The early stages of amyloid formation: biophysical and structural characterization of human calcitonin pre-fibrillar assemblies

Biophysical Properties of the Fibril Structure of the Toxic Conformer of Amyloid-β42: Characterization by Atomic Force Microscopy in Liquid and Molecular Docking

Alzheimer's disease is associated with the aggregation of the misfolded neuronal peptide, amyloid-β42 (Aβ42). Evidence has suggested that several reasons are responsible for the toxicity caused by the aggregation of Aβ42, including the conformational restriction of Aβ42. In this study, one of the toxic conformers of Aβ42, which contains a Glu-to-Pro substitution (E22P-Aβ42), was explored using atomic force microscopy and molecular docking to study the aggregation dynamics. We proposed a systematic model of fibril formation to better understand the molecular basis of conformational transitions in the Aβ42 species. Our results demonstrated the formation of amorphous aggregates in E22P-Aβ42 that are stem-based, network-like structures, while the formation of mature fibrils occurred in the less toxic conformer of Aβ42, E22-Aβ42, that are sphere-like flexible structures. A comparison was made between the biophysical properties of E22P-Aβ42 and E22-Aβ42 that revealed that E22P-Aβ42 had greater stiffness, dihedral angle, number of β sheets involved, and elasticity, compared with E22-Aβ42. These findings will have considerable implications toward our understanding of the structural basis of the toxicity caused by conformational diversity in Aβ42 species.

A review of the current research on in vivo and in vitro detection for alpha-synuclein: a biomarker of Parkinson's disease

Parkinson's disease is a health-threatening neurodegenerative disease of the elderly with clinical manifestations of motor and non-motor deficits such as tremor palsy and loss of smell. Alpha-synuclein (α-Syn) is the pathological basis of PD, it can abnormally aggregate into insoluble forms such as oligomers, fibrils, and plaques, causing degeneration of nigrostriatal dopaminergic neurons in the substantia nigra in the patient's brain and the formation of Lewy bodies (LBs) and Lewy neuritis (LN) inclusions. As a result, achieving α-Syn aggregate detection in the early stages of PD can effectively stop or delay the progression of the disease. In this paper, we provide a brief overview and analysis of the molecular structures and α-Syn in vivo and in vitro detection methods, such as mass spectrometry, antigen-antibody recognition, electrochemical sensors, and imaging techniques, intending to provide more technological support for detecting α-Syn early in the disease and intervening in the progression of Parkinson's disease.

Methods for the Characterization of Protein Aggregates

The physicochemical characterization of protein aggregates yields an important contribution to further our understanding on many diseases for which the formation of protein aggregates is one of the pathological hallmarks. On the other hand, bacterial inclusion bodies (IBs) have recently been shown to be highly pure proteinaceous aggregates of a few hundred nanometers, produced by recombinant bacteria supporting the biological activities of the embedded polypeptides. Despite the wide spectrum of uses of IBs as functional and biocompatible materials upon convenient engineering, very few is known about their physicochemical properties.In this chapter we present methods for the characterization of protein aggregates as particulate materials relevant to their physicochemical and nanoscale properties.Specifically, we describe the use of dynamic light scattering (DLS) for sizing, nanoparticle tracking analysis for sizing and counting, and zeta potential measurements for the determination of colloidal stability. To study the morphology of protein aggregates we present the use of atomic force microscopy (AFM) and scanning electron microscopy (SEM). Cryo-transmission electron microscopy (cryo-TEM) will be used for the determination of the internal structuration. Moreover, wettability and nanomechanical characterization can be performed using contact angle (CA) and force spectroscopic AFM (FS-AFM) measurements of the proteinaceous nanoparticles, respectively. Finally, the 4'4-dithiodipyridine (DTDP) method is presented as a way of relatively quantifying accessible sulfhydryl groups in the structure of the nanoparticle .The physical principles of the methods are briefly described and examples are given to help clarify capabilities of each technique.

Fibrillation of Human Calcitonin and Its Analogs: Effects of Phosphorylation and Disulfide Reduction

Some therapeutic peptides self-assemble in solution to form ordered, insoluble, β-sheet-rich amyloid fibrils. This physical instability can result in reduced potency, cause immunogenic side effects, and limit options for formulation. Understanding the mechanisms of fibrillation is key to developing rational mitigation strategies. Here, amide hydrogen-deuterium exchange with mass spectrometric analysis (HDX-MS) coupled with proteolytic digestion was used to identify the early stage interactions leading to fibrillation of human calcitonin (hCT), a peptide hormone important in calcium metabolism. hCT fibrillation kinetics was sigmoidal, with lag, growth, and plateau phases as shown by thioflavin T and turbidity measurements. HDX-MS of fibrillating hCT (pH 7.4; 25°C) suggested early involvement of the N-terminal (1-11) and central (12-19) fragments in interactions during the lag phase, whereas C-terminal fragments (20-32 and 26-32) showed limited involvement during this period. The residue-level information was used to develop phosphorylated hCT analogs that showed modified fibrillation that depended on phosphorylation site. Phosphorylation in the central region resulted in complete inhibition of fibrillation for the phospho-Thr-13 hCT analog, whereas phosphorylation in the N-terminal and C-terminal regions inhibited but did not prevent fibrillation. Reduction of the Cys1-Cys7 disulfide bond resulted in faster fibrillation with involvement of different hCT residues as indicated by pulsed HDX-MS. Together, the results demonstrate that small structural changes have significant effects on hCT fibrillation and that understanding these effects can inform the rational development of fibrillation-resistant hCT analogs.

Flavonoids with Vicinal Hydroxyl Groups Inhibit Human Calcitonin Amyloid Formation

Human calcitonin (hCT) is a 32-residue peptide hormone that can aggregate into amyloid fibrils and cause cellular toxicity. In this study, we investigated the inhibition effects of a group of polyphenolic molecules on hCT amyloid formation. Our results suggest that the gallate moiety in epigallocatechin-3-gallate (EGCG), a well-recognized amyloid inhibitor, is not critical for its inhibition function in the hCT amyloid formation. Our results demonstrate that flavonoid compounds, such as myricetin, quercetin, and baicalein, that contain vicinal hydroxyl groups on the phenyl ring effectively prevent hCT fibrillization. This structural feature may also be applied to non-flavonoid polyphenolic inhibitors. Moreover, our results indicate a plausible mechanistic role of these vicinal hydroxyl groups which might include the oxidation to form a quinone and the subsequent covalent linkage with amino acid residues such as lysine or histidine in hCT. This may further disrupt the crucial electrostatic and aromatic interactions involved in the process of hCT amyloid fibril formation. The inhibition activity of the polyphenolic compounds against hCT fibril formation may likely be attributed to a combination of factors such as covalent linkage formation, aromatic stacking, and hydrogen bonding interactions.

Complete aggregation pathway of amyloid β (1-40) and (1-42) resolved on an atomically clean interface

To visualize amyloid β (Aβ) aggregates requires an uncontaminated and artifact-free interface. This paper demonstrates the interface between graphene and pure water (verified to be atomically clean using tunneling microscopy) as an ideal platform for resolving size, shape, and morphology (measured by atomic force microscopy) of Aβ-40 and Aβ-42 peptide assemblies from 0.5 to 150 hours at a 5-hour time interval with single-particle resolution. After confirming faster aggregation of Aβ-42 in comparison to Aβ-40, a stable set of oligomers with a diameter distribution of ~7 to 9 nm was prevalently observed uniquely for Aβ-42 even after fibril appearance. The interaction energies between a distinct class of amyloid aggregates (dodecamers) and graphene was then quantified using molecular dynamics simulations. Last, differences in Aβ-40 and Aβ-42 networks were resolved, wherein only Aβ-42 fibrils were aligned through lateral interactions over micrometer-scale lengths, a property that could be exploited in the design of biofunctional materials.

Amyloid aggregates of the deubiquitinase OTUB1 are neurotoxic, suggesting that they contribute to the development of Parkinson's disease

Parkinson's disease (PD) is a multifactorial malady and the second most common neurodegenerative disorder, characterized by loss of dopaminergic neurons in the midbrain. A hallmark of PD pathology is the formation of intracellular protein inclusions, termed Lewy bodies (LBs). Recent MS studies have shown that OTU deubiquitinase ubiquitin aldehyde-binding 1 (OTUB1), a deubiquitinating enzyme of the OTU family, is enriched together with α-synuclein in LBs from individuals with PD and is also present in amyloid plaques associated with Alzheimer's disease. In the present study, using mammalian cell cultures and a PD mouse model, along with CD spectroscopy, atomic force microscopy, immunofluorescence-based imaging, and various biochemical assays, we demonstrate that after heat-induced protein aggregation, OTUB1 reacts strongly with both anti-A11 and anti-osteocalcin antibodies, detecting oligomeric, prefibrillar structures or fibrillar species of amyloidogenic proteins, respectively. Further, recombinant OTUB1 exhibited high thioflavin-T and Congo red binding and increased β-sheet formation upon heat induction. The oligomeric OTUB1 aggregates were highly cytotoxic, characteristic of many amyloid proteins. OTUB1 formed inclusions in neuronal cells and co-localized with thioflavin S and with α-synuclein during rotenone-induced stress. It also co-localized with the disease-associated variant pS129-α-synuclein in rotenone-exposed mouse brains. Interestingly, OTUB1 aggregates were also associated with severe cytoskeleton damage, rapid internalization inside the neuronal cells, and mitochondrial damage, all of which contribute to neurotoxicity. In conclusion, the results of our study indicate that OTUB1 may contribute to LB pathology through its amyloidogenic properties.

Effects of disulfide bond and cholesterol derivatives on human calcitonin amyloid formation

Human calcitonin (hCT) is a 32-residue peptide that aggregates to form amyloid fibrils under appropriate conditions. In this study, we investigated the effect of the intramolecular disulfide bond formed at the N-terminal region of the peptide in the aggregation kinetics of hCT. Our results indicate that the presence of the disulfide bond in hCT plays a crucial role in forming the critical nucleus needed for fibril formation, facilitating the rate of hCT amyloidogenesis. Furthermore, we reported for the first time the effects of cholesterol, cholesterol sulfate, and 3β-[N-(dimethylaminoethane)carbamoyl]-cholesterol (DC-cholesterol) on the amyloid formation of oxidized hCT. Our results show that while cholesterol does not affect amyloidogenesis of oxidized hCT, high concentrations of cholesterol sulfate exhibits a moderate inhibiting activity on hCT amyloid formation. In particular, our results show that DC-cholesterol strongly inhibits amyloidogenesis of oxidized hCT in a dose-dependent manner. Further studies at different pH conditions imply the crucial impact of electrostatic and hydrogen bonding interactions in mediating the interplay of hCT and the surface of DC-cholesterol vesicles and the inhibiting function of DC-cholesterol on hCT fibrillization.

Assembly Pathway Selection of Designer Self-Assembling Peptide and Fabrication of Hierarchical Scaffolds for Neural Regeneration

The self-assembling peptide (SAP) RADA 16-I has been modified with various functional motifs to improve its performances in biomedical applications. Nevertheless, the assembly mechanisms of designer functional RADA 16-I SAPs (F-SAPs) have not been clearly illustrated. The main problem is the difficulty in preparing a completely molecular aqueous solution of F-SAP. In the current study, we demonstrated that different procedures for preparing the F-SAP solution could result in the formation of different conformations and consequently micro/macroscopic morphologies. F-SAP was molecularly dissolved in an appropriate solvent, such as hexafluoroisopropanol (HFIP), as evidenced by random coil conformation characterized by circular dichroism spectroscopy and morphologies under transmission electron microscopy. The monomers were induced into monolayers when the F-SAP solution in HFIP was adsorbed on mica as observed by atomic force microscopy. However, nanoscaled filaments containing β-sheets dominated in the F-SAP aqueous solution, in which case water acted as a poor solvent of F-SAP. Furthermore, the results of molecular dynamics simulation implicated that water facilitated F-SAP aggregation, whereas HFIP inhibited it. The β-sheet assemblies formed in water exhibited a high kinetic stability and did not disassemble rapidly after the addition of HFIP. Our study indicated that selecting the right assembly pathway of F-SAP required for targeted functions, for example, delivery of hydrophobic drugs in aqueous conditions, could be achieved by optimizing the preparation protocol in addition to molecular design. Moreover, hierarchical scaffolds mimicking the natural extracellular matrix could be fabricated by the direct electrospinning of F-SAP molecular solution in HFIP and biodegradable polymer for applications in neural regeneration by promoting neural differentiation, neurite outgrowth, and synapse formation.

Growth-incompetent monomers of human calcitonin lead to a noncanonical direct relationship between peptide concentration and aggregation lag time

The role of the peptide hormone calcitonin in skeletal protection has led to its use as a therapeutic for osteoporosis. However, calcitonin aggregation into amyloid fibrils limits its therapeutic efficacy, necessitating a modification of calcitonin's aggregation kinetics. Here, we report a direct relationship between human calcitonin (hCT) concentration and aggregation lag time. This kinetic trend was contrary to the conventional understanding of amyloid aggregation and persisted over a range of aggregation conditions, as confirmed by thioflavin-T kinetics assays, CD spectroscopy, and transmission EM. Dynamic light scattering, 1H NMR experiments, and seeded thioflavin-T assay results indicated that differences in initial peptide species contribute to this trend more than variations in the primary nucleus formation rate. On the basis of kinetics modeling results, we propose a mechanism whereby a structural conversion of hCT monomers is needed before incorporation into the fibril. Our kinetic mechanism recapitulates the experimentally observed relationship between peptide concentration and lag time and represents a novel mechanism in amyloid aggregation. Interestingly, hCT at low pH and salmon calcitonin (sCT) exhibited the canonical inverse relationship between concentration and lag time. Comparative studies of hCT and sCT with molecular dynamics simulations and CD indicated an increased α-helical structure in sCT and low-pH hCT monomers compared with neutral-pH hCT, suggesting that α-helical monomers represent a growth-competent species, whereas unstructured random coil monomers represent a growth-incompetent species. Our finding that initial monomer concentration is positively correlated with lag time in hCT aggregation could help inform future efforts for improving therapeutic applications of CT.

Heme Stabilization of α-Synuclein Oligomers during Amyloid Fibril Formation

α-Synuclein (αSyn), which forms amyloid fibrils, is linked to the neuronal pathology of Parkinson's disease, as it is the major fibrillar component of Lewy bodies, the inclusions that are characteristic of the disease. Oligomeric structures, common to many neurodegenerative disease-related proteins, may in fact be the primary toxic species, while the amyloid fibrils exist either as a less toxic dead-end species or even as a beneficial mechanism for clearing damaged proteins. To alter the progression of the aggregation and gain insights into the prefibrillar structures, we determined the effect of heme on αSyn oligomerization by several different techniques, including native (nondenaturing) polyacrylamide gel electrophoresis, thioflavin T fluorescence, transmission electron microscopy, atomic force microscopy, circular dichroism, and membrane permeation using a calcein release assay. During aggregation, heme is able to bind the αSyn in a specific fashion, stabilizing distinct oligomeric conformations and promoting the formation of αSyn into annular structures, thereby delaying and/or inhibiting the fibrillation process. These results indicate that heme may play a regulatory role in the progression of Parkinson's disease; in addition, they provide insights into how the aggregation process may be altered, which may be applicable to the understanding of many neurodegenerative diseases.

Probing the role of aromatic residues in the self-assembly of Aβ(16-22) in fluorinated alcohols and their aqueous mixtures

The Aβ(16–22) sequence KLVFFAE spans the hydrophobic core of the Aβ peptide and plays an important role in its self-assembly. Apart from forming amyloid fibrils, Aβ(16–22) can self-associate into highly ordered nanotubes and ribbon-like structures depending on the composition of solvent used for dissolution. The Aβ(16–22) sequence which has FF at the 19th and 20th positions would be a good model to investigate peptide self-assembly in the context of aromatic interactions. In this study, self-assembly of Aβ(16–22) and its aromatic analogs obtained by replacement of F19, F20 or both by Y or W was examined after dissolution in fluorinated alcohols and their aqueous mixtures in solvent cluster forming conditions. The results indicate that the presence of aromatic residues Y and W and their position in the sequence plays an important role in self-assembly. We observe the formation of amyloid fibrils and other self-assembled structures such as spheres, rings and beads. Our results indicate that 20% HFIP is more favourable for amyloid fibril formation as compared to 20% TFE, when F is replaced with Y or W. The dissolution of peptides in DMSO followed by evaporation of solvent and dissolution in water appears to greatly influence peptide conformation, morphology and cross-β content of self-assembled structures. Our study shows that positioning of aromatic residues F, Y and W have an important role in directing self-assembly of the peptides.

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Effect of fluorinated alcohols on the aggregation of Aβ(16–22) and analogs was investigated.

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Replacement of F by Y and W in the Aβ(16–22) sequence modulates self-assembly.

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Positions of F, Y, W in Aβ(16–22) plays an important role in self-assembly.

Methods for characterization of protein aggregates

Physicochemical characterization of protein aggregates is important on one hand, due to its large impact in understanding many diseases for which formation of protein aggregates is one of the pathological hallmarks. On the other hand, recently it has been observed that bacterial inclusion bodies (IBs) are also highly pure proteinaceous aggregates of a few hundred nanometers produced by recombinant bacteria supporting the biological activities of the embedded polypeptides. From this fact arises a wide spectrum of uses of IBs as functional and biocompatible materials upon convenient engineering but very few is known about their physicochemical properties. In this chapter we present methods for the characterization of protein aggregates as particulate materials relevant to their physicochemical and nanoscale properties. Specifically, we describe the use of infrared spectroscopy (IR) for the determination of the secondary structure, dynamic light scattering (DLS) for sizing, nanosight for sizing and counting, and Z-potential measurements for the determination of colloidal stability. To study their morphology we present the use of atomic force microscopy (AFM). Cryo-transmission electron microscopy will be used for the determination of the internal structuration. Moreover, wettability and nanomechanical characterization can be performed using contact angle (CA) and force spectroscopic AFM measurements of the proteinaceous nanoparticles, respectively. The physical principles of the methods are briefly described and examples of data for real samples and how that data is interpreted are given to help clarify capabilities of each technique.

Characterization of the spherical intermediates and fibril formation of hCT in HEPES solution using solid-state 13C-NMR and transmission electron microscopy

Human calcitonin (hCT) is a 32-amino acid peptide hormone that contains an intrachain disulfide bridge between Cys1 and Cys7 and a proline amide at the C-terminus. hCT tends to associate to form a fibril precipitate of the same type as amyloid fibrils, and hence has been studied as a model of amyloid fibril formation. The fibrillation process in N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid (HEPES) solution was examined using transmission electron microscopy. The rate of hCT fibrillation in HEPES solution was much lower than in phosphate buffer and acetic acid solution. Spherical intermediate aggregates (nuclei) were observed during the early stage of fibril formation. Short proto-fibrils appeared on the surface of the spherical intermediates. Subsequently, the spherical intermediates transformed directly into long proto-fibrils, which then elongated into mature hCT fibrils. The fibrillation process was also examined using solid-state (13)C-NMR spectroscopy, which indicated that the fibril structure was a β-sheet in the central region and a mixture of random coils and β-sheets at the C-terminus. The kinetics of fibril formation was examined in terms of a two-step autocatalytic reaction mechanism. The first-step nucleation rate (k1) was lower in HEPES solution than in phosphate buffer and acetic acid solution because the half-life of the intermediates is significantly longer in HEPES solution. In contrast, the second-step fibril elongation rate (k2) was similar in HEPES solution and acidic solutions. Specific interaction of HEPES molecules with hCT may stabilize the spherical intermediates and consequently inhibit the fibril elongation process of hCT.

Implications of protein structure instability: from physiological to pathological secondary structure

Proteins are folded during their synthesis; this process may be spontaneous or assisted. Both phenomena are carefully regulated by the "housekeeping" mechanism and molecular chaperones to avoid the appearance of misfolded proteins. Unfolding process generally occurs during physiological degradation of protein, but in some specific cases it results from genetic or environmental changes and does not correspond to metabolic needs. The main outcome of these phenomena is the appearance of nonfunctional pathologically unfolded proteins with a strong tendency to aggregation. Moreover, for some of these unfolded proteins, the agglomeration that follows initial proteins association may give rise to highly structured soluble aggregates. These aggregates have been identified as the main cause of the so-called amyloidosis or amyloid diseases, such as Alzheimer's, Parkinson's, and Creutzfeldt-Jakob diseases, and type II diabetes mellitus. Although some common mechanisms of amyloid protein aggregation have been identified, the roles of the environmental conditions inducing amyloidosis remain to be clarified. In this review, we will summarize recent studies identifying the origin of amyloid nucleation and will try to predict the therapeutic prospects that may be opened by elucidation of the amyloidosis mechanisms.

Evaluation of Aβ fibrillization inhibitory effect by a PEG-peptide conjugate based on an Aβ peptide fragment with intramolecular FRET

A PEG-peptide conjugate based on an amyloid β peptide fragment was synthesized. The formed amyloid protofibril-like aggregates induced intramolecular FRET. It proved to be useful as a bioprobe to evaluate the inhibitory effect of organic molecules toward amyloid fibrillization.

Amyloid oligomer neurotoxicity, calcium dysregulation, and lipid rafts

Amyloid proteins constitute a chemically heterogeneous group of proteins, which share some biophysical and biological characteristics, the principal of which are the high propensity to acquire an incorrect folding and the tendency to aggregate. A number of diseases are associated with misfolding and aggregation of proteins, although only in some of them—most notably Alzheimer's disease (AD) and transmissible spongiform encephalopathies (TSEs)—a pathogenetic link with misfolded proteins is now widely recognized. Lipid rafts (LRs) have been involved in the pathophysiology of diseases associated with protein misfolding at several levels, including aggregation of misfolded proteins, amyloidogenic processing, and neurotoxicity. Among the pathogenic misfolded proteins, the AD-related protein amyloid β (Aβ) is by far the most studied protein, and a large body of evidence has been gathered on the role played by LRs in Aβ pathogenicity. However, significant amount of data has also been collected for several other amyloid proteins, so that their ability to interact with LRs can be considered an additional, shared feature characterizing the amyloid protein family. In this paper, we will review the evidence on the role of LRs in the neurotoxicity of huntingtin, α-synuclein, prion protein, and calcitonin.

Cholesterol in Alzheimer's disease and other amyloidogenic disorders

The complex association of cholesterol metabolism and Alzheimer's disease is presented in depth, including the possible benefits to be gained from cholesterol-lowering statin therapy. Then follows a survey of the role of neuronal membrane cholesterol in Abeta pore formation and Abeta fibrillogenesis, together with the link with membrane raft domains and gangliosides. The contribution of structural studies to Abeta fibrillogenesis, using TEM and AFM, is given some emphasis. The role of apolipoprotein E and its isoforms, in particular ApoE4, in cholesterol and Abeta binding is presented, in relation to genetic risk factors for Alzheimer's disease. Increasing evidence suggests that cholesterol oxidation products are of importance in generation of Alzheimer's disease, possibly induced by Abeta-produced hydrogen peroxide. The body of evidence for a link between cholesterol in atherosclerosis and Alzheimer's disease is increasing, along with an associated inflammatory response. The possible role of cholesterol in tau fibrillization, tauopathies and in some other non-Abeta amyloidogenic disorders is surveyed.

Effect of dehydration on the aggregation kinetics of two amyloid peptides

It is well-known that water plays a crucial role in the folding, dynamics, and function of proteins. Here we provide further evidence showing that the aggregation kinetics of peptides also depend strongly on their hydration status. Using reverse micelles as a tool to modulate the accessible number of water molecules and infrared spectroscopy and transmission electron microscopy as means to monitor aggregate formation, we show that the rate of aggregation of two amyloid forming peptides increases significantly under conditions where limited hydration of the peptide molecule is expected to occur. These results not only are in accord with recent computer simulations indicating that the expulsion of interfacial water molecules is a key event in the dimerization/oligmerization of amyloid beta (Abeta) peptides but also have implications for amyloid formation in vivo where molecular crowding is expected to influence the solvation status of proteins.

Annular structures as intermediates in fibril formation of Alzheimer Abeta17-42

We report all-atom molecular dynamics simulations of annular beta-amyloid (17-42) structures, single- and double-layered, in solution. We assess the structural stability and association force of Abeta annular oligomers associated through different interfaces, with a mutated sequence (M35A), and with the oxidation state (M35O). Simulation results show that single-layered annular models display inherent structural instability: one is broken down into linear-like oligomers, and the other collapses. On the other hand, a double-layered annular structure where the two layers interact through their C-termini to form an NC-CN interface (where N and C are the N and C termini, respectively) exhibits high structural stability over the simulation time due to strong hydrophobic interactions and geometrical constraints induced by the closed circular shape. The observed dimensions and molecular weight of the oligomers from atomic force microscopy (AFM) experiments are found to correspond well to our stable double-layered model with the NC-CN interface. Comparison with K3 annular structures derived from the beta 2-microglobulin suggests that the driving force for amyloid formation is sequence specific, strongly dependent on side-chain packing arrangements, structural morphologies, sequence composition, and residue positions. Combined with our previous simulations of linear-like Abeta, K3 peptide, and sup35-derived GNNQQNY peptide, the annular structures provide useful insight into oligomeric structures and driving forces that are critical in amyloid fibril formation.

Nanoimaging in protein-misfolding and -conformational diseases

Protein misfolding and the subsequent assembly of protein molecules into aggregates of various morphologies represent common mechanisms that link a number of important human diseases, known as protein-misfolding diseases. The current list of these disorders includes (but is not limited to) numerous neurodegenerative diseases, cataracts, arthritis, medullary carcinoma of the thyroid, late-onset diabetes mellitus, symptomatic (hemodialysis-related) beta(2)-microglobulin amyloidosis, arthritis and many other systemic, localized and familial amyloidoses. Progress in understanding protein-misfolding pathologies and in potential rational drug design aimed at the inhibition or reversal of protein aggregation depends on our ability to study the details of the misfolding process, to follow the aggregation process and to see and analyze the structure and mechanical properties of the aggregated particles. Nanoimaging provides a method to monitor the aggregation process, visualize protein aggregates and analyze their properties and provides fundamental knowledge of key factors that lead to protein misfolding and self-assembly in various protein-misfolding pathologies, therefore advancing medicine dramatically.