◽  
Molar Ratio ◽  
Hydrodynamic Behavior ◽  
Solution Behavior ◽  
Cylindrical Micelles ◽  
Allium Schoenoprasum

Abstract Background: Allium schoenoprasum is a world-wide common vegetable while only its leave is used in the food factory. Its stalk is largely discarded, for potential heavy metal accumulations, which eventually lead to an environmental contamination. To fully utilize this vegetable and minimize its metal content, the major polysaccharide content is purified and characterized with chemical and computational approaches.Results: The major polysaccharide component from the stalk of Allium schoenoprasum (AssP) was extracted and purified. The gel filtration chromatography purified AssP exhibited a molecular weight of around 1.6 kDa, which was verified by MALDI-ToF-MS. Monosaccharide analysis revealed its composition as rhamnose: arabinose: galactose: glucose: mannose: fructose with a molar ratio of 0.0264:2.46:3.71:3.35:1.00:9.93, respectively. Multiple NMR analysis revealed its backbone as α-Ara/Glu/Gal-(1→2)-linked and β-D-Fru-(4→5)-linked sugar residues. There was no tertiary structure of this polysaccharide, however, it self-assembled into a homogenous nanoparticle with a diameter of ~600 nm. The solution behavior of this AssP polysaccharide was simulated, and there was no specific binding site on one molecule for another. Association of this polysaccharide was concentration dependent. As the AssP concentration increased, the spherical particles increased their sizes and eventually merged into cylindrical micelles. The diversity of AssP hydrodynamic behavior endowed potential versatility in its applications.Conclusions: AssP was characterized as a polysaccharide with identified monosaccharide compositions and linkage between them. Although there is no tertiary structure in one AssP molecule, self-assembly of AssP molecules could form nanoparticles or micelles depending on its solution concentrations. The unique AssP solution behavior endows itself a potential biomaterial for nanoparticles preparations.

Synthesis of new copolymers based on 2,3,4,5,6-pentafluorostyrene, styrene, α-methylstyrene and 4-fluoro-α-methylstyrene

2019 ◽  
Vol 60 (12) ◽  
pp. 91-95
Author(s):  
Ignat S. Dolgin ◽  
◽  
Pyotr P. Purygin ◽  
Yury P. Zarubin ◽  
◽  
...  
Keyword(s):  
Dielectric Constant ◽  
Dielectric Loss ◽  
Loss Tangent ◽  
Dielectric Loss Tangent ◽  
Elevated Temperatures ◽  
Methylene Chloride ◽  
Research Work ◽  
Molar Ratio ◽  
Methyl Styrene ◽  
Derivatives Of

At the first stages of the research work, a copolymer of styrene and α methyl styrene was synthesized by the method of radical emulsion polymerization in an inert atmosphere of argon. The initiator was ammonium persulfate. The molar ratio of the initial monomers of styrene and α-methylstyrene was 70 : 30, respectively. It was found that copolymers synthesized under special controlled conditions have good values of permittivity and dielectric loss tangent. It should be noted that the choice of emulsifier directly affects the values of these indicators. It was previously shown that the most optimal emulsifier is potassium stearate, using which the best values of the dielectric constant and dielectric loss tangent were achieved. At the second stage of the research work, a number of copolymers were synthesized containing 4-methoxystyrene, 4 methyl styrene and α-methyl styrene in their structure. It was experimentally confirmed that the synthesis procedure may be applicable for the preparation of copolymers based on derivatives of styrene and α-methylstyrene. The resulting series of copolymers is highly soluble in methylene chloride; films of each copolymer sample of different thicknesses were obtained by casting from a solution. For this series of copolymer films, the dielectric constant and dielectric loss tangent were determined. It was found that the best values of permittivity and dielectric loss tangent are possessed by a sample of copolymer 4-methoxystyrene and α-methylstyrene. At the latest stage of the study, copolymers of styrene and 2,3,4,5,6-pentafluorostyrene, α-methylstyrene and 4-fluoro-α-methylstyrene, 2,3,4,5,6-pentafluorostyrene and 4-fluoro-α-methylstyrene were synthesized. These fluorine-containing derivatives of styrene and α-methylstyrene easily enough enter into the reaction of radical emulsion copolymerization. The copolymer yields are 53-76%, calculated on the weight of the starting monomers. The structure of a number of newly synthesized copolymers was confirmed by IR spectroscopy. In the future, it is planned to define the values of dielectric constant and dielectric loss tangent for these copolymer samples. It is planned to study the thermomechanical properties of the samples, since fluorine-containing polymers are a promising material for operation at elevated temperatures.

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