Relationship between functional properties and structure of ovalbumin

Non-sticky SiNx nanonets for single protein denaturation analysis

Proteins play crucial roles in nearly all biological activities, with their functional structures deriving from stable folded conformations. Protein denaturation, induced by chemical and physical agents, is a complex process where proteins lose their stable structures, thereby impairing their biological functions. Characterizing protein denaturation at the single-molecule level remains a significant challenge. In this study, we developed non-adhesive silicon nitride nanonets coated with polyethylene glycol to capture individual proteins. We utilized these nanonets to investigate the denaturation of ovalbumin induced by guanidine hydrochloride (Gdn-HCl) and lead chloride. The entire denaturation and renaturation processes of a single ovalbumin molecule were monitored via ionic current measurements through the nanonets. These non-sticky nanonets offer a versatile tool for real-time studies of structural changes during protein denaturation.

Broadening the Scope of Polyoxometalates as Artificial Proteases in Surfactant Solutions: Hydrolysis of Ovalbumin by Zr(IV)-Substituted Keggin Complex

Development of catalysts for the selective hydrolysis of proteins is challenging, yet important for many applications in biotechnology and proteomics. The hydrolysis of hydrophobic proteins is particularly challenging, as due to their poor solubility, the use of surfactants is often required. In this study, the proteolytic potential of catalyst systems based on the Zr(IV)-substituted Keggin polyoxometalate (Et2NH2)10[Zr(PW11O39)2] (Zr-K 1:2) and three different surfactants (ionic SDS (sodium dodecyl sulfate); zwitterionic Zw3-12 (n-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate); and CHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate)), which differ in structure and polarity, has been investigated. Hydrolysis of ovalbumin (OVA) was examined in the presence of Zr-K 1:2 and surfactants by sodium dodecyl sulfate poly(acrylamide) gel electrophoresis (SDS-PAGE), which showed the appearance of new polypeptide fragments at lower molecular weight, indicating that selective hydrolysis of OVA took place for all three catalyst systems. The same fragmentation pattern was observed, showing that the selectivity was not affected by surfactants. However, the surfactants influenced the performance of the catalyst. Hence, the interactions of OVA with surfactants and Zr-K 1:2 were investigated using different techniques such as tryptophan fluorescence, Circular Dichroism, and Dynamic Light Scattering. The speciation of the catalyst in surfactant solutions was also followed by 31P Nuclear Magnetic Resonance spectroscopy providing insight into its stability under reaction conditions.

An α-tocopheryl succinate enzyme-based nanoassembly for cancer imaging and therapy

Nanoassembly (NA) based on a D-α-tocopherol succinate (αTS) conjugated lysozyme (Lys) (Lys-αTS) was fabricated for tumor-selective delivery of curcumin (CUR) for breast cancer therapy. Lys and αTS were used as a biocompatible enzyme and a hydrophobic residue, respectively, for the preparation of nanocarriers in this study. Compared with CUR-loaded cross-linked Lys (c-Lys/CUR) NA, Lys-αTS/CUR NA exhibited a smaller hydrodynamic size (213 nm mean diameter), a narrower size distribution, and a more spherical shape. Sustained drug release was observed from the Lys-αTS/CUR NA for five days at a normal physiological pH (pH 7.4). The developed Lys-αTS/CUR NA showed enhanced cellular accumulation, antiproliferative effects, and apoptotic efficacies in MDA-MB-231 human breast adenocarcinoma cells. According to the results of optical imaging test in the MDA-MB-231 tumor-bearing mouse models, the Lys-αTS/CUR NA-injected group exhibited a more tumor-selective accumulation pattern, rather than being distributed in the normal tissues and organs. The observed tumor targetability of Lys-αTS/CUR was further studied, which revealed improved in vivo anticancer activities (better inhibition of tumor growth and induction of apoptosis in the tumor tissue) after an intravenous administration in the MDA-MB-231 tumor-bearing mouse models. All these results indicate that the newly developed enzyme-based nanocarrier, the Lys-αTS NA, can be a promising candidate for the therapy of breast cancers.

Protein delivery nanosystem of six-arm copolymer poly(ε-caprolactone)-poly(ethylene glycol) for long-term sustained release

Background

To address the issue of delivery of proteins, a six-arm copolymer, six-arm poly (ε-caprolactone)–poly(ethylene glycol) (6S-PCL-PEG), was synthesized by a simple two-step reaction. Thereafter, the application of 6S-PCL-PEG as a protein carrier was evaluated.

Materials and methods

A six-arm copolymer, six-arm poly(ε-caprolactone) (6S-PCL), was synthesized by ring-opening polymerization, with stannous octoate as a catalyst and inositol as an initiator. Then, poly(ethylene glycol) (PEG) was linked with 6S-PCL by oxalyl chloride to obtain 6S-PCL-PEG. Hydrogen-1 nuclear magnetic resonance spectrum, Fourier-transform infrared spectroscopy, and gel-permeation chromatography were conducted to identify the structure of 6S-PCL-PEG. The biocompatibility of the 6S-PCL-PEG was evaluated by a cell counting kit-8 assay. Polymeric nanoparticles (NPs) were prepared by a water-in-oil-in-water double emulsion (W₁/O/W₂) solvent evaporation method. The size distribution and zeta potential of NPs were determined by dynamic light scattering. Transmission electron microscopy was used to observe the morphology of NPs. Drug-loading capacity, encapsulation efficiency, and the release behavior of ovalbumin (OVA)-loading NPs were tested by the bicinchoninic acid assay kit. The stability and activity of OVA released from NPs were detected and the uptake of NPs was evaluated by NIH-3T3 cells.

Results

All results indicated the successful synthesis of amphiphilic copolymer 6S-PCL-PEG, which possessed excellent biocompatibility and could formulate NPs easily. High drug-loading capacity and encapsulation efficiency of protein NPs were observed. In vitro, OVA was released slowly and the bioactivity of OVA was maintained for over 28 days.

Conclusion

6S-PCL-PEG NPs prepared in this study show promising potential for use as a protein carrier.

Egg proteins as allergens and the effects of the food matrix and processing

Hen eggs are an important and inexpensive source of high-quality proteins in the human diet. Egg, either as a whole or its constituents (egg yolk and white), is a key ingredient in many food products by virtue of its nutritional value and unique functional properties, such as emulsifying, foaming, and gelling. Nevertheless, egg is also known because of its allergenic potential and, in fact, it is the second most frequent source of allergic reactions, particularly in children. This review deals with the structural or functional properties of egg proteins that make them strong allergens. Their ability to sensitize and/or elicit allergic reactions is linked to their resistance to gastroduodenal digestion, which ultimately allows them to interact with the intestinal mucosa where absorption occurs. The factors that affect protein digestibility, whether increasing it, decreasing it, or inducing a different proteolysis pattern, and their influence on their capacity to induce or trigger an allergic reaction are discussed. Special attention is paid to the effect of the food matrix and the processing practices on the capacity of egg proteins to modulate the immune response.

pH-Responsive Poly(D,L-lactic-co-glycolic acid) Nanoparticles with Rapid Antigen Release Behavior Promote Immune Response

In the quest to treat intracellular infectious diseases and virus infection, nanoparticles (NPs) have been considered to be efficient tools for inducing potent immune responses, specifically cellular immunity. Antigen processing and presenting by antigen presenting cells (APCs) could influence immune response, especially the priming of T-cell-mediated cellular immunity. Here, we fabricated pH-responsive poly(D,L-lactic-co-glycolic acid) (PLGA) NPs with rapid antigen intracellular release behavior in APCs. The NPs, which had thin shells and large inner space, contain ammonium bicarbonate (NH4HCO3), which could regulate release in endosomes and lysosomes, acting as an antigen release promoter in dendritic cells (DCs), and were coencapsulated with antigen (ovalbumin, OVA). Hydrogen ions (H(+)) in DC endosomes and lysosomes (pH ∼5.0 and 6.5) could react with NH4HCO3 to generate NH3 and CO2, which broke NPs and released antigens. After uptake by DCs, antigens encapsulated in pH-responsive PLGA NPs could escape from lysosomes into the cytoplasm and be cross-presented. Moreover, the NPs induced up-regulation of co-stimulatory molecules and stimulated cytokine production. Mouse immunization with pH-responsive PLGA NPs induced greater lymphocyte activation, more antigen-specific CD8(+) T cells, stronger cytotoxic capacity (IFN-γ and granzyme B), enhanced antigen-specific IgG antibodies, and higher serum IgG2a/IgG1, indicating cellular immunity. The NPs also improved generation of memory T cells to protect against reinfection. Thus, pH-responsive PLGA NPs, which induced strong cellular immune responses and offered antibody protection, could be potentially useful as effective vaccine delivery and adjuvant systems for the therapy of intracellular infectious diseases and virus infection.

Development of enteric submicron particle formulation of papain for oral delivery

BACKGROUND

Particulate systems have received increasing attention for oral delivery of biomolecules. The objective of the present study was to prepare submicron particulate formulations of papain for pH-dependent site-specific release using pH-sensitive polymers.

METHODS

Enteric submicron particle formulations of papain were prepared by w/o/w emulsion solvent evaporation using hydroxypropyl methylcellulose phthalate (HPMCP), Eudragit L100, and Eudragit S100, to avoid gastric inactivation of papain.

RESULTS

Smaller internal and external aqueous phase volumes provided maximum encapsulation efficiency (75.58%-82.35%), the smallest particle size (665.6-692.4 nm), and 25%-30% loss of enzyme activity. Release studies in 0.1 N HCl confirmed the gastroresistance of the formulations. The anionic submicron particles aggregated in 0.1 N HCl (ie, gastric pH 1.2) due to protonation of carboxylic groups in the enteric polymer. Aggregates < 500 μm size would not impede gastric emptying. However, at pH > 5.0 (duodenal pH), the submicron particles showed deaggregation due to restoration of surface charge. HPMCP submicron particles facilitated almost complete release of papain within 30 minutes at pH 6.0, while Eudragit L100 and Eudragit S100 particles released 88.82% and 53.00% of papain at pH 6.8 and pH 7.4, respectively, according to the Korsmeyer-Peppas equation. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and fluorescence spectroscopy confirmed that the structural integrity of the enzyme was maintained during encapsulation. Fourier transform infrared spectroscopy revealed entrapment of the enzyme, with powder x-ray diffraction and differential scanning calorimetry indicating an amorphous character, and scanning electron microscopy showing that the submicron particles had a spherical shape.

CONCLUSION

In simulated gastrointestinal pH conditions, the HPMCP, Eudragit L100, and Eudragit S100 submicron particles showed good digestion of paneer and milk protein, and could serve as potential carriers for oral enzyme delivery. Stability studies indicated that formulations with approximately 6% overage would ensure a two-year shelf-life at room temperature.

Evaluation of protein stability and in vitro permeation of lyophilized polysaccharides-based microparticles for intranasal protein delivery

Biocompatible microparticles prepared by lyophilization were developed for intranasal protein delivery. To test for the feasibility of this formulation, stability of the incorporated protein and enhancement of in vitro permeation across the nasal epithelium were evaluated. Lyophilization was processed with hydroxypropylmethylcellulose (HPMC) or water soluble chitosan (WCS) as biocompatible polymers, hydroxypropyl-β-cyclodextrin (HP-β-CD) and d-alpha-tocopheryl poly(ethylene glycol 1000) succinate (TPGS 1000) as permeation enhancers, sugars as cryoprotectants and lysozyme as the model protein. As a result, microparticles ranging from 6 to 12μm were developed where the maintenance of the protein conformation was verified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), circular dichroism and fluorescence intensity detection. Moreover, in vitro bioassay showed that the lysozyme activity was preserved during the preparation process while exhibiting less cytotoxicity in primary human nasal epithelial (HNE) cells. Results of the in vitro release study revealed slower release rate in these microparticles compared to that of the lysozyme itself. On the other hand, the in vitro permeation study exhibited a 9-fold increase in absorption of lysozyme when prepared in lyophilized microparticles with HPMC, HP-β-CD and TPGS 1000 (F4-2). These microparticles could serve as efficient intranasal delivery systems for therapeutic proteins.

Egg white ovalbumin digestion mimicking physiological conditions

Gastrointestinal digestion of ovalbumin (OVA) was simulated using an in vitro system in two steps, which mimicked digestion in the stomach and duodenum, to assess the effect of different gastric pHs, different concentrations of proteases, and the presence of surfactants, such as phosphatidylcholine (PC) and bile salts (BS). OVA was very resistant to pepsin action at an enzyme/substrate ratio that would resemble a physiological situation (1:20 w/w, 172 units/mg) at pH values equal or above 2. The presence of PC did not change the susceptibility of OVA to proteolysis with pepsin. Fluorescence experiments showed that OVA interacted with PC vesicles, particularly at acidic pH, but it is likely that the protein maintained a high degree of conformational stability, resisting pepsin action. The presence of BS at physiological concentrations considerably increased the proteolysis of OVA by a mixture of pancreatic enzymes. The addition of PC made OVA even more sensitive to proteolytic degradation, suggesting that OVA could associate with the surfactants under duodenal conditions, increasing its exposure to pancreatic proteinases. Immunoreactivity against IgE from sera of allergic patients was retained after in vitro gastric digestion, depending on the reactivity of the sera, but it decreased considerably after in vitro duodenal digestion.

Amphiphilic polyanhydrides for protein stabilization and release

The overall goal of this research is to design novel amphiphilic biodegradable systems based on polyanhydrides for the stabilization and sustained release of peptides and proteins. Accordingly, copolymers of the anhydrides, 1,6-bis(p-carboxyphenoxy)hexane (CPH) and 1,8-bis(p-carboxyphenoxy)-3,6-dioxaoctane (CPTEG), which are monomer-containing oligomeric ethylene glycol moieties, have been synthesized. Microspheres of different CPTEG:CPH compositions have been fabricated by two non-aqueous methods: solid/oil/oil double emulsion and cryogenic atomization. The ability of this amphiphilic polymeric system to stabilize model proteins (i.e., lysozyme and ovalbumin) was investigated. The structure of both the encapsulated as well as the released protein was monitored using gel electrophoresis, circular dichroism, and fluorescence spectroscopy. It was found that the CPTEG:CPH system preserves the structural hierarchy of the encapsulated proteins. Activity studies of the released protein indicate the CPTEG:CPH system retains the biological activity of the released protein. These results are promising for future in vivo studies, which involve the design of novel biodegradable polyanhydride carriers for the stabilization and sustained release of therapeutic peptides and proteins.

Relationship between seawater pollution and qualitative changes in the extracted proteins from mussels Mytilus galloprovincialis

The aim of this study was to find a reliable biomarker of seawater pollution. For this purpose the contents of Zn and Cu, proteins and antioxidant activity in mussels Mytilus galloprovincialis collected from polluted and non-polluted sites of the Bulgarian Black Sea coast were compared. To determine the above-mentioned indices atomic spectroscopy, Fourier Transform Infrared (FT-IR) spectroscopy, fluorescence, differential scanning calorimetry (DSC), and two antioxidant tests were used. It was found that the amounts of Zn and Cu were significantly higher in the mussel proteins from the polluted than from the non-polluted sites (P<0.05). FT-IR spectroscopy and fluorescence revealed specific qualitative changes in secondary and tertiary structures in mussel proteins in the samples from polluted sites. The thermodynamic properties of proteins and the changes upon denaturation were correlated with the secondary structure of proteins and disappearance of alpha-helix. Purified protein scavenging activity against 2, 2'-azinobis (3-ethylbenzothiazoline-6-sulfonate) radical cation (ABTS(*+)) was significantly higher in mussel samples from polluted than from non-polluted sites. Therefore, the changes in Zn and Cu concentration, in protein's secondary and tertiary structures and antioxidant activity in mussels M. galloprovincialis from polluted sites can be a reliable biomarker of the level of the seawater pollution.

Flow injection analysis with diode array absorbance detection and dynamic surface tension detection for studying denaturation and surface activity of globular proteins

In this article, a multidimensional dynamic surface tension detector (DSTD), in a parallel configuration with a UV-visible diode array absorbance detector, is presented in a novel flow injection analysis (FIA) application to study the effects of chemical denaturants urea, guanidinium hydrochloride (GdmHCl), and guanidinium thyocyanate (GdmSCN) on the surface activity of globular proteins at the liquid-air interface. The DSTD signal is obtained by measuring the changing pressure across the liquid-air interface of 4-mul drops repeatedly forming at the end of a capillary using FIA. The sensitivity and selectivity of the DSTD signal is related to the surface-active protein concentration in aqueous solution combined with the thermodynamics and kinetics of protein interaction at a liquid-air drop interface. Rapid on-line calibration and measurement of dynamic surface tension is applied, with the surface tension converted into surface pressure results. Continuous surface tension measurement throughout the entire drop growth is achieved, providing insight into kinetic behavior of protein interactive processes at the liquid-air drop interface. Specifically, chemical denaturation of 12 commercial globular proteins-chicken egg albumin, bovine serum albumin, human serum albumin, alpha-lactalbumin (alpha-Lac), myoglobin, cytochrome c, hemoglobin, carbonic anhydrase, alpha-chymotrypsinogen A, beta-lactoglobulin (beta-LG), lysozyme, and glyceraldehyde-3-phosphate-dehydrogenase-is studied in terms of surface pressure (i.e., surface activity) after treatment with increasing concentrations of urea, GdmHCl, and GdmSCN in the 0-8, 0-6, and 0-5 M ranges, respectively. For several of these proteins, the spectroscopic absorbance changes are monitored simultaneously to provide additional information prior to drop formation. Results show that surface pressure of proteins generally increases as the denaturant concentration increases and that effectiveness is GdmSCN > GdmHCl > urea. Protein unfolding curves obtained by plotting surface pressure as a function of denaturant concentration are presented and compared with respect to unfolding curves obtained by using UV absorbance and literature data. Kinetic information relative to the protein adsorption to the air-liquid interface of two proteins, alpha-Lac and beta-LG (chosen as representative proteins for comparison), denatured by the three denaturants is also studied and discussed.

Heat-induced denaturation and aggregation of ovalbumin at neutral pH described by irreversible first-order kinetics

The heat-induced denaturation kinetics of two different sources of ovalbumin at pH 7 was studied by chromatography and differential scanning calorimetry. The kinetics was found to be independent of protein concentration and salt concentration, but was strongly dependent on temperature. For highly pure ovalbumin, the decrease in nondenatured native protein showed first-order dependence. The activation energy obtained with different techniques varied between 430 and 490 kJ*mole(-1). First-order behavior was studied in detail using differential scanning calorimetry. The calorimetric traces were irreversible and highly scan rate-dependent. The shape of the thermograms as well as the scan rate dependence can be explained by assuming that the thermal denaturation takes place according to a simplified kinetic process where N is the native state, D is denatured (or another final state) and k a first-order kinetic constant that changes with temperature, according to the Arrhenius equation. A kinetic model for the temperature-induced denaturation and aggregation of ovalbumin is presented. Commercially obtained ovalbumin was found to contain an intermediate-stable fraction (IS) of about 20% that was unable to form aggregates. The denaturation of this fraction did not satisfy first-order kinetics.

The behavior of R-ovalbumin and its individual components A1, A2, and A3 in urea solution: kinetics and equilibria

Procedures are described for the isolation of the individual components A1, A2, and A3 of native R-ovalbumin from freshly laid domestic hen eggs. Because heavy metal ion contaminants result in spurious irreproducible kinetics, particularly at high pH, considerable care is taken to avoid their presence. Kinetics studies are made of the behavior of whole R-ovalbumin and its individual components in urea solution over the pH range 3.7-9.6 following the reaction by determining absorbance differences at 233, 287, and 293 nm and ORD and CD changes at 350 and 221 nm, respectively. Reaction is rapid at low pH, slowing with increasing pH. Except under limited conditions, the reaction is not simple first order. Equations are presented for describing the reactions, and the nature of the reaction products is considered. Unfolding equilibrium profiles were also determined by ORD at several wavelengths and were not stigmoidal in shape and the normalized curves were not superimposed.

Behavior of S1- and S2-ovalbumin and S-ovalbumin A1 in urea solution: kinetics and equilibria

The isolation of S-, S1-, and S2-ovalbumin from domestic hen egg R-ovalbumin and of two methods for S-ovalbumin A1 are described. The first is by heat treatment of R-ovalbumin A1 and the second is of R-ovalbumin followed by fractionation on Sepharose. A kinetics and equilibrium study is made of their behavior in the presence of urea and compared with that of R-ovalbumins. As anticipated, the S-ovalbumins are much more resistant to urea than R-ovalbumins. Unlike the latter, S-ovalbumins' equilibrium profiles have a simpler sigmoidal shape. The unfolding of S1- and S2-ovalbumin is an order of magnitude slower than that of R-ovalbumin. Some possible structural differences between R- and S-ovalbumin forms and their significance are discussed.

Structural changes in plasma circulating fibrinogen after moderate beer consumption as determined by electrophoresis and spectroscopy

The effects of short-term moderate beer consumption (MBC) on plasma circulating fibrinogen (PCF) in patients suffering from coronary atherosclerosis were investigated by use of 2-dimensional electrophoresis (2-DE), circular dichroism (CD), and Fourier transform infrared spectroscopy (FT-IR). Forty-eight volunteers after coronary bypass surgery were divided into experimental (EG) and control (CG) groups, each of 24. Patients of the EG group consumed 330 mL of beer/day (about 20 g of alcohol) for 30 consecutive days, and CG volunteers drank mineral water instead of beer. Blood samples were collected before and after the experiment. In 21 out of 24 patients after beer consumption the plasma circulating fibrinogen was compromised: changes in its secondary structure were found. These changes were expressed in relatively low electrophoretic mobility and charge heterogeneity, decrease in alpha-helix and increase in beta-sheet, and in slight shift of amide I and II bands. Our findings indicate that one of the positive benefits of moderate beer consumption is to diminish the production of fibrinogen and its stability, which reduces the potential risk exerted by this protein. Thus, in most of beer-consuming patients some qualitative structural changes in plasma circulating fibrinogen were detected.

Structure characterization of human serum proteins in solution and dry state

The present report describes application of advanced analytical methods to establish correlation between changes in human serum proteins of patients with coronary atherosclerosis (protein metabolism) before and after moderate beer consumption. Intrinsic fluorescence, circular dichroism (CD), differential scanning calorimetry and hydrophobicity (So) were used to study human serum proteins. Globulin and albumin from human serum (HSG and HSA, respectively) were denatured with 8 m urea as the maximal concentration. The results obtained provided evidence of differences in their secondary and tertiary structures. The thermal denaturation of HSA and HSG expressed in temperature of denaturation (Td, degrees C), enthalpy (DeltaH, kcal/mol) and entropy (DeltaS kcal/mol K) showed qualitative changes in these protein fractions, which were characterized and compared with fluorescence and CD. Number of hydrogen bonds (n) ruptured during this process was calculated from these thermodynamic parameters and then used for determination of the degree of denaturation (%D). Unfolding of HSA and HSG fractions is a result of promoted interactions between exposed functional groups, which involve conformational changes of alpha-helix, beta-sheet and aperiodic structure. Here evidence is provided that the loosening of the human serum protein structure takes place primarily in various concentrations of urea before and after beer consumption (BC). Differences in the fluorescence behavior of the proteins are attributed to disruption of the structure of proteins by denaturants as well as by the change in their compactability as a result of ethanol consumption. In summary, thermal denaturation parameters, fluorescence, So and the content of secondary structure have shown that HSG is more stable fraction than HSA.

Characterization of soluble amaranth and soybean proteins based on fluorescence, hydrophobicity, electrophoresis, amino Acid analysis, circular dichroism, and differential scanning calorimetry measurements

Intrinsic fluorescence (IF), surface hydrophobicity (S(o)), electrophoresis, amino acid analysis, circular dichroism (CD), and differential scanning calorimetry (DSC) were used to study folded and unfolded soluble proteins from Amaranthus hypochondriacus (A. h.) and soybean (S). Globulin (Glo) and albumin subfractions (Alb-1 and Alb-2) were extracted from A. h. and S and denatured with urea. Electrophoretic and functional properties indicated a significant correlation between soluble protein fractions from soybean and amaranth. The protein fractions shared some common electrophoretic bands as well as a similar amino acid composition. The larger percent of denaturation in protein fractions, which is associated with enthalpy and the number of ruptured hydrogen bonds, corresponds to disappearance of alpha-helix. The obtained results provided evidence of differences in their secondary and tertiary structures. The most stable was Glo followed by the Alb-2 fraction. Predicted functional changes in model protein systems such as pseudocereals and legumes in response to processing conditions may be encountered in pharmaceutical and food industries. These plants can be a substitute for some cereals.

Unfolding and inactivation of monomeric superoxide dismutase from E. coli by SDS

The inactivation and the unfolding of the naturally monomeric Cu, Zn, superoxide dismutase from E. coli upon addition of sodium dodecylsulphate have been studied. In contrast to the bovine enzyme, CD, EPR, NMR spectroscopy and pulsed low resolution NMR measurements found an unfolding transition followed by inactivation of the enzyme. During this transition the active site becomes accessible to the bulk water. The unfolding is reversible and both, the tridimensional structure of the protein and the active site, can be restored upon dialysis. In addition, unfolding occurs without loss of metals in the solution.

Intrinsic tryptophan fluorescence of human serum proteins and related conformational changes

The unfolding of human serum proteins (HSP) was studied by measuring the intrinsic fluorescence intensity at a wavelength of excitation corresponding to tryptophan's or typosine's fluorescence and surface hydrophobicity. The maxima emission wavelengths (lambdamax) of human serum albumin (HSA) and human serum globulin (HSG) before beer consumption (BC) were 336.0 and 337.0 nm and after BC shifted to 335.0 and 334.0 nm, respectively. The surface hydrophobicity slightly increased after BC. In a solution of 8 M urea the lambdamax of BSA shifted to 346.4 and that of BSG to 342.5 nm. In contrast, in the same solution but after BC the lambdamax positions of HSA and HSG shifted to 355.9 and 357.7 nm, respectively. A decrease in fluorescence intensity, a shift in the maximum of emission, and an increase in surface hydrophobicity which reflected unfolding of proteins were observed. Here we provide evidence that the loosening of the HSP structure takes place primarily in various concentrations of urea before and after beer consumption. Differences in the fluorescence behavior of the proteins are attributed to disruption of the structure of proteins by denaturants as well as by the change in their compactability as a result of ethanol consumption.

Correlation between drug release kinetics from proteineous matrices and protein folding: elasticity and compressibility study

Naproxen sodium (NS) release mechanism from proteineous matrices based on egg albumin (EA) and bovine serum albumin (BSA) was investigated by several physico-chemical methods. The gel strength, modulus of elasticity and erosion properties of the matrices were studied and correlated with drug release kinetics. The results revealed that NS release rate from EA and BSA matrices was markedly different, indicating the significant role of protein nature and conformation on matrix behavior. Unexpectedly it was found that incorporation of NS to EA matrix increased gel strength and modulus of elasticity and decreased matrix erosion. This effect was dependent on NS concentration in the matrix. In contrast to EA, BSA behaved as a non-gelling matrix and was unable to retard drug release because of its high solubility. The influence of NS on protein folding and compressibility in protein solutions was studied using densitometric and ultrasonic techniques. Adiabatic compressibility measurements revealed that NS caused unfolding of EA, an effect which led to a decrease in EA intrinsic compressibility and the exposure of atomic side groups buried in protein interior. Unfolding of EA led to an increase of modulus of elasticity in solution (measured by ultrasonic velocimetry technique) which is in correlation with the modulus of elasticity measurements of gelled tablets (measured by Instron). In concentrated EA solutions, the results showed a large increase in EA compressibility and ultrasonic absorption in the presence of NS indicating a strong aggregation of the denatured state of EA. Regarding BSA, the results suggested that NS affected the packing of the protein interior, transforming it to a molten globule intermediate state, an effect that led to an increase in BSA compressibility. At high BSA concentrations, aggregation of the molten globule state was observed as indicated by an increase of BSA compressibility and ultrasonic absorption values.

Viscosity analysis of the temperature dependence of the solution conformation of ovalbumin

The viscosity of ovalbumin aqueous solutions was studied as a function of temperature and of protein concentration. Viscosity-temperature dependence was discussed on the basis of the modified Arrhenius formula at temperatures ranging from 5 to 55 degrees C. The activation energy of viscous flow for hydrated and unhydrated ovalbumin was calculated. Viscosity-concentration dependence, in turn, was discussed on the basis of Mooney equation. It has been shown that the shape parameter S decreases with increasing temperature, and self-crowding factor K does not depend on temperature. At low concentration limit the numerical values of the intrinsic viscosity and of Huggins coefficient were calculated. A master curve relating the specific viscosity etasp to the reduced concentration c[eta], over the whole range of temperature, was obtained and the three ranges of concentrations: diluted, semi-diluted and concentrated, are discussed. It has been proved that the Mark-Houvink-Kuhn-Sakurada (MHKS) exponent for ovalbumin does not depend on temperature.

Stability of some Cactaceae proteins based on fluorescence, circular dichroism, and differential scanning calorimetry measurements

Characterization of three cactus proteins (native and denatured) from Machaerocereus gummosus (Pitahaya agria), Lophocereu schottii (Garambullo), and Cholla opuntia (Cholla), was based on electrophoretic, fluorescence, CD (circular dichroism), DSC (differential scanning calorimetry), and FT-IR (Fourier transform infrared) measurements. The obtained results of intrinsic fluorescence, DSC, and CD were dissimilar for the three species of cactus, providing evidence of differences in secondary and tertiary structures. Cactus proteins may be situated in the following order corresponding to their relative stability: Machaerocereus gummosus (Pitahaya agria) > Cholla opuntia (Cholla) > Lophocereu schottii (Garambullo). Thermodynamic properties of proteins and their changes upon denaturation (temperature of denaturation, enthalphy, and the number of ruptured hydrogen bonds) were correlated with the secondary structure of proteins and disappearance of alpha-helix.

Elutability of Proteins from Aluminum-Containing Vaccine Adjuvants by Treatment with Surfactants

The elutability of proteins from adjuvants in model vaccines composed of ovalbumin adsorbed by aluminum hydroxide adjuvant or lysozyme adsorbed by aluminum phosphate adjuvant following treatment with surfactant solutions was studied. Nonionic (Triton X-100, lauryl maltoside), zwitterionic (lauryl sulfobetaine), anionic (sodium dodecyl sulfate), and cationic (cetylpyridinium chloride, dodecyltrimethylammonium chloride) surfactants were investigated. Cetylpyridinium chloride produced the greatest degree of elution (60%) of ovalbumin from aluminum hydroxide adjuvant. Sodium dodecyl sulfate completely eluted lysozyme from aluminum phosphate adjuvant. The effectiveness of surfactants in removing preadsorbed proteins was directly related to their ability to denature the protein. Micellar solubilization and electrostatic repulsion may also contribute to desorption. Copyright 1998 Academic Press. Copyright 1998Academic Press

Simultaneous differential scanning calorimetry, X-ray diffraction and FTIR spectrometry in studies of ovalbumin denaturation

The new application of differential scanning calorimetry (DSC) and the susceptibility of ovalbumin to alpha-chymotrypsin gave a quantitative estimation of protein denaturation in solid ovalbumin. Solid ovalbumin in granules with 11% of water was heated at 100 degrees C in closed and nonclosed ampules. In order to compare effects of size and crystal structure, two proteins (bovine albumin and gamma-globulin) were examined at similar conditions for the extent of denaturation. Ovalbumin and bovine albumin showed similar extents of denaturation, but gamma-globulin, with a very different molecular mass, showed the maximal conformational changes. The enthalpy of denaturation was measured to elucidate the conformational changes in solid proteins. Its value was used for calculation of the degree of denaturation. The thermodynamic data associated with transition were calculated and the number of bonds broken during denaturation was determined. Intrinsic fluorescence was utilized in order to compare these two methods. Moreover, X-ray diffraction and FTIR spectrometry were applied to native and denatured proteins.