Stability Of Biopolymers Research Articles

1011 散逸粒子動力学による生体高分子の構造安定性の解析(OS10. 電子・原子・マルチシミュレーションに基づく材料特性評価(3),オーガナイズドセッション講演)

1011 散逸粒子動力学による生体高分子の構造安定性の解析(OS10. 電子・原子・マルチシミュレーションに基づく材料特性評価(3),オーガナイズドセッション講演)

The emulsion flocculation stability of protein–carbohydrate diblock copolymers

The effect of the steric layer thickness on the flocculation stability of β-lactoglobulin–carbohydrate diblock copolymers was assessed. The diblock copolymers were created by conjugating β-lactoglobulin to maltose or a series of different M n maltodextrins using the Maillard reaction. The thickness and spatial arrangement of the interfacial layers were assessed via latex adsorption and selective enzymatic digestion studies. An increase in the molecular weight of the maltodextrin (900, 1900 and 3800 Da) increased the interfacial thickness (1.1, 2.5 and 7.3 nm, respectively). No detectable change to interfacial thickness was observed upon the attachment of maltose. The increase in the interfacial layer thickness scaled with the hydrodynamic size of the carbohydrate. The β-lactoglobulin–maltodextrin conjugates were found to have a diblock architecture, with the protein anchored at the surface and the carbohydrate protruding into the aqueous continuous phase. The stability of oil-in-water emulsions formed using the conjugates was assessed by exposing them to salt (150 mM NaCl or 0–20 mM CaCl 2), heat alone or heat in the presence of 150 mM NaCl. Conjugation of a 900 Da maltodextrin provided sufficient steric stabilization to prevent flocculation in high salt environments. The effect of the (number) density of the steric layer was also assessed by controlling the average number of maltodextrins attached per β-lactoglobulin molecule. The steric layer density at which emulsions became unstable was a function of carbohydrate M n . Emulsions made from the 900 Da maltodextrin conjugate became unstable below a steric layer density of one tail per 7.5 nm 2, whilst emulsions made from the 1900 Da maltodextrin were unstable below a steric layer density of one tail per 9.5 nm 2. This trend was expected and can be explained by the stronger van der Waals attraction that arises from the closer interdroplet separations that are permissible with the shorter maltodextrins. The excellent flocculation stability of Maillard conjugate emulsions is thought to arise from the combined effects of weak electrostatic repulsion from the screened protein surface charge and steric repulsion from the attached carbohydrate layer. This means that attachment of a relatively thin steric layer is enough to stabilize the emulsions against flocculation. These findings have important implications for the development of commercial processes to manufacture protein–carbohydrate Maillard conjugate emulsifiers. Furthermore the work provides a greater empirical understanding of the relationship between interfacial architecture and colloidal stability, and may provide the means for greater theoretical understanding of biopolymer stabilization of interfaces.

Autoregulation of stress response in microorganisms

Examples are considered of the involvement of low-molecular-weight autoregulators in the development of resistance of proliferating microbial cultures to unfavorable environmental impacts of various intensity, including impacts programmed to occur in the developmental cycle ("new medium stress," starvation stress) and nonprogrammed impacts. It was shown that extracellular adaptation factors control the reversible adhesion of cells in submerged cultures and the processes of cell reactivation in the poststress period and are involved in the stabilization of cellular biopolymers (proteins and DNA) and subcellular structures (membranes); the adaptogens of the phenolic type also act as efficient scavengers of reactive oxygen species. The protective effect of the adaptogenic autoregulators is manifested in the increase of resistance of microbial cells to stressors of various nature and in the preservation of the cell proliferative capacity.

The Exclusion of Glycine Betaine from Anionic Biopolymer Surface: Why Glycine Betaine Is an Effective Osmoprotectant but Also a Compatible Solute

Paradoxically, glycine betaine (N,N,N-trimethyl glycine; GB) in vivo is both an effective osmoprotectant (efficient at increasing cytoplasmic osmolality and growth rate) and a compatible solute (without deleterious effects on biopolymer function, including stability and activity). For GB to be an effective osmoprotectant but not greatly affect biopolymer stability, we predict that it must interact very differently with folded protein surface than with that exposed in unfolding. To test this hypothesis, we quantify the preferential interaction of GB with the relatively uncharged surface exposed in unfolding the marginally stable lacI helix-turn-helix (HTH) DNA binding domain using circular dichroism and with the more highly charged surfaces of folded hen egg white lysozyme (HEWL) and bovine serum albumin (BSA) using all-gravimetric vapor pressure osmometry (VPO) and compare these results with results of VPO studies (Hong et al. (2004), Biochemistry, 43, 14744-14758) of the interaction of GB with polyanionic duplex DNA. For these four biopolymer surfaces, we observe that the extent of exclusion of GB per unit of biopolymer surface area increases strongly with increasing fraction of anionic oxygen (protein carboxylate or DNA phosphate) surface. In addition, GB is somewhat more excluded from the surface exposed in unfolding the lacI HTH and from the folded surface of HEWL than expected from their small fraction of anionic surface, consistent with moderate exclusion of GB from polar amide surface, as predicted by the osmophobic model of protein stability (Bolen and Baskakov (2001) J. Mol. Biol. 310, 955-963). Strong exclusion of GB from anionic surface explains how it can be both an effective osmoprotectant and a compatible solute; analysis of this exclusion yields a lower bound on the hydration of anionic protein carboxylate surface of two layers of water (>or=0.22 H(2)O A(-)(2)).

Conference Report: Second Workshop on Polymer and Biopolymer Analysis, Degradation, and Stabilization

The second workshop on polymer and biopolymer analysis, degradation, and stabilization was held at the University of Alicante (Alicante, Spain) on September 24-26, 2003. The organizer of this conference was the Departamento de Quimica Analitica, Nutricion y Bromatologia. The co-organizer was the Department of Civil and Environmental Engineering University of Perugia (Italy). The conference was sponsored by the Universidad Politechnica de Valencia, Instituto Technologico del Plastico (AIMPLAS) and the Saving Bank of Spain (BANCAJA). Dr. Alfonso Jimenez (University of Alicante) was the chairman of the organizing committee.

In Silico Modeling and Conformational Mobility of DNA Duplexes

The review is focused on issues of transferability of the context-sensitive conformational characteristics of DNA estimated from crystallographic structural data on the DNA in aqueous solution. The state of the art in molecular dynamics of charged biopolymers in aqueous solution is covered. Elaboration of expedient force fields and algorithms of calculating long-range electrostatic interactions and solving combined equations of atomic motion have made it possible to generate stable nanosecond trajectories of thermal atomic motion of the biopolymer in aqueous solution in the presence of counterions and salt ions over reasonable time. Tools for analyzing the atomic statistical trajectories of DNA duplexes in aqueous solution to infer context-dependent conformational dynamic characteristics are discussed together with advances in simulating the mechanisms of global axial bend in DNA duplexes. These techniques allow one to consecutively analyze relationships between the contextual composition of the duplex and the basic modes of essential motions, their amplitude and extent of fluctuation. Development of satisfactory methods for estimating the free energy of biopolymer conformations in solution permits qualitative assessment of the conformational thermodynamic stability of biopolymers and their complexes.

Methods of computer modeling and conformational mobility of DNA duplexes

The review is focused on issues of transferability of the context-sensitive conformational characteristics of DNA estimated from crystallographic structural data on the DNA in aqueous solution. The state of the art in molecular dynamics of charged biopolymers in aqueous solution is covered. Elaboration of expedient force fields and algorithms of calculating long-range electrostatic interactions and solving combined equations of atomic motion have made it possible to generate stable nanosecond trajectories of thermal atomic motion of the biopolymer in aqueous solution in the presence of counterions and salt ions over reasonable time. Tools for analyzing the atomic statistical trajectories of DNA duplexes in aqueous solution to infer context-sensitive conformational dynamic characteristics are discussed together with advances in simulating the mechanisms of global axial bend in DNA duplexes. These techniques allow one to consecutively analyze relationships between the contextual composition of the duplex and the basic modes of essential motions, their amplitude and extent of fluctuation. Development of satisfactory methods for estimating the free energy of biopolymer conformations in solution permits qualitative assessment of the conformational thermodynamic stability of biopolymers and their complexes.

Kinetic Stabilization of Biopolymers in Single-Crystal Hosts: Green Fluorescent Protein in α-Lactose Monohydrate

Kinetic Stabilization of Biopolymers in Single-Crystal Hosts: Green Fluorescent Protein in α-Lactose Monohydrate

Dictation of the shape of mesoscale semiconductor nanoparticle assemblies by plasmid DNA

We have developed a method of semiconductor nanostructure fabrication relying on the size and shape of a polynucleotide to dictate the overall structure of an assembly of individual nanoparticles. This is exemplified by our use of the 3455-basepair circular plasmid DNA molecule pUCLeu4 which, when anchored to a suitably derivatized substrate, yields an array of semiconductor nanoparticles matching the shape of the biopolymer stabilizer. The viability of the methodology was confirmed using data from high resolution transmission electron microscopy, selected area electron diffraction, and linear optical absorption spectroscopy. This is a unique demonstration of the self-assembly of mesoscale semiconductor nanostructures using biological macromolecules as templates.

生体高分子への圧力効果と水の役割

The application of high pressure technology to food processing and bioscience is a current topic. Water is the main component in such multicomponent systems to control their macroscopic properties and function. Under high pressure, water is not only the medium propagating pressure, but also it affects the stability and function of biopolymers through the modification of hydrogen bonds, hydrophobic and electrostatic interactions. This review is devoted to demonstrate how the biopolymer-water interaction (hydration) is related to the pressure effects on its structural stability, focusing on the compressibility, pressure denaturation, and gelation of proteins.

On the role of water in molecular recognition and self-assembly

The conventional concept of hydrophobic interaction is generalized to include any kind of solvent-induced effects on the binding of two or more solutes in aqueous solutions. Specifically, we focus on the role of hydrogen-bonding between the solutes and solvent molecules. A qualitative examination of the solute-solvent hydrogen-bonding effect on molecular recognition, self-assembly, and stabilization of biopolymers shows that these effects might be quite large and possible more important than direct interactions between solute particles.

Salt effects in the glutathione-facilitated reactivation of reduced bovine pancreatic ribonuclease.

The rate of regeneration of reduced RNase by glutathione was examined in the presence of several added substances: substrate, phospholipid, other proteins, bacterial ribosomes, and neutral salts. Of these, only neutral salts showed substantial effects. K2HOP4 and (NH4)2SO4 strongly accelerated regeneration, the alkali chlorides showed moderate acceleration or inhibition, while LiBr and KSCN strongly inhibited. The t1/2 for regeneration in 1 M Pi is 4 min compared to 75 min in the absence of Pi; in 0.5 M KSCN t1/2 greater than 100 min. The pattern of specific salt effects is similar to a Hofmeister series. There is a strong parallel between the pattern of specific salt effects on the kinetics of RNase regeneration and the pattern of effects of the same salts on the equilibrium stability of biopolymers. This suggests that the role of salts in the regeneration is to stabilize or destabilize rate-limiting folding intermediates. Pi-accelerated glutathione regenerations showed a broad temperature optimum from 30-37 degrees. In strong contrast with the virtual concentration independence of the Pi-free controls, with Pi = 1 M, both rates and yields of RNase activity were decreased markedly at [RNase] greater than 2 x 10(-6) M. Phosphate and pyrophosphate showed additive, and in some cases, synergistic accelerations. These results suggest that specific ion binding occurs in addition to general solvent effects.

Base pairing of adenine and uracil derivatives in the presence of water.

AbstractThe association of chloroform‐soluble derivatives of uracil and adenine has been examined in chloroform solution in the presence of dissolved water. Analysis by infrared spectroscopy shows that complex formation still occurs in these conditions, and that the extent of association is substantially unchanged by the presence of water. Evidence is presented for the coexistence of two kinds of base pair (involving, respectively, the C2 and C4 carbonyl groups of the pyrimidine) in the solutions, and for some displacement in their relative balance by the added water. The binding of water to the C2 and C4 carbonyl groups can be separately observed in both the free uracil derivative and its 1:1 complex with 9‐ethyladenine. Little or no competition has been found to occur between the formation of base pairs and binding of water to the bases, as judged by measurements of water solubility in chloroform solutions of the bases individually and in 1:1 mixtures. The evidence suggests that this phenomenon can be largely explained by the formation of double hydrogen bonds by the uracil carbonyl groups. Taken together with recent published observations, the results indicate that hydrogen bonding may make a much greater energetic contribution to conformational stability of biopolymers in aqueous solution that has been supposed.

Coordinative Binding of Divalent Cations with Ligands Related to Bacterial Spores: Equilibrium Studies

It has been repeatedly postulated that the high heat resistance of bacterial spores is due to stabilization of biopolymers in the spore interior by a solid deposit of protective cement consisting of coordination complexes of ligands with divalent metal ions. This report presents data on metal-binding characteristics of some of the ligands related to spores as determined by means of potentiometric equilibrium measurements under conditions of temperature and ionic strength (t = 25.0 degrees C; mu = 1.0 KNO(3)) identical with those reported earlier by the authors in order to facilitate correlation by using comparable data. The spore ligands investigated in this study included 2,6-pyridinedicarboxylic acid (DPA), alpha,epsilon-diaminopimelic acid, D-glutamic acid, and D-alanine in a ratio of 1:1 with metal ions which are known to play a role in heat resistance of spores. Stability constants of the chelates of these spore ligands with metal ions such as Ca(II), Mg(II), Cu(II), Ni(II), Zn(II), Co(II), and Mn(II) have been determined. In general the metal chelates of DPA exhibited the greatest stability. On the basis of a consideration of the stability data together with the known configurations of the ligand and the coordination requirements of the metal ions, possible structures indicating the coordinate binding of the spore ligands with the metal ions are presented. All the metal chelates except those of Ca(II) were found to undergo hydrolysis and separation of solid phase in the pH range 7-8.5. The relatively greater hydrolytic stability of Ca(II) chelates and the high affinity of DPA for metal ions appear to be of biological significance insofar as these two spore components are more widely associated with the heat resistance of bacterial spores.

Mixed Chelates of Ca(II)-Pyridine-2,6-Dicarboxylate with Some Amino Acids Related to Bacterial Spores

The high resistance of bacterial spores to heat has been repeatedly postulated to be due to stabilization of spore biopolymers by metal chelate compounds. Binding of calcium dipicolinic acid (Ca(II)-DPA) with spore proteins and amino acids has been discussed in the literature, but equilibrium data are generally lacking. By means of potentiometric pH titrations at 25 degrees C and an ionic strength of 1.0 (KNO(3)), the formation of Ca(II)-DPA (1:1 and 1:2) chelates and the interactions of Ca(II)-DPA chelate with a mole of each of three typical amino acids viz., cysteine, alanine, and glycine has been investigated. Analysis of the potentiometric data indicates that calcium and DPA forms 1:1 and 1:2 chelates with log K(ML1) = 4.39 +/- 0.01 and log K(ML2) = 2.25 +/- 0.01. In the presence of an equimolar amount of each of the amino acids under consideration, the Ca(II)-DPA chelate forms mixed ligand (ternary) chelate yielding the following stepwise stability constants: log K(1) = 4.17 +/- 0.01, log K(2) = 0.78 +/- 0.01 for cysteine, log K(1) = 4.06 +/- 0.01, log K(2) = 0.65 +/- 0.01 for alanine, and log K(1) = 4.30 +/- 0.02, log K(2) = 0.11 +/- 0.01 for glycine. Methods for calculating the stability constants of the mixed ligand system have been developed. On the basis of the potentiometric equilibrium data, possible structures for the various calcium chelate species are discussed. The data suggest that the differences in heat resistance of various strains of bacterial spores may conceivably be related to the differences in composition and stability of coordination complexes in the spore.