Amyloid fibril formation by peptide LYS (11-36) in aqueous trifluoroethanol

How the immune mousetrap works: Structural evidence for the immunomodulatory action of a peptide from influenza NS1 protein

One of the critical stages of the T-cell immune response is the dimerization of the intramembrane domains of T-cell receptors (TCR). Structural similarities between the immunosuppressive domains of viral proteins and the transmembrane domains of TCR have led several authors to hypothesize the mechanism of immune response suppression by highly pathogenic viruses: viral proteins embed themselves in the membrane and act on the intramembrane domain of the TCRalpha subunit, hindering its functional oligomerization. It has also been suggested that this mechanism is used by influenza A virus in NS1-mediated immunosuppression. We have shown that the peptide corresponding to the primary structure of the potential immunosuppressive domain of NS1 protein (G51) can reduce concanavalin A-induced proliferation of PBMC cells, as well as in vitro, G51 can affect the oligomerization of the core peptide corresponding to the intramembrane domain of TCR, using AFM and small-angle neutron scattering. The results obtained using in cellulo and in vitro model systems suggest the presence of functional interaction between the NS1 fragment and the intramembrane domain of the TCR alpha subunit. We have proposed a possible scheme for such interaction obtained by computer modeling. This suggests the existence of another NS1-mediated mechanism of immunosuppression in influenza.

Molecular simulation unravels the amyloidogenic misfolding of nascent ApoA1 protein, driven by deleterious point mutations occurring in between 170-178 hotspot region

Protein ApoA1 is extensively studied for its role in lipid metabolism. Its seedy dark side of amyloid formulation remains relatively understudied yet. Due to genetic mutations, the protein pathologically misshapes into its amyloid form that gets accumulated in various organs, including the heart. To contrive effective therapeutics against this debilitating congenital disorder, it is imperative to comprehend the structural ramifications induced by mutations in APoA1's dynamic conformation. Till now, several point mutations have been implicated in ApoA1's amyloidosis, although only a handful has been examined considerably. Especially, the single nucleotide polymorphisms (SNPs) that occur in-between 170-178 mutation hotspot site of APoA1 needs to be investigated, since most of them are culpable of amyloid deposition in the heart. To that effect, in the present study, we have computationally quantified and studied the ApoA1's biomolecular modifications fostered by SNPs in the 170-178 mutation hotspot. Findings from discrete molecular dynamics simulation studies indicate that the SNPs have noticeably steered the ApoA1's behaviour from its native structural dynamics. Analysis of protein's secondary structural changes exhibits a considerable change upon mutations. Further, subjecting the protein structures to simulated thermal denaturation shows increased resistance to denaturation among mutants when compared to native. Further, normal mode analysis of protein's dynamic motion also shows discrepancy in its dynamic structural change upon SNP. These structural digressions induced by SNPs can very well be the biomolecular incendiary that drives ApoA1 into its amyloidogenesis. And, understanding these structural modifications initiates a better understanding of SNP's amyloidogenic pathology on APoA1.Communicated by Ramaswamy H. Sarma.

Divergence Entropy-Based Evaluation of Hydrophobic Core in Aggressive and Resistant Forms of Transthyretin

The two forms of transthyretin differing slightly in the tertiary structure, despite the presence of five mutations, show radically different properties in terms of susceptibility to the amyloid transformation process. These two forms of transthyretin are the object of analysis. The search for the sources of these differences was carried out by means of a comparative analysis of the structure of these molecules in their native and early intermediate stage forms in the folding process. The criterion for assessing the degree of similarity and differences is the status of the hydrophobic core. The comparison of the level of arrangement of the hydrophobic core and its initial stages is possible thanks to the application of divergence entropy for the early intermediate stage and for the final forms. It was shown that the minimal differences observed in the structure of the hydrophobic core of the forms available in PDB, turned out to be significantly different in the early stage (ES) structure in folding process. The determined values of divergence entropy for both ES forms indicate the presence of the seed of hydrophobic core only in the form resistant to amyloid transformation. In the form of aggressively undergoing amyloid transformation, the structure lacking such a seed is revealed, being a stretched one with a high content of β-type structure. In the discussed case, the active presence of water in the structural transformation of proteins expressed in the fuzzy oil drop model (FOD) is of decisive importance for the generation of the final protein structure. It has been shown that the resistant form tends to generate a centric hydrophobic core with the possibility of creating a globular structure, i.e., a spherical micelle-like form. The aggressively transforming form reveals in the structure of its early intermediate, a tendency to form the ribbon-like micelle as observed in amyloid.

Lessons learned from protein aggregation: toward technological and biomedical applications

The close relationship between protein aggregation and neurodegenerative diseases has been the driving force behind the renewed interest in a field where biophysics, neurobiology and nanotechnology converge in the study of the aggregate state. On one hand, knowledge of the molecular principles that govern the processes of protein aggregation has a direct impact on the design of new drugs for high-incidence pathologies that currently can only be treated palliatively. On the other hand, exploiting the benefits of protein aggregation in the design of new nanomaterials could have a strong impact on biotechnology. Here we review the contributions of our research group on novel neuroprotective strategies developed using a purely biophysical approach. First, we examine how doxycycline, a well-known and innocuous antibiotic, can reshape α-synuclein oligomers into non-toxic high-molecular-weight species with decreased ability to destabilize biological membranes, affect cell viability and form additional toxic species. This mechanism can be exploited to diminish the toxicity of α-synuclein oligomers in Parkinson's disease. Second, we discuss a novel function in proteostasis for extracellular glyceraldehyde 3-phosphate dehydrogenase (GAPDH) in combination with a specific glycosaminoglycan (GAG) present in the extracellular matrix. GAPDH, by changing its quaternary structure from a tetramer to protofibrillar assembly, can kidnap toxic species of α-synuclein, and thereby interfere with the spreading of the disease. Finally, we review a brighter side of protein aggregation, that of exploiting the physicochemical advantages of amyloid aggregates as nanomaterials. For this, we designed a new generation of insoluble biocatalysts based on the binding of photo-immobilized enzymes onto hybrid protein:GAG amyloid nanofibrils. These new nanomaterials can be easily functionalized by attaching different enzymes through dityrosine covalent bonds.

Bottom-Up Synthesis and Sensor Applications of Biomimetic Nanostructures

The combination of nanotechnology, biology, and bioengineering greatly improved the developments of nanomaterials with unique functions and properties. Biomolecules as the nanoscale building blocks play very important roles for the final formation of functional nanostructures. Many kinds of novel nanostructures have been created by using the bioinspired self-assembly and subsequent binding with various nanoparticles. In this review, we summarized the studies on the fabrications and sensor applications of biomimetic nanostructures. The strategies for creating different bottom-up nanostructures by using biomolecules like DNA, protein, peptide, and virus, as well as microorganisms like bacteria and plant leaf are introduced. In addition, the potential applications of the synthesized biomimetic nanostructures for colorimetry, fluorescence, surface plasmon resonance, surface-enhanced Raman scattering, electrical resistance, electrochemistry, and quartz crystal microbalance sensors are presented. This review will promote the understanding of relationships between biomolecules/microorganisms and functional nanomaterials in one way, and in another way it will guide the design and synthesis of biomimetic nanomaterials with unique properties in the future.

Towards efficient biocatalysts: photo-immobilization of a lipase on novel lysozyme amyloid-like nanofibrils

Photoimmobilization of enzymes on an amyloid-like fibrillar scaffold.

The Amyloid Fibril-Forming Properties of the Amphibian Antimicrobial Peptide Uperin 3.5

The amphibian skin is a vast resource for bioactive peptides, which form the basis of the animals' innate immune system. Key components of the secretions of the cutaneous glands are antimicrobial peptides (AMPs), which exert their cytotoxic effects often as a result of membrane disruption. It is becoming increasingly evident that there is a link between the mechanism of action of AMPs and amyloidogenic peptides and proteins. In this work, we demonstrate that the broad-spectrum amphibian AMP uperin 3.5, which has a random-coil structure in solution but adopts an α-helical structure in membrane-like environments, forms amyloid fibrils rapidly in solution at neutral pH. These fibrils are cytotoxic to model neuronal cells in a similar fashion to those formed by the proteins implicated in neurodegenerative diseases. The addition of small quantities of 2,2,2-trifluoroethanol accelerates fibril formation by uperin 3.5, and is correlated with a structural stabilisation induced by this co-solvent. Uperin 3.5 fibril formation and the associated cellular toxicity are inhibited by the polyphenol (-)-epigallocatechin-3-gallate (EGCG). Furthermore, EGCG rapidly dissociates fully formed uperin 3.5 fibrils. Ion mobility-mass spectrometry reveals that uperin 3.5 adopts various oligomeric states in solution. Combined, these observations imply that the mechanism of membrane permeability by uperin 3.5 is related to its fibril-forming properties.

Comparing and correlating solubility parameters governing the self-assembly of molecular gels using 1,3:2,4-dibenzylidene sorbitol as the gelator

Solvent properties play a central role in mediating the aggregation and self-assembly of molecular gelators and their growth into fibers. Numerous attempts have been made to correlate the solubility parameters of solvents and gelation abilities of molecular gelators, but a comprehensive comparison of the most important parameters has yet to appear. Here, the degree to which partition coefficients (log P), Henry's law constants (HLC), dipole moments, static relative permittivities (ε(r)), solvatochromic E(T)(30) parameters, Kamlet-Taft parameters (β, α, and π), Catalan's solvatochromic parameters (SPP, SB, and SA), Hildebrand solubility parameters (δ(i)), and Hansen solubility parameters (δ(p), δ(d), δ(h)) and the associated Hansen distance (R(ij)) of 62 solvents (covering a wide range of properties) can be correlated with the self-assembly and gelation of 1,3:2,4-dibenzylidene sorbitol (DBS) gelation, a classic molecular gelator, is assessed systematically. The approach presented describes the basis for each of the parameters and how it can be applied. As such, it is an instructional blueprint for how to assess the appropriate type of solvent parameter for use with other molecular gelators as well as with molecules forming other types of self-assembled materials. The results also reveal several important insights into the factors favoring the gelation of solvents by DBS. The ability of a solvent to accept or donate a hydrogen bond is much more important than solvent polarity in determining whether mixtures with DBS become solutions, clear gels, or opaque gels. Thermodynamically derived parameters could not be correlated to the physical properties of the molecular gels unless they were dissected into their individual HSPs. The DBS solvent phases tend to cluster in regions of Hansen space and are highly influenced by the hydrogen-bonding HSP, δ(h). It is also found that the fate of this molecular gelator, unlike that of polymers, is influenced not only by the magnitude of the distance between the HSPs for DBS and the HSPs of the solvent, R(ij), but also by the directionality of R(ij): if the solvent has a larger hydrogen-bonding HSP (indicating stronger H-bonding) than that of the DBS, then clear gels are formed; opaque gels form when the solvent has a lower δ(h) than does DBS.

Interplay between desolvation and secondary structure in mediating cosolvent and temperature induced alpha-synuclein aggregation

Both increased temperature and moderate concentrations of fluorinated alcohols enhance aggregation of the Parkinson's disease-associated protein α-synuclein (αS). Here, we investigate the secondary structural rearrangements induced by heating and trifluoroethanol [TFE]. At low TFE concentrations, CD spectra feature a negative peak characteristic of disordered polypeptides near 200 nm and a slight shoulder around 220 nm suggesting some polyproline-II content. Upon heating, these peaks weaken, while a weak negative signal develops at 222 nm. At high TFE concentrations, the spectra show distinct minima at 208 and 222 nm, indicative of considerable α-helical structure, which diminish upon heating. We observe a crossover between the low-TFE and high-TFE behavior near 15% TFE, where we previously showed that a partially helical intermediate is populated. We postulate that the protein is well solvated by water at low TFE concentrations and by TFE at high TFE concentrations, but may become desolvated at the crossover point. We discuss the potential roles and interplay of desolvation and helical secondary structure in driving αS aggregation.

A desolvation model for trifluoroethanol-induced aggregation of enhanced green fluorescent protein

Studies of amyloid disease-associated proteins in aqueous solutions containing 2,2,2-trifluoroethanol (TFE) have shown that the formation of structural intermediates is often correlated with enhanced protein aggregation. Here, enhanced green fluorescent protein (EGFP) is used as a model protein system to investigate the causal relationship between TFE-induced structural transitions and aggregation. Using circular dichroism spectroscopy, light scattering measurements, and transmission electron microscopy imaging, we demonstrate that population of a partially α-helical, monomeric intermediate is roughly correlated with the growth of β-sheet-rich, flexible fibrils for acid-denatured EGFP. By fitting our circular dichroism data to a model in which TFE-water mixtures are assumed to be ideal solutions, we show that increasing entropic costs of protein solvation in TFE-water mixtures may both cause the population of the intermediate state and increase aggregate production. Tertiary structure and electrostatic repulsion also impede aggregation. We conclude that initiation of EGFP aggregation in TFE likely involves overcoming of multiple protective factors, rather than stabilization of aggregation-prone structural elements.

Modulation of pathway of insulin fibrillation by a small molecule helix inducer 2,2,2-trifluoroethanol

Many proteins form ordered irreversible structural aggregates called amyloid fibrils, which are associated with numerous neurodegenerative diseases. Insulin, a largely α-helical protein associated with type II diabetes, self-assembles to form amyloid fibrils in vitro. Insulin fibrillation goes through a number of intermediate phases that includes a soluble oligomeric phase believed to be the most toxic phase. Small molecules may play a very important role in modulating the fibrillation pathways. It is possible to induce and stabilize helix structures in proteins by a fluorinated alcohol 2,2,2-trifluoro ethanol (TFE). Since fibrillation process of many proteins is associated with conversion of α-helical structures into β-sheet configuration, we thought it would be interesting to study the effect of TFE on the fibrillation of insulin. In absence of TFE, soluble protofibrillar oligomeric intermediates formed directly from the insulin trimer. The protofibrillar aggregates transformed into mature fibrils over time. We demonstrated that although TFE did not prevent the appearance of matured amyloid fibrils, it prevented the appearance of soluble aggregates of insulin. TFE converted the insulin trimer into monomers and fibril formation proceeded from the monomeric state in a cooperative way avoiding the soluble oligomeric phase. At 25% TFE, distinct morphological changes resulting in more discrete fibrils were visible. The effect of the small molecule TFE on the avoidance of the formation soluble oligomeric state during fibrillation may have considerable implications in reducing cellular toxicity.

Existence of metastable intermediate lysozyme conformation highlights the role of alcohols in altering protein stability

Alcohols have a manifold effect on the conformational and thermodynamic stability of native proteins. Here, we study the effect of moderate concentrations of trifluoroethanol (TFE) on the thermal stability of hen egg-white lysozyme (HEWL), by far-UV circular dichroism and by steady-state and time-resolved photoluminescence of intrinsic tryptophans. Our results highlight that TFE affects lysozyme stability by preferential solvation of the protein molecule. Furthermore, we discovered the existence at 20% TFE of an equilibrium partially folded state of lysozyme, intermediate between the native and the unfolded state. A three-state model is therefore used to interpolate the thermal denaturation data. Our analysis explains how the stabilization of the intermediate conformation enhances the entropic contribution to unfolding, and thus decreases the unfolding temperature, while, at the same time, TFE enhances the conformational stability of the native fold at room temperature. Eventually, we challenged the ability of these intermediate structures to form supramolecular aggregates by heating experiments at different TFE concentrations.

Effects of disulfide bond formation and protein helicity on the aggregation of activating transcription factor 5

Amorphous aggregation is a major problem for protein biopharmaceuticals, and aggregate formation in a drug formulation can have serious health implications for the patient. In many cases, an immunogenic response is generated from the administration of a drug product containing aggregated protein. This becomes especially significant when the patient requires long-term or repeated administration of the drug, because the likelihood of a severe immune response increases. While the prevention of protein aggregation is critically important for the future of protein pharmaceuticals, the mechanism of amorphous aggregation is still poorly understood. The lack of understanding regarding nonfibrillar aggregation is largely due to the fact that assembly is difficult to study. In particular the role that various structural features (i.e., alpha-helix, beta-structure, disulfide bonds) play in the aggregation process varies with the amino acid sequence and is dependent upon tertiary structure and solution conditions. Well-structured proteins do not readily aggregate in solution, whereas partially unfolded proteins tend to aggregate rapidly and often become insoluble. Here, we present a unique and simple system for studying amorphous protein aggregation. We have previously reported the isolation of the basic leucine zipper (bZIP) domain of activating transcription factor 5 (ATF5), a protein notable for its potential as a pharmaceutical target for treatment of glioblastoma multiforme. This domain consists of a single alpha-helix and possesses a single cysteine residue. It is only partially structured and displays marginal stability in solution under physiological conditions. We have modulated solution conditions that affect backbone solubility and the oxidation state of the thiol to successfully investigate the role that alpha-helical structure and disulfide bond formation play in protein stability. Our data indicate that covalent cross-linking helps to retain ATF5's helicity, which inhibits the formation of large aggregates. These studies have led to the identification of stabilizing conditions for ATF5, which will enable further study of the protein as a pharmaceutical target. Moreover, this work has general implications for analyzing stability of helical proteins in vitro as well as the specific atomic-level interactions in ATF5 that contribute to instability and self-association.

A critical assessment of the role of helical intermediates in amyloid formation by natively unfolded proteins and polypeptides

Amyloidogenic proteins and polypeptides can be divided into two structural classes, namely those which are flexible and are intrinsically disordered in their unaggregated state and those which form a compact globular structure with a well-defined tertiary fold in their normally soluble state. This review article is focused on amyloid formation by natively disordered polypeptides. Important examples of this class include islet amyloid polypeptide (IAPP, amylin), pro-IAPP processing intermediates, alpha-synuclein, the Abeta peptide, atrial natriuretic factor, calcitonin, pro-calcitonin, the medin polypeptide, as well as a range of de novo designed peptides. Amyloid formation is a complex process consisting of a lag phase during which no detectable fibril material is formed, followed by a rapid growth phase that leads to amyloid fibrils. A critical analysis of the literature suggests that a subset of intrinsically disordered polypeptides populate a helical intermediate during the lag phase. In this scenario, early formation of multimeric species is promoted by helix-helix association involving one region of the polypeptide chain which leads to a high effective concentration of an amyloidogenic sequence located in a different region of the chain. Helical intermediates appear to be particularly important in membrane-catalyzed amyloid formation and have been implicated in glycosaminoglycan mediated amyloid formation as well. There is suggestive evidence that targeting helix-helix interactions can be a viable strategy to inhibit amyloid formation. The characterization of transient helical intermediates is challenging, but new methods are being developed that offer the prospect of providing residue-specific information in real time.

Gas-phase behavior of noncovalent transmembrane segment complexes

Specific helix oligomerization between transmembrane segments (TMSs) is often promoted by motifs like GxxxG. Disruption of this motif in the transmembrane segments of vesicular stomatitis virus G-protein and of glycophorin A results in a reduced dimerization level studied by in vivo systems like ToxR. This paper reports the influence of sequence motifs like GxxxG in solution and the gas phase.The transmembrane segments may behave differently in the gas and liquid phase, because of the absence of surrounding solvent molecules in the gas phase. Comparison of experiments depending on peptide properties performed in the gas and liquid phase discloses that the peptides retain 'some memory' of their liquid-phase structure in the gas phase. A direct correlation has been found between helicity in solution as determined by circular dichroism and dimerization in the gas phase monitored by electrospray mass spectrometry. These results show that a proper folding in solution is required for oligomerization.On the other hand, sequence-specific oligomerization depending on the GxxxG motif was not observed with the mass spectrometric detection. Further on, neither concentration-dependent complex studies nor studies regarding complex stability in the gas phase - via collision-induced dissociation (CID) - led to sequence-specific differences.Finally, the findings show that in mass spectrometric measurements noncovalent interactions of studied TMSs is rather more dependent on the secondary structure and proper folding than on their primary structure.

Hen egg white lysozyme fibrillation: a deep-UV resonance Raman spectroscopic study

Amyloid fibrils are associated with numerous degenerative diseases. The molecular mechanism of the structural transformation of native protein to the highly ordered cross-beta structure, the key feature of amyloid fibrils, is under active investigation. Conventional biophysical methods have limited application in addressing the problem because of the heterogeneous nature of the system. In this study, we demonstrated that deep-UV resonance Raman (DUVRR) spectroscopy in combination with circular dichroism (CD) and intrinsic tryptophan fluorescence allowed for quantitative characterization of protein structural evolution at all stages of hen egg white lysozyme fibrillation in vitro. DUVRR spectroscopy was found to be complimentary to the far-UV CD because it is (i) more sensitive to beta -sheet than to alpha -helix, and (ii) capable of characterizing quantitatively inhomogeneous and highly light-scattering samples. In addition, phenylalanine, a natural DUVRR spectroscopic biomarker of protein structural rearrangements, exhibited substantial changes in the Raman cross section of the 1000-cm(-1) band at various stages of fibrillation.

Engineering the oil binding capacity and crystallinity of self-assembled fibrillar networks of in edible oils

The crystallinity and oil binding capacity of 12-hydroxystearic acid (12HSA)-vegetable oil organogels was modified by changing the post-crystallization annealing temperature from 5 °C to 30 °C for 24 h. The gels stored at 5 °C had a highly branched crystalline structure with small uniform pores, as determined by cryo-scanning electron microscopy. Large T2proton relaxation peaks at 50 to 70 ms determined by pulse nuclear magnetic resonance (pNMR) suggested the presence of highly immobilized oil at 5 °C. When the gels were stored at 30 °C, longer fibers and a less branched network were observed. At 30 °C, the 12HSA network's crystallinity was enhanced with fewer inclusions of liquid oil as determined by pNMR. When the gels were stored at 30 °C, a significantly shorter T2 relaxation peak was observed. The increased crystallinity, at 30 °C, was attributed to a reduction in bulk supersaturation, resulting in a very high crystallographic mismatch nucleation barrier (ΔG*) which favored one-dimensional fiber growth. However, at a lower crystallization temperature of 5 °C, there is an increase in the supersaturation and hence the crystallographic mismatch barrier is significantly lower, increasing fiber tip branching. The nucleation-growth-branching-growth model for self-assembled fibrillar networks explains the differences in crystallinity, pore size and oil syneresis observed for the 12HSA-vegetable oil organogels. It was found that the gels stored at 30 °C syneresised 1.35 times faster than the gels stored at 5 °C. Furthermore, the change in the T2 relaxations and the ratio of the complex viscosity/pore radius were 1.35 and 1.30 respectively.

Interactions of trifluroethanol with the Trp-cage peptide

It has been suggested that aggregation of fluorinated alcohols in water solutions is involved with the abilities of these alcohols to provoke conformational changes in peptides and proteins. The extent of fluoroalcohol aggregation depends on the degree of fluorination: hexafluoroisopropanol (HFIP) is more extensively aggregated than is TFE. We previously described a study of the interactions of HFIP with the peptide Trp-cage and provided evidence for the formation of long-lived complexes between this fluoroalcohol and the peptide. In the present work, we have examined the interactions of the less-fluorinated TFE with Trp-cage, in order to probe the role of fluoroalcohol aggregation in the phenomena observed. Intermolecular (1)H{(19)F} nuclear Overhauser effects arising from interactions of TFE with the hydrogens of the peptide in a solution containing 42% TFE were determined at sample temperatures from 5 to 45 degrees C. It is shown that the folded state of the peptide under these conditions is essentially the same as that observed in water and in 30% HFIP-water. The observed peptide-solvent NOEs indicate formation of complexes of Trp-cage with TFE that persist for times of the order of 1 ns. The interactions leading to complexes with TFE are somewhat weaker than those involved in complex formation with HFIP. There are no indications that the aggregation of fluoroalcohol is a necessary concomitant of the interactions of TFE or HFIP with Trp-cage. Rather, the stronger and more long-lived interactions of HFIP with Trp-cage appear to be primarily the result of the greater hydrogen-bonding ability and hydrophobicity of this fluoroalcohol.

A quasi-spontaneous amyloid route in a DNA binding gene regulatory domain: The papillomavirus HPV16 E2 protein

The DNA binding domain of papillomavirus E2 proteins is at the center of the regulation of gene transcription and replication of the virus. Its unique fold consists of a beta-barrel domain that combines an eight-stranded dimeric beta-barrel core interface with two symmetrical DNA binding alpha-helices and other two helices, packed against the central barrel. Treatment with low amounts of trifluoroethanol readily leads to a mostly beta-sheet oligomeric species, with a loss of near-UV circular dichroism signal and increase in its ANS binding capacity, indicating that buried hydrophobic surfaces become accessible to the solvent. This species subsequently undergoes a slow transition into amyloid aggregates as determined by light scattering and Congo red and thioflavin T binding. Electron microscopy shows short amyloid fibers with a curly aspect as the end product. The amyloid route is completely prevented by addition of stoichiometrical amounts of specific DNA, strongly suggesting that unfolding of the DNA binding alpha-helix is required for the formation of the intermediate. The slow nature of this expanded beta-oligomeric species and the availability of several different conformational probes make it an excellent model for investigating amyloid mechanisms. The mild perturbation required for entering an amyloid route is indicative of a preexisting equilibrium. Oligomerization processes are required for the assembly of transcription initiation and DNA replication machineries, where proteins from different viruses must come together with host cell proteins. The E2 protein is a virus-encoded multifunctional master regulator that may exert one of its multiple functions through its ability to oligomerize.

Interactions of lysozyme in guanidinium chloride solutions from static and dynamic light-scattering measurements

The interactions of partially unfolded proteins provide insight into protein folding and protein aggregation. In this work, we studied partially unfolded hen egg lysozyme interactions in solutions containing up to 7 M guanidinium chloride (GdnHCl). The osmotic second virial coefficient (B(22)) of lysozyme was measured using static light scattering in GdnHCl aqueous solutions at 20 degrees C and pH 4.5. B(22) is positive in all solutions, indicating repulsive protein-protein interactions. At low GdnHCl concentrations, B(22) decreases with rising ionic strength: in the absence of GdnHCl, B(22) is 1.1 x 10(-3) mLmol/g(2), decreasing to 3.0 x 10(-5) mLmol/g(2) in the presence of 1 M GdnHCl. Lysozyme unfolds in solutions at GdnHCl concentrations higher than 3 M. Under such conditions, B(22) increases with ionic strength, reaching 8.0 x 10(-4) mLmol/g(2) at 6.5 M GdnHCl. Protein-protein hydrodynamic interactions were evaluated from concentration-dependent diffusivity measurements, obtained from dynamic light scattering. At moderate GdnHCl concentrations, lysozyme interparticle interactions are least repulsive and hydrodynamic interactions are least attractive. The lysozyme hydrodynamic radius was calculated from infinite-dilution diffusivity and did not change significantly during protein unfolding. Our results contribute toward better understanding of protein interactions of partially unfolded states in the presence of a denaturant; they may be helpful for the design of protein refolding processes that avoid protein aggregation.