Protein misfolding and aggregation: Mechanism, factors and detection

Tailoring the Molecular Structure of 6-Gingerol for Targeting the Phase Separation in Human Lysozyme

Human lysozyme undergoes a phase-separation process to form insoluble amyloid-architects that cause several pathologies including systemic amyloidosis. Here we have tailored 6-gingerol by extending its molecular framework with active functional groups to specifically target lysozyme phase-transition events. Aggregation assay revealed that tailored 6-gingerol with 4-aromatic moieties (MTV4) substantially suppressed the conversion of the lysozyme low-density liquid phase (LDLP) to solid-phase structured amyloids. The data obtained from biophysical, computational, and microscopic imaging tools suggest direct intervention of MTV4 with the liquid-liquid phase separation. The CD data suggest that MTV4 was able to retain the native conformation of lysozyme. Both biomolecular and computational data reveal the interference of MTV4 with the aggregation-prone hydrophobic stretches within the lysozyme, thereby retaining the native structure and reversing the misfolded intermediates to active monomers. Also, MTV4 was able to induce rapid dissolution of preformed-toxic amyloid fibrils. These results reinforce the importance of the aromatic-aromatic interaction in preventing human lysozyme phase separation.

Inhibition of insulin fibrillation by carboxyphenylboronic acid-modified chitosan oligosaccharide based on electrostatic interactions and hydrophobic interactions

A novel inhibitor, carboxyphenylboronic acid-modified chitosan oligosaccharide (COS-CPBA), was developed by coupling carboxyphenylboronic acid (CPBA) with chitosan oligosaccharide (COS) to inhibit insulin fibrillation. Extensive biophysical assays indicated that COS-CPBA could decelerate insulin aggregation, hinder the conformational transition from α-helix to β-sheet structure, change the morphology of insulin aggregates and alter fibrillation pathway. A mechanism for the inhibition of insulin fibrillation by COS-CPBA was proposed. It considers that insulin molecules bind to COS-CPBA via hydrophobic interactions, while the positively charged groups in COS-CPBA exert electrostatic repulsion on the bound insulin molecules. These two opposite forces cause the insulin molecules to display extended conformations and hinder the conformational transition of insulin from α-helix to β-sheet structure necessary for fibrillation, thus decelerating aggregation and altering the fibrillation pathway of insulin. The studies provide novel ideas for the development of more effective inhibitors of amyloid fibrillation.

Stability of Protein Pharmaceuticals: Recent Advances

There have been significant advances in the formulation and stabilization of proteins in the liquid state over the past years since our previous review. Our mechanistic understanding of protein-excipient interactions has increased, allowing one to develop formulations in a more rational fashion. The field has moved towards more complex and challenging formulations, such as high concentration formulations to allow for subcutaneous administration and co-formulation. While much of the published work has focused on mAbs, the principles appear to apply to any therapeutic protein, although mAbs clearly have some distinctive features. In this review, we first discuss chemical degradation reactions. This is followed by a section on physical instability issues. Then, more specific topics are addressed: instability induced by interactions with interfaces, predictive methods for physical stability and interplay between chemical and physical instability. The final parts are devoted to discussions how all the above impacts (co-)formulation strategies, in particular for high protein concentration solutions.'

Protonation-State Dependent Modulation of Hen Egg-White Lysozyme Fibrillation under the Influence of a Short Synthetic Peptide

Under the influence of various conditions, misfolding of soluble proteins occurs, leading to the formation of toxic insoluble amyloids. The formation and deposition of such amyloids within the body are associated with detrimental biological consequences such as the onset of several amyloid-related diseases. Previously, we established a strategy for the rational design of peptide inhibitors against amyloid formation based on the amyloidogenic-prone region of the protein. In the current study, we have designed and identified an Asp-containing rationally designed hexapeptide (SqP4) as an excellent inhibitor of hen egg-white lysozyme (HEWL) amyloid progression in vitro. First, SqP4 showed strong affinity toward the native monomeric HEWL leading to the stabilization of the native form and restriction in the unfolding process of monomeric HEWL. Second, SqP4 was found to arrest the amyloidogenic misfolded structure of HEWL in a nonfibrillar monomer-like stage. We also observed the differential effect of the protonation state of the charged amino acid (Asp) within the peptide inhibitor on the amyloid formation of HEWL and explored the reason behind the observations. The findings of this study can be implemented in future strategies for the development of potent therapeutics against other amyloid-related diseases.

Probing protein aggregation through spectroscopic insights and multimodal approaches: A comprehensive review for counteracting neurodegenerative disorders

Aberrant accumulation of protein misfolding can cause aggregation and fibrillation and is one of the primary characteristic features of neurodegenerative diseases. Because they are disordered, misfolded, and aggregated proteins pose a significant setback in drug designing. The structural study of intermediate steps in these kinds of aggregated proteins will allow us to determine the conformational changes as well as the probable pathways encompassing various neurodegenerative disorders. The analysis of protein aggregates involved in neurodegenerative diseases relies on a diverse toolkit of biophysical techniques, encompassing both morphological and non-morphological methods. Additionally, Thioflavin T (ThT) assays and Circular Dichroism (CD) spectroscopy facilitate investigations into aggregation kinetics and secondary structure alterations. The collective application of these biophysical techniques empowers researchers to comprehensively unravel the intricate nature of protein aggregates associated with neurodegeneration. Furthermore, the topics covered in this review have summed up a handful of well-established techniques used for the structural analysis of protein aggregation. This multifaceted approach advances our fundamental understanding of the underlying mechanisms driving neurodegenerative diseases and informs potential therapeutic strategies.

Pathways of amyloid fibril formation and protein aggregation

The main cause of many neurodegenerative diseases and systemic amyloidoses is protein and peptide aggregation and the formation of amyloid fibrils. The study of aggregation mechanisms, the discovery and description of aggregate structures, and a comprehensive understanding of the molecular mechanisms of amyloid formation are of great importance for the diagnostic processes at the molecular level and for the development of therapeutic strategies to counter aggregation-associated disorders. Given that understanding protein misfolding phenomena is directly related to the protein folding process, we will briefly explain the protein folding mechanism and then discuss the important factors involved in protein aggregation. In the following, we review different mechanisms of amyloid formation and finally represent the current knowledge on how amyloid fibrils are formed based on kinetic and thermodynamic factors.

Each big journey starts with a first step: Importance of oligomerization

Protein oligomers, widely found in nature, have significant physiological and pathological functions. They are classified into three groups based on their function and toxicity. Significant advancements are being achieved in the development of functional oligomers, with a focus on various applications and their engineering. The antimicrobial peptides oligomers play roles in death of bacterial and cancer cells. The predominant pathogenic species in neurodegenerative disorders, as shown by recent results, are amyloid oligomers, which are the main subject of this chapter. They are generated throughout the aggregation process, serving as both intermediates in the subsequent aggregation pathways and ultimate products. Some of them may possess potent cytotoxic properties and through diverse mechanisms cause cellular impairment, and ultimately, the death of cells and disease progression. Information regarding their structure, formation mechanism, and toxicity is limited due to their inherent instability and structural variability. This chapter aims to provide a concise overview of the current knowledge regarding amyloid oligomers.

Formation of rice protein fibrils is highly sensitive to the different types of metal ions: Aggregation behavior and possible mechanisms

The effects of Ca2+, Cu2+, and Fe3+ on rice protein (RP) fibril formation were investigated in this study. Low Ca2+ concentration (≤150 mM) moderately unfolded the conformation of RP, promoting the exposure of hydrophobic sites and RP fibril assembly. Fibril formation was especially promoted with earlier addition of Ca2+. Cu2+ and Fe3+ inhibited RP fibril formation in a dose-dependent manner, and the inhibitory effect of Fe3+ was stronger due to higher affinity with RP. Additionally, the addition of Cu2+ and Fe3+ reduced α-helix and β-sheet contents of RP, respectively, hindering the formation of stacked β-sheet, the main internal structure of fibrils. These two ions also resulted in the formation of random aggregates within 15-50 nm, which further inhibited the conversion of proteins to fibrils. Moreover, Cu2+ and Fe3+ prevented the recruitment of nucleus into fibril-growth-sites, and formed fibrils were disrupted into fragments when these ions were added.

Aβ42 fibril and non-fibril oligomers characterization using a nanopipette

The Aβ42 aggregates with different structures and morphology was investigated through a single molecule label-free technique. To this end, the quartz nanopipettes were functionalized with polyethylene glycol. The set of Aβ42- epigallocatechin-3-gallate fibrils with length (from 85 nm to 250 nm) obtained by sonication was detected. The comparison of experimental and computed value of the amplitude of relative current blockade using a geometrical model show that for fibrils longer than 80 nm, the discriminating parameter is their diameter. Then, non-fibril oligomers obtain from Aβ42(Osaka) aggregation at different time seed was investigated. The analysis of the amplitude of relative current blockade shows that detected oligomers are smaller than 30 nm regardless the aggregation time. In addition, the wide distributions of the dwell time suggests the polymorph character of the sample.

A comprehensive review of protein misfolding disorders, underlying mechanism, clinical diagnosis, and therapeutic strategies

INTRODUCTION

Proteins are the most common biological macromolecules in living system and are building blocks of life. They are extremely dynamic in structure and functions. Due to several modifications, proteins undergo misfolding, leading to aggregation and thereby developing neurodegenerative and systemic diseases. Understanding the pathology of these diseases and the techniques used to diagnose them is therefore crucial for their effective management . There are several techniques, currently being in use to diagnose them and those will be discussed in this review.

AIM/OBJECTIVES

Current review aims to discuss an overview of protein aggregation and the underlying mechanisms linked to neurodegeneration and systemic diseases. Also, the review highlights protein misfolding disorders, their clinical diagnosis, and treatment strategies.

METHODOLOGY

Literature related to neurodegenerative and systemic diseases was explored through PubMed, Google Scholar, Scopus, and Medline databases. The keywords used for literature survey and analysis are protein aggregation, neurodegenerative disorders, Alzheimer's disease, Parkinson's disease, systemic diseases, protein aggregation mechanisms, etc. DISCUSSION /CONCLUSION: This review summarises the pathogenesis of neurodegenerative and systemic disorders caused by protein misfolding and aggregation. The clinical diagnosis and therapeutic strategies adopted for the management of these diseases are also discussed to aid in a better understanding of protein misfolding disorders. Many significant concerns about the role, characteristics, and consequences of protein aggregates in neurodegenerative and systemic diseases are not clearly understood to date. Regardless of technological advancements, there are still great difficulties in the management and cure of these diseases. Therefore, for better understanding, diagnosis, and treatment of neurodegenerative and systemic diseases, more studies to identify novel drugs that may aid in their treatment and management are required.

Chemical Modification of the Amino Groups of Human Insulin: Investigating Structural Properties and Amorphous Aggregation of Acetylated Species

The efficacy of human recombinant insulin can be affected by its aggregation. Effects of acetylation were observed on insulin structure, stability, and aggregation at 37 and 50 °C and pH of 5.0 and 7.4 with the use of spectroscopy, circular dichroism (CD), dynamic light scattering (DLS), and atomic force microscopy (AFM). Raman and FTIR results were indicative of structural changes in AC-INS, and CD analyses showed a slight increase in β-sheet content in AC-INS. Melting temperature (T_m) measurements indicated an overall more stable structure and spectroscopic assessment showed a more compact one. Formation of amorphous aggregates was followed over time and kinetics parameters showed a longer nucleation phase (higher t* amount) and lower aggregates amount (lower A_lim) for acetylated insulin (AC-INS) compared to native (N-INS) in all tested conditions. The results of amyloid-specific probes approved the formation of amorphous aggregates. Size particle and microscopic analysis suggested that AC-INS was less prone to form aggregates, which were smaller if formed. In conclusion, this study has demonstrated that controlled acetylation of insulin may lead to its higher stability and lower propensity toward amorphous aggregation and has provided insight into the result of this type of post-translational protein modification.

Elucidating the inhibitory effects of rationally designed novel hexapeptide against hen egg white lysozyme fibrillation at acidic and physiological pH

Inhibition of highly ordered cross-β-sheet-rich aggregates of misfolded amyloid proteins using rationally designed sequence-based short peptides is a promising therapeutic strategy for the treatment of neurodegenerative diseases. Here, we have explored the anti-amyloidogenic potency of a rationally designed hexapeptide (Tyr-Pro-Gln-Ile-Pro-Asn) on in vitro hen egg white lysozyme (HEWL) amyloid fibril formation at acidic pH and physiological pH using computational docking as well as various biophysical techniques such as fluorescence spectroscopy, UV-vis spectroscopy, FTIR spectroscopy, confocal microscopy and TEM. The peptide was designed based on the aggregation-prone region (APR) of HEWL and thus referred to as SqP1 (Sequence-based Peptide 1). SqP1 showed over 70% inhibition of HEWL amyloid formation at pH 2.2 and approximately 50% inhibition at pH 7.5. We propose that SqP1 binds to the APR of HEWL and interacts strongly with the Trp62/Trp63, ultimately stabilizing monomeric HEWL at both the pH conditions and preventing conformation changes in the structure of HEWL, leading to the formation of amyloidogenic fibrillar structures. A sequence-based peptide inhibitor of HEWL amyloid formation was not reported previously, making this a critical study that will further emphasize the importance of short synthetic peptides as amyloid inhibitors.

Evaluating the inhibitory potential of natural compound luteolin on human lysozyme fibrillation

Numerous pathophysiological conditions known as amyloidosis, have been connected to protein misfolding leading to aggregation of proteins. Inhibition of cytotoxic aggregates or disaggregation of the preformed fibrils is thus one of the important strategies in the prevention of such diseases. Growing interest and exploration of identification of small molecules mainly natural compounds can prevent or delay amyloid fibril formation. We examined the mechanism of interaction and inhibition of human lysozyme (HL) aggregates with luteolin (LT). Biophysical and computational approaches have been employed to study the effect of LT on HL amyloid aggregation. Transmission Electronic Microscopy, Thioflavin T fluorescence, UV-vis spectroscopy, and RLS demonstrates that LT inhibit HL fibril formation. ANS fluorescence and hemolytic assay was also employed to examine the effect of the LT on toxicity of HL aggregation. Docking and molecular dynamics results showed that LT interacted with HL via hydrophobic and hydrogen interactions, thus reducing fibrillation levels. These findings highlight the benefit of polyphenols as safe therapy for preventing amyloid related diseases.

Protein Misfolding and Aggregation in Proteinopathies: Causes, Mechanism and Cellular Response

Proteins are central to life functions. Alterations in the structure of proteins are reflected in their function. Misfolded proteins and their aggregates present a significant risk to the cell. Cells have a diverse but integrated network of protection mechanisms. Streams of misfolded proteins that cells are continuously exposed to must be continually monitored by an elaborated network of molecular chaperones and protein degradation factors to control and contain protein misfolding problems. Aggregation inhibition properties of small molecules such as polyphenols are important as they possess other beneficial properties such as antioxidative, anti-inflammatory, and pro-autophagic properties and help neuroprotection. A candidate with such desired features is important for any possible treatment development for protein aggregation diseases. There is a need to study the protein misfolding phenomenon so that we can treat some of the worst kinds of human ailments related to protein misfolding and aggregation.

A Polymorphism in the Gene Encoding Heat Shock Factor 1 (HSF1) Increases the Risk of Type 2 Diabetes: A Pilot Study Supports a Role for Impaired Protein Folding in Disease Pathogenesis

The aim of this pilot study was to investigate whether polymorphisms in the gene encoding heat shock factor 1 (HSF1), a transcriptional activator of molecular chaperones, play a role in the development of type 2 diabetes (T2D). A total of 3229 unrelated individuals of Slavic origin, including 1569 T2D patients and 1660 age- and sex-matched healthy controls, were enrolled for the study. Five common single nucleotide polymorphisms (SNPs) of the HSF1 gene were genotyped using the MassArray-4 system. SNPs rs7838717 (p = 0.002) and rs3757971 (p = 0.005) showed an association with an increased risk of T2D in females with a body mass index ≥ 25 kg/m². The rs7838717T-rs4279640T-rs3757971C and rs7838717T-rs4279640T-rs3757971T haplotypes were associated with increased and decreased disease risk in overweight or obese females, respectively. The associations were replicated as disease susceptibility genes in large cohorts from the UK Biobank (p = 0.008), DIAMANTE (p = 2.7 × 10^-13), and DIAGRAM (p = 0.0004) consortiums. The functional annotation of the SNPs revealed that the rs7838717-T and rs3757971C alleles correlated with increased expression of the genes involved in unfolded protein response. The present study showed, for the first time, that genetic variation of HSF1 is associated with the risk of type 2 diabetes, supporting a role for impaired protein folding in disease pathogenesis.

Chickpea Peptide: A Nutraceutical Molecule Corroborating Neurodegenerative and ACE-I Inhibition

Chickpea seeds are the source of proteins in human nutrition and attribute some nutraceutical properties. Herein, we report the effects of chickpea seed bioactive peptide on albumin, insulin, lactoglobulin and lysozyme amyloid fibril formation. Employing thioflavin T (ThT) assays and circular dichroism (CD), amyloid structural binding transition was experimented to analyze the inhibition of amyloid fibril formation. The purified active peptide with a molecular mass of 934.53 Da was evaluated in vitro for its ACE-I inhibitory, antibacterial, antifungal and antidiabetic activities. Further, in vivo animal studies were carried out in wistar rats for blood pressure lowering action. In hypertensive rats, chickpea peptide decreased 131 ± 3.57 mm of Hg for systolic blood pressure and 86 ± 1.5 mm of Hg for diastolic blood pressure after 8 h intraperitoneal administration. Additionally, the peptide suppressed the fibrillation of amyloid and destabilized the preformed mature fibrils. Data emphasize efficacy of chickpea peptide vis-a-vis ACE-Inhibitory, antibacterial, antifungal, antidiabetic and anti-amyloidogenic activities, allowing us to propose this novel peptide as a suitable candidate for nutraceutical-based drugs and seems the first kind of its nature.

Quantitative Structural Proteomics Unveils the Conformational Changes of Proteins under the Endoplasmic Reticulum Stress

Protein structures are decisive for their activities and interactions with other molecules. Global analysis of protein structures and conformational changes cannot be achieved by commonly used abundance-based proteomics. Here, we integrated cysteine covalent labeling, selective enrichment, and quantitative proteomics to study protein structures and structural changes on a large scale. This method was applied to globally investigate protein structures in HEK293T cells and protein structural changes in the cells with the tunicamycin (Tm)-induced endoplasmic reticulum (ER) stress. We quantified several thousand cysteine residues, which contain unprecedented and valuable information of protein structures. Combining this method with pulsed stable isotope labeling by amino acids in cell culture, we further analyzed the folding state differences between pre-existing and newly synthesized proteins in cells under the Tm treatment. Besides newly synthesized proteins, unexpectedly, many pre-existing proteins were found to become unfolded upon ER stress, especially those related to gene transcription and protein translation. Furthermore, the current results reveal that N-glycosylation plays a more important role in the folding process of the tertiary and quaternary structures than the secondary structures for newly synthesized proteins. Considering the importance of cysteine in protein structures, this method can be extensively applied in the biological and biomedical research fields.

Virus-like Particles: Fundamentals and Biomedical Applications

Nanotechnology is a fast-evolving field focused on fabricating nanoscale objects for industrial, cosmetic, and therapeutic applications. Virus-like particles (VLPs) are self-assembled nanoparticles whose intrinsic properties, such as heterogeneity, and highly ordered structural organization are exploited to prepare vaccines; imaging agents; construct nanobioreactors; cancer treatment approaches; or deliver drugs, genes, and enzymes. However, depending upon the intrinsic features of the native virus from which they are produced, the therapeutic performance of VLPs can vary. This review compiles the recent scientific literature about the fundamentals of VLPs with biomedical applications. We consulted different databases to present a general scenario about viruses and how VLPs are produced in eukaryotic and prokaryotic cell lines to entrap therapeutic cargo. Moreover, the structural classification, morphology, and methods to functionalize the surface of VLPs are discussed. Finally, different characterization techniques required to examine the size, charge, aggregation, and composition of VLPs are described.

Cucurbit[7]uril Macrocyclic Sensors for Optical Fingerprinting: Predicting Protein Structural Changes to Identifying Disease-Specific Amyloid Assemblies

In a three-dimensional (3D) representation, each protein molecule displays a specific pattern of chemical and topological features, which are altered during its misfolding and aggregation pathway. Generating a recognizable fingerprint from such features could provide an enticing approach not only to identify these biomolecules but also to gain clues regarding their folding state and the occurrence of pathologically lethal misfolded aggregates. We report here a universal strategy to generate a fluorescent fingerprint from biomolecules by employing the pan-selective molecular recognition feature of a cucurbit[7]uril (CB[7]) macrocyclic receptor. We implemented a direct sensing strategy by covalently tethering CB[7] with a library of fluorescent reporters. When CB[7] recognizes the chemical and geometrical features of a biomolecule, it brings the tethered fluorophore into the vicinity, concomitantly reporting the nature of its binding microenvironment through a change in their optical signature. The photophysical properties of the fluorophores allow a multitude of probing modes, while their structural features provide additional binding diversity, generating a distinct fluorescence fingerprint from the biomolecule. We first used this strategy to rapidly discriminate a diverse range of protein analytes. The macrocyclic sensor was then applied to probe conformational changes in the protein structure and identify the formation of oligomeric and fibrillar species from misfolded proteins. Notably, the sensor system allowed us to differentiate between different self-assembled forms of the disease-specific amyloid-β (Aβ) aggregates and segregated them from other generic amyloid structures with a 100% identification accuracy. Ultimately, this sensor system predicted clinically relevant changes by fingerprinting serum samples from a cohort of pregnant women.

Identification of a Steric Zipper Motif in the Amyloidogenic Core of Human Cystatin C and Its Use for the Design of Self-Assembling Peptides

Amyloid fibrils have been known for many years. Unfortunately, their fame stems from negative aspects related to amyloid diseases. Nevertheless, due to their properties, they can be used as interesting nanomaterials. Apart from their remarkable stability, amyloid fibrils may be regarded as a kind of a storage medium and as a source of active peptides. In many cases, their structure may guarantee a controlled and slow release of peptides in their active form; therefore, they can be used as a potential nanomaterial in drug delivery systems. In addition, amyloid fibrils display controllable stiffness, flexibility, and satisfactory mechanical strength. In addition, they can be modified and functionalized very easily. Understanding the structure and genesis of amyloid assemblies derived from a broad range of amyloidogenic proteins could help to better understand and use this unique material. One of the factors responsible for amyloid aggregation is the steric zipper. Here, we report the discovery of steric zipper-forming peptides in the sequence of the amyloidogenic protein, human cystatin C (HCC). The ability of short peptides derived from this fragment of HCC to form fibrillar structures with defined self-association characteristics and the factors influencing this aggregation are also presented in this paper.

The inhibitory effects of natural antioxidants on protein glycation as well as aggregation induced by methylglyoxal and underlying mechanisms

The non-enzymatic glycation of protein can result in the formation of advanced glycation end-products (AGEs), leading to the deposition of amyloid proteins, and it's essential for the pathogenesis of diabetes complications and amyloid diseases. Reactive dicarbonyl compounds, such as methylglyoxal (MGO), are one of the most reactive glycating agents. Therefore, it's crucially necessary to inhibit protein glycation and aggregation induced by MGO. In the present study, we aimed to systemically investigate the anti-glycation and anti-fibrillization activities of eight natural antioxidants, including apigenin, quercetin (Que), catechin, resveratrol (Res), and gallic acid (GA), L-ascorbic acid (L-AA), limonene, and β-carotene, during MGO-induced protein glycation and aggregation. Furthermore, the underlying mechanisms were clarified. The formation of AGEs and the degree of protein aggregation were characterized by optical detection, flow cytometry, and so on. The results demonstrated that eight selected natural antioxidants could inhibit glycation and protein aggregation induced by MGO via the synergy of scavenging free radicals, capturing MGO, and interacting with proteins, among which GA (300 μM) and Res (15 μM) had higher inhibition rates on both argpyrimidine (specific fluorescent AGEs, 17% and 22%, respectively) and protein amyloid aggregation (42% and 29%, respectively). These findings suggested that antioxidants could act as potential inhibitors of AGEs and glycation-induced protein aggregation, which were expected to become a new strategy for the prevention and treatment of diabetes and amyloid diseases. Besides, these inhibition mechanisms provided valuable insights into the design and development of candidate drugs for the prevention and treatment of AGEs and protein aggregation-related diseases.

Amyloid Protein-Biofunctionalized Polydopamine Nanoparticles Demonstrate Minimal Plasma Protein Fouling and Efficient Photothermal Therapy

Polydopamine (PDA) shows great application potential in photothermal therapy (PTT) of tumors due to its excellent photothermal performance. However, PDA rich in a large number of catechin structures, with strong adhesion, can readily attach to plasma proteins in blood to form protein corona, which greatly hinders the transfer efficiency to tumors and reduces the bioavailability. In this paper, a simple, rapid phase-transitioned albumin biomimetic nanocorona (TBSA) is used for the surface camouflage of PDA nanoparticles for minimal plasma protein fouling and efficient PTT. TBSA coating is formed by the BSA-derived amyloid through the hydrophobic aggregation near the isoelectric point and the rupture of disulfide bonds by tris(2-carboxyethyl) phosphine. The stable PDA@TBSA complexes are formed by camouflaging TBSA onto the surface of PDA through hydrophobic, electrostatic, and covalent binding between TBSA and PDA, which showed excellent anti-plasma protein adsorption properties profited from the surface charge of PDA@TBSA approaching equilibrium and the surface passivation of BSA. The plasma protein thickness of the PDA@TBSA surface is 6 times lower than that of PDA at adsorption saturation. In vitro and in vivo experiments have revealed that PDA@TBSA has an excellent photothermal antitumor effect compared to PDA. Both PDA and PDA@TBSA treatment plus 808 nm laser irradiation result in more than 70% inhibition on tumor cell proliferation. In addition, PDA@TBSA does not cause a significant inflammatory response and tissue damage. Taken together, the TBSA coating endows PDA with low-fouling functions in blood and improves the residence time of PDA in blood and enrichment in the tumor tissue. This work offers a novel and efficient strategy for the design of functional nanosystems exploiting the speciality of the biomolecular corona formation around nanomaterials.

Myeloperoxidase-induced fibrinogen unfolding and clotting

Due to its unique properties and high biomedical relevance fibrinogen is a promising protein for the development of various matrixes and scaffolds for biotechnological applications. Fibrinogen molecules may form extensive clots either upon specific cleavage by thrombin or in thrombin-free environment, for example, in the presence of different salts. Here, we report the novel type of non-conventional fibrinogen clot formation, which is mediated by myeloperoxidase and takes place even at low fibrinogen concentrations (<0.1 mg/ml). We have revealed fibrillar nature of myeloperoxidase-mediated fibrinogen clots, which differ morphologically from fibrin clots. We have shown that fibrinogen clotting is mediated by direct interaction of myeloperoxidase molecules with the outer globular regions of fibrinogen molecules followed by fibrinogen unfolding from its natural trinodular to a fibrillar structure. We have demonstrated a major role of the Debye screening effect in regulating of myeloperoxidase-induced fibrinogen clotting, which is facilitated by small ionic strength. While fibrinogen in an aqueous solution with myeloperoxidase undergoes changes, the enzymatic activity of myeloperoxidase is not inhibited in excess of fibrinogen. The obtained results open new insights into fibrinogen clotting, give new possibilities for the development of fibrinogen-based functional biomaterials, and provide the novel concepts of protein unfolding.

Combined action of chemical chaperones on stability, aggregation and oligomeric state of muscle glycogen phosphorylase b

Chemical chaperones are a class of small molecules, which enhance protein stability, folding, inhibit protein aggregation, and are used for long-term storage of therapeutic proteins. The combined action of chemical chaperones trehalose, betaine and lysine on stability, aggregation and oligomeric state of muscle glycogen phosphorylase b (Phb) has been studied. Dynamic light scattering data indicate that the affinity of trehalose to Phb increased in the presence of betaine or lysine at both stages (stage of nucleation and aggregate growth) of enzyme aggregation at 48 °C, in contrast, the affinity of betaine to the enzyme in the presence of lysine remained practically unchanged. According to differential scanning calorimetry and analytical ultracentrifugation data, the mixture of trehalose and betaine stabilized Phb stronger than either of them in total. Moreover, the destabilizing effect of lysine on the enzyme was almost completely compensated by trehalose and only partially by betaine. The main protective effect of the mixtures of osmolytes and lysine is associated with their influence on the dissociation/denaturation stage, which is the rate-limiting one of Phb aggregation. Thus, a pair of chaperones affects the stability, oligomeric state, and aggregation of Phb differently than individual chaperones.

Spectroscopic studies on the stability and nucleation-independent fibrillation of partially-unfolded proteins in crowded environment

Fibril formation of globular proteins is driven by attaining an appropriate partially-unfolded conformation. Excluded volume effect exerted by the presence of other macromolecules in the solution, as found in the cellular interior, might affect the conformational state of proteins and alter their fibril formation process. The change in structure, stability and rate of fibril formation of aggregation-prone partially-unfolded states of lysozyme (Lyz) and α-lactalbumin (ALA) in the presence of different sizes of polyethylene glycol (PEG) is examined using spectroscopic methods. Thermal denaturation and far-UV CD studies suggest that Lyz is stabilized by PEGs and the stability increases with increasing concentration of PEGs. However, the stability of ALA depends on the size and concentration of PEG. The change in enthalpy of unfolding indicates the existence of soft-interactions between the proteins and PEG along with excluded volume effect. Fibrillation rate of Lyz is not significantly altered in the presence of lower concentrations of PEGs suggesting that the crowding effect dominates the viscosity-induced retardation of protein association whereas at higher concentrations the rates are reduced. In case of ALA, the rate of fibrillation is drastically reduced; however, there is a marginal increase with the increasing concentration of PEG. The results suggest that the fibril formation is influenced by change in initial conformation of the partially-unfolded states of the proteins and their stability in the presence of the crowding agent. Further, the size and concentration of the crowding agent, and the soft-interaction between the proteins and PEG also affects the fibrillation.

Novel metabolic enzyme inhibitors designed through the molecular hybridization of thiazole and pyrazoline scaffolds

New hybrid thiazolyl-pyrazoline derivatives (4a-k) were obtained through a facile and versatile synthetic procedure, and their inhibitory effects on the human carbonic anhydrase (hCA) isoforms I and II as well as on acetylcholinesterase (AChE) were determined. All new thiazolyl-pyrazolines showed activity at nanomolar levels as hCA I, hCA II, and AChE inhibitors, with K_I values in the range of 13.35-63.79, 7.01-115.80, and 17.89-48.05 nM, respectively. 1-[4-(4-Cyanophenyl)thiazol-2-yl]-3-(4-piperidinophenyl)-5-(4-fluorophenyl)-2-pyrazoline (4f) and 1-(4-phenylthiazol-2-yl)-3-(4-piperidinophenyl)-5-(4-fluorophenyl)-2-pyrazoline (4a) against hCAs and 1-[4-(4-chlorophenyl)thiazol-2-yl]-3-(4-piperidinophenyl)-5-(4-fluorophenyl)-2-pyrazoline (4d) and 1-[4-(4-nitrophenyl)thiazol-2-yl]-3-(4-piperidinophenyl)-5-(4-fluorophenyl)-2-pyrazoline (4b) against AChE were identified as highly potent inhibitors, superior to the standard drugs, acetazolamide and tacrine, respectively. Compounds 4a-k were also evaluated for their cytotoxic effects on the L929 mouse fibroblast (normal) cell line. Moreover, a comprehensive ligand-receptor interaction prediction was performed using the ADME-Tox, Glide XP, and MM-GBSA modules of the Schrödinger Small-Molecule Drug Discovery Suite to elucidate the potential binding modes of the new hybrid inhibitors against these metabolic enzymes.

Autoxidation Enhances Anti-Amyloid Potential of Flavone Derivatives

The increasing prevalence of amyloid-related disorders, such as Alzheimer's or Parkinson's disease, raises the need for effective anti-amyloid drugs. It has been shown on numerous occasions that flavones, a group of naturally occurring anti-oxidants, can impact the aggregation process of several amyloidogenic proteins and peptides, including amyloid-beta. Due to flavone autoxidation at neutral pH, it is uncertain if the effective inhibitor is the initial molecule or a product of this reaction, as many anti-amyloid assays attempt to mimic physiological conditions. In this work, we examine the aggregation-inhibiting properties of flavones before and after they are oxidized. The oxidation of flavones was monitored by measuring the UV-vis absorbance spectrum change over time. The protein aggregation kinetics were followed by measuring the amyloidophilic dye thioflavin-T (ThT) fluorescence intensity change. Atomic force microscopy was employed to image the aggregates formed with the most prominent inhibitors. We demonstrate that flavones, which undergo autoxidation, have a far greater potency at inhibiting the aggregation of both the disease-related amyloid-beta, as well as a model amyloidogenic protein-insulin. Oxidized 6,2',3'-trihydroxyflavone was the most potent inhibitor affecting both insulin (7-fold inhibition) and amyloid-beta (2-fold inhibition). We also show that this tendency to autoxidize is related to the positions of the flavone hydroxyl groups.

Chemical stabilization of γ-polyglutamate by chitosan and the effect of co-solvents on the stability

In protein-based formulations, conformational distortions and attractive interactions may cause insoluble and undesired aggregates. In the case of ionic peptides, including cationic or anionic, commonly electrostatic interactions are the main factors that control structure assembling. In this study, it was proposed that grafting of chitosan (CS) to γ-polyglutamic acid (γ-PGA) might exhibit much strong inhibiting effect on the formation of protein aggregates due to multiple amino groups and hydrophilic properties. To guarantee stable and safe biopharmaceutical formulation, the potency of a variety of stabilizers including sugars (glucose, sucrose), polyols (sorbitol, glycerol), surfactant (Tween 20), salting-out salt (PBS), and also different pH values have been evaluated on stabilizing or destabilizing the native state of CS-g-PGA copolymer using FTIR, CD, DLS, and SDS-PAGE. The comparable analysis revealed that the stability of CS-g-PGA was strongly dependent on pH owing to the polyelectrolyte characteristics of the polymers. Altogether these results implied that CS at optimized conditions might be an important precursor for the pharmaceutical industry and function as a new polymer for aggregation suppression and protein stabilization.

Rational Biological Interface Engineering: Amyloidal Supramolecular Microstructure-Inspired Hydrogel

Amyloidal proteins, which are prone to form fibrillar and ordered aggregates in vivo and in vitro, underlie the mechanism for neurodegenerative disorders and also play essential functions in the process of life. Amyloid fibrils typically adopt a distinctive β-sheet structure, which renders them with inherent extracellular matrix (ECM)-mimicking properties, such as powerful mechanical strength, promising adhesion, and antibacterial activity. Additionally, amyloidal proteins are a category of programmable self-assembled macromolecules, and their assembly and consequent nanostructure can be manipulated rationally. The above advantages motivate researchers to investigate the potential of amyloidal proteins as a novel type of hydrogel material. Currently, the amyloid-inspired hydrogel has become an emerging area and has been widely applied in a variety of biomedical fields, such as tissue repair, cell scaffolds, and drug delivery. In this review, we focus on the discussion of molecular mechanisms underlying the hydrogenation of amyloidal proteins, and introduce the advances achieved in biomedical applications of amyloid-inspired hydrogels.

Size-based Degradation of Therapeutic Proteins - Mechanisms, Modelling and Control

Protein therapeutics are in great demand due to their effectiveness towards hard-to-treat diseases. Despite their high demand, these bio-therapeutics are very susceptible to degradation via aggregation, fragmentation, oxidation, and reduction, all of which are very likely to affect the quality and efficacy of the product. Mechanisms and modelling of these degradation (aggregation and fragmentation) pathways is critical for gaining a deeper understanding of stability of these products. This review aims to provide a summary of major developments that have occurred towards unravelling the mechanisms of size-based protein degradation (particularly aggregation and fragmentation), modelling of these size-based degradation pathways, and their control. Major caveats that remain in our understanding and control of size-based protein degradation have also been presented and discussed.

The albumin-based nanoparticle formation in relation to protein aggregation

Albumin is an attractive protein for the preparation of nanoparticle with possible therapeutic applications, due to its biodegradable, nontoxic, non-immunogenic, and metabolizable properties. Many studies have investigated the formation of albumin nanoparticles, generally by the desolvation or coacervation approaches. One of the most important parameters that should be considered in the formation of nanoparticles is their morphology (size and shape). There are many proposals to control the nanoparticle size, but it remains a challenge for researchers yet. In this study, we showed that control of BSA-based nanoparticles/microparticles size could be achieved by varying the temperature and pH and therefore controlling the rate of aggregation. The aggregation behavior was monitored by UV-Vis spectroscopy, SEM, and dye-binding assay. Our results provide more options for the size and shape control of BSA-based nanoparticle in natural buffer systems. The aggregation of BSA at different temperatures within the range of 50-80 °C were studied under the effect of different pHs in the range of 4.7-6.2. In this research, we found that protein aggregation under extreme conditions of pH and temperature, or at the pH near to pI appears to be amorphous, and at the pH above the pI seems to be the amyloid fibril structure. In some instances where the aggregation is neither too fast nor too slow, in the initial phase of the aggregation process, nanoparticle structures can be identified and separated by mechanistic approaches. This observation suggests that the best condition for monitoring the formation of albumin-based nanoparticles could be pH 5.7, 70 °C. Satisfactory rationalization of all aspects of our experimental observation requires further and more detailed study.

The effects of nanobubbles on the assembly of glucagon amyloid fibrils

Some recent studies have shown that the surface and interface play an important role in the assembly and aggregation of amyloid proteins. However, it is unclear how the gas-liquid interface affects the protein assembly at the nanometer scale although the presence of gas-liquid interfaces is very common in in vitro experiments. Nanobubbles have a large specific surface area, which provides a stage for interactions with various proteins and peptides on the nanometer scale. In this work, nanobubbles produced in solution were employed for studying the effects of the gas-liquid interface on the assembly of glucagon proteins. Atomic force microscopy (AFM) studies showed that nanobubble-treated glucagon solution formed fibrils with an apparent height of 4.02 ± 0.71 nm, in contrast to the fibrils formed with a height of 2.14 ± 0.53 nm in the control. Transmission electron microscopy (TEM) results also showed that nanobubbles promoted the assembly of glucagon to form more fibrils. Thioflavin T (ThT) fluorescence and Fourier transform infrared (FTIR) analyses indicated that the nanobubbles induced the change of the glucagon conformation to a β-sheet structure. A mechanism that explains how nanobubbles affect the assembly of glucagon amyloid fibrils was proposed based on the above-mentioned experimental results. Given the fact that there are a considerable amount of nanobubbles existing in protein solutions, our results indicate that nanobubbles should be considered for fully understanding the protein aggregation events in vitro.

Collision-Based Electrochemical Detection of Lysozyme Aggregation

Proteins are utilized across many biomedical and pharmaceutical industries; therefore, methods for rapid and accurate monitoring of protein aggregation are needed to ensure proper product quality. Although these processes have been previously studied, it is difficult to comprehensively evaluate protein folding and aggregation by traditional characterization techniques such as atomic force microscopy (AFM), electron microscopy, or X-ray diffraction, which require sample pre-treatment and do not represent native state proteins in solution. Herein, we report early tracking of lysozyme (Lyz) aggregation states by using single-particle collision electrochemistry (SPCE) of silver nanoparticle (AgNP) redox probes. The method relies on monitoring the rapid interaction of Lyz with AgNPs, which decreases the number of single AgNPs available for collisions and ultimately the frequency of oxidative impacts in the chronoamperometric profile. When Lyz is in a non-aggregated monomeric form, the protein forms a homogeneous coverage onto the surface of AgNPs, stabilizing the particles. When Lyz is aggregated, part of the AgNP surface remains uncoated, promoting the agglomeration of Lyz-AgNP conjugates. The frequency of AgNP impacts decreases with increasing aggregation time, providing a metric to track protein aggregation. Visualizations of integrated oxidation charge-transfer data displayed significant differences between the charge transfer per impact for AgNP samples alone and in the presence of non-aggregated and aggregated Lyz with 99% confidence using parametric ANOVA tests. Electrochemical results revealed meaningful associations with UV-vis, circular dichroism, and AFM, demonstrating that SPCE can be used as an alternative method for studying protein aggregation. This electrochemical technique could serve as a powerful tool to indirectly evaluate protein stability and screen protein samples for formation of aggregates.

Acceleration of α-synuclein fibril formation and associated cytotoxicity stimulated by silica nanoparticles as a model of neurodegenerative diseases

A wide range of biophysical and theoretical analysis were employed to explore the formation of (α-syn) amyloid fibril formation as a model of Parkinson's disease in the presence of silica oxide nanoparticles (SiO₂ NPs). Also, different cellular and molecular assays such as MTT, LDH, caspase, ROS, and qPCR were performed to reveal the α-syn amyloid fibrils-associated cytotoxicity against SH-SY5Y cells. Fluorescence measurements showed that SiO₂ NPs accelerate the α-syn aggregation and exposure of hydrophobic moieties. Congo red absorbance, circular dichroism (CD), and transmission electron microscopy (TEM) analysis depicted the SiO₂ NPs accelerated the formation of α-syn amyloid fibrils. Molecular docking study showed that SiO₂ clusters preferably bind to the N-terminal of α-syn as the helix folding site. We also realized that SiO₂ NPs increase the cytotoxicity of α-syn amyloid fibrils through a significant decrease in cell viability, increase in membrane leakage, activation of caspase-9 and -3, elevation of ROS, and increase in the ratio of Bax/Bcl2 mRNA. The cellular assay indicated that α-syn amyloid fibrils formed in the presence of SiO₂ NPs induce their cytotoxic effects through the mitochondrial-mediated intrinsic apoptosis pathway. We concluded that these data may reveal some adverse effects of NPs on the progression of Parkinson's disease.

Natural Products for the Treatment of Neurodegenerative Diseases

Neurodegenerative diseases are a heterogeneous group of disorders characterized by the progressive degeneration of the structure and function of the central nervous system or peripheral nervous system. Alzheimer's Disease (AD), Parkinson's Disease (PD) and Spinal Cord Injury (SCI) are the common neurodegenerative diseases, which typically occur in people over the age of 60. With the rapid development of an aged society, over 60 million people worldwide are suffering from these uncurable diseases. Therefore, the search for new drugs and therapeutic methods has become an increasingly important research topic. Natural products especially those from the Traditional Chinese Medicines (TCMs), are the most important sources of drugs, and have received extensive interest among pharmacist. In this review, in order to facilitate further chemical modification of those useful natural products by pharmacists, we will bring together recent studies in single natural compound from TCMs with neuroprotective effect.

Novel benzoic acid derivatives: Synthesis and biological evaluation as multitarget acetylcholinesterase and carbonic anhydrase inhibitors

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by dementia, memory impairment, cognitive dysfunction, and speech impairment. The utility of cholinergic replacement by acetylcholinesterase (AChE) inhibitors in AD treatment has been well documented so far. Recently, studies have also evidenced that human carbonic anhydrases (hCAs) serve as an important target for AD treatment. In this direction, the improvement of new multitarget drugs, which can simultaneously modulate several mechanisms or targets included in the AD pathway, may be a potent strategy to treat AD. In light of these data for understanding and developing AD-related multitarget AChE and hCAs inhibitors, in this study, novel methylene-aminobenzoic acid and tetrahydroisoquinolynyl-benzoic acid derivatives (4a-g and 6a-g) were designed. The synthesized analogs were experimentally validated for their effects by in vitro and direct enzymatic tests. Also, the compounds were subjected to in silico monitoring with Schrödinger Suite software to assign binding affinities of potential derivatives based on Glide XP scoring, molecular mechanics-generalized Born surface area computing, and validation by molecular docking. The results revealed that 6c (1,3-dimethyldihydropyrimidine-2,4-(1H,3H)-dione-substituted, K_I  value of 33.00 ± 0.29 nM), 6e (cyclohexanone-substituted, K_I  value of 18.78 ± 0.09 nM), and 6f (2,2-dimethyl-1,3-dioxan-4-one-substituted, K_I  value of 13.62 ± 0.21 nM) from the benzoic acid derivatives in this series were the most promising derivatives, as they exhibited a good multifunctional inhibition at all experimental levels and in the in silico validation against hCA I, hCA II, and AChE, respectively, for the treatment of AD.

Aggregation and Amyloidogenicity of the Nuclear Coactivator Binding Domain of CREB-Binding Protein

The nuclear coactivator binding domain (NCBD) of transcriptional co-regulator CREB-binding protein (CBP) is an example of conformationally malleable proteins that can bind to structurally unrelated protein targets and adopt distinct folds in the respective protein complexes. Here, we show that the folding landscape of NCBD contains an alternative pathway that results in protein aggregation and self-assembly into amyloid fibers. The initial steps of such protein misfolding are driven by intermolecular interactions of its N-terminal α-helix bringing multiple NCBD molecules into contact. These oligomers then undergo slow but progressive interconversion into β-sheet-containing aggregates. To reveal the concealed aggregation potential of NCBD we used a chemically synthesized mirror-image d-NCBD form. The addition of d-NCBD promoted self-assembly into amyloid precipitates presumably due to formation of thermodynamically more stable racemic β-sheet structures. The unexpected aggregation of NCBD needs to be taken into consideration given the multitude of protein-protein interactions and resulting biological functions mediated by CBP.

Multivariate Optimization of the Refolding Process of an Incorrectly Folded Fc-Fusion Protein in a Cell Culture Broth

BACKGROUND

Protein misfolding is a common problem in large-scale production of recombinant proteins, which can significantly reduce the yield of the process.

OBJECTIVE

In this work, we aimed at treating a cell culture broth containing high levels (>45%) of incorrectly folded Fc-fusion proteins by a simple redox buffer system in order to increase the proportion of the protein with correct conformation.

METHODS

Multi-variable process optimization was firstly conducted at a small scale (25 mL), employing an experimental design methodology. After identifying the key variables using a resolution IV Fractional Factorial Design (FFD), the process was then optimized by the Central Composite Design (CCD).

RESULTS

The optimal conditions for the refolding reaction were 340 mM Tris-base, 6.0 mM L-cysteine, 0.5 mM L-cystine, a buffer pH of 9.0, a reaction temperature of 8.5ºC and a reaction time of 24 h. Based on the treatment conditions obtained at a small scale, the process was further scaled up to 4500- L. The misfolded content was always less than 20%. The reaction can proceed well in the absence of chemical additives, such as chaotropic agents, aggregation suppressors, stabilizers and chelators.

CONCLUSION

The refolding process increases the fraction of active protein in the original broth reducing the burden on downstream purification steps markedly.

To be ionized or not to be ionized: the vital role of physicochemical properties of galbanic acid derivatives in AChE assay

Alzheimer's disease is a progressive neurodegenerative disorder and patients suffer from memory loss, a decline in language skill and impairment in other cognitive functions. In the cholinergic hypothesis, dysfunction of cholinergic neurons especially in the hippocampus and cerebral cortex contributes to cognitive decline in patients. So agents that enhance acetylcholine concentration could improve cognitive function. AChEIs are among the most studied anti-Alzheimer agents. Galbanic acid as a natural compound with a sesquiterpene coumarin scaffold is a weak inhibitor of AChE. In the present contribution, we discussed the impact of carboxylic group ionization on inhibitory effects. We performed in vitro and in silico studies on galbanic acid, methyl and ethyl galbanates as AChE inhibitors. The order of inhibitory effect on AChE was obtained as ethyl galbanate ∼ methyl galbanate > galbanic acid. Our study highlights the important role of the physicochemical properties of natural lead compounds in each specific assay.Communicated by Ramaswamy H. Sarma.

Structure Determination of Hen Egg-White Lysozyme Aggregates Adsorbed to Lipid/Water and Air/Water Interfaces

We use vibrational sum-frequency generation (VSFG) spectroscopy to study the structure of hen egg-white lysozyme (HEWL) aggregates adsorbed to DOPG/D₂O and air/D₂O interfaces. We find that aggregates with a parallel and antiparallel β-sheet structure together with smaller unordered aggregates and a denaturated protein are adsorbed to both interfaces. We demonstrate that to retrieve this information, fitting of the VSFG spectra is essential. The number of bands contributing to the VSFG spectrum might be misinterpreted, due to interference between peaks with opposite orientation and a nonresonant background. Our study identified hydrophobicity as the main driving force for adsorption to the air/D₂O interface. Adsorption to the DOPG/D₂O interface is also influenced by hydrophobic interaction; however, electrostatic interaction between the charged protein's groups and the lipid's headgroups has the most significant effect on the adsorption. We find that the intensity of the VSFG spectrum at the DOPG/D₂O interface is strongly enhanced by varying the pH of the solution. We show that this change is not due to a change of lysozyme's and its aggregates' charge but due to dipole reorientation at the DOPG/D₂O interface. This finding suggests that extra care must be taken when interpreting the VSFG spectrum of proteins adsorbed at the lipid/water interface.

The Effect of Limited Proteolysis by Trypsin on the Formation of Soy Protein Isolate Nanofibrils

Nanofibril system constructed by protein self-assembly is widely used in the food industry because of purposive functional properties. Soy protein isolate nanofibrils (SPINs) were reported to form via heating at pH 2.0. In this research, the soy protein isolate (SPI) hydrolysate prepared by trypsin was used as a raw material for the formation of nanofibrils called soy protein isolate hydrolysate nanofibrils (SPIHNs). Microscopic images demonstrated the formation of two nanofibrils. Based on circular dichroism spectroscopy and Thioflavin T (ThT) fluorescence spectral, we concluded that β-sheet played an important role in SPIN and SPIHN’s structural composition. At the same time, the α-helix in SPI had not been destroyed, thereby favoring the formation of SPIHN. The surface hydrophobicity of SPIHN continued to increase during the heating process and reached the highest value when heating 8 h. SDS-PAGE analysis showed that peptides produced by enzyme-modified SPI affected the formation of SPIHN. These results proposed that enzymatic hydrolysis prior to acidic during fibrillation process affected the fibrillation of SPI, and the peptides formed by enzymatic hydrolysis were more efficient for the self-assembly process. This study will provide a theoretical basis for the future research of SPI nanofibril functionality.

Model for Counterion Binding and Charge Reversal on Protein Surfaces

The structural stability and solubility of proteins in liquid therapeutic formulations is important, especially since new generations of therapeutics are designed for efficacy before consideration of stability. We introduce an electrostatic binding model to measure the net charge of proteins with bound ions in solution. The electrostatic potential on a protein surface is used to separately group together acidic and basic amino acids into patches, which are then iteratively bound with oppositely charged counterions. This model is aimed toward formulation chemists for initial screening of a range of conditions prior to lab-work. Computed results compare well with experimental zeta potential measurements from the literature covering a range of solution conditions. Importantly, the binding model reproduces the charge reversal phenomenon that is observed with polyvalent ion binding to proteins and its dependence on ion charge and concentration. Intriguingly, protein sequence can be used to give similarly good agreement with experiment as protein structure, interpreted as resulting from the close proximity of charged side chains on a protein surface. Further, application of the model to human proteins suggests that polyanion binding and overcharging, including charge reversal for cationic proteins, is a general feature. These results add to evidence that addition of polyanions to protein formulations could be a general mechanism for modulating solution stability.

Order, Disorder, and Reorder State of Lysozyme: Aggregation Mechanism by Raman Spectroscopy

Lysozyme, like many other well-folded globular proteins, under stressful conditions produces nanoscale oligomer assembly and amyloid-like fibrillar aggregates. With engaging Raman microscopy, we made a critical structural analysis of oligomer and other assembly structures of lysozyme obtained from hen egg white and provided a quantitative estimation of a protein secondary structure in different states of its fibrillation. A strong amide I Raman band at 1660 cm^-1 and a N-Cα-C stretching band at ∼930 cm^-1 clearly indicated the presence of a substantial amount of α-helical folds of the protein in its oligomeric assembly state. In addition, analysis of the amide III region and Raman difference spectra suggested an ample presence of a PPII-like secondary structure in these oligomers without causing major loss of α-helical folds, which is found in the case of monomeric samples. Circular dichroism study also revealed the presence of typical α-helical folds in the oligomeric state. Nonetheless, most of the Raman bands associated with aromatic residues and disulfide (-S-S-) linkages broadened in the oligomeric state and indicated a collapse in the tertiary structure. In the fibrillar state of assembly, the amide I band became much sharper and enriched with the β-sheet secondary structure. Also, the disulfide bond vibration in matured fibrils became much weaker compared to monomer and oligomers and thus confirmed certain loss/cleavage of this bond during fibrillation. The Raman band of tryptophan and tyrosine residues indicated that some of these residues experienced a greater hydrophobic microenvironment in the fibrillar state than the protein in the oligomeric state of the assembly structure.

Biophysical Elucidation of Amyloid Fibrillation Inhibition and Prevention of Secondary Nucleation by Cholic Acid: An Unexplored Function of Cholic Acid

Protein misfolding and its deviant self-assembly to converge into amyloid fibrils is associated with the perturbation of cellular functions and thus with debilitating neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, etc. A great deal of research has already been carried out to discover a potential amyloid inhibitor that can slow down, prevent, or remodel toxic amyloids. In the present study with the help of a combination of biophysical, imaging, and computational techniques, we investigated the mechanism of interaction of cholic acid (CA), a primary bile acid, with human insulin and Aβ-42 and found CA to be effective in inhibiting amyloid formation. From ThT data, we inferred that CA encumbers amyloid fibrillation up to 90% chiefly by targeting elongation of fibrils with an insignificant effect on lag time, while in the case of Aβ-42, CA stabilizes the peptide in its native state preventing its fibrillation. Strikingly upon adding initially at the secondary nucleation stage, CA also detained the progression/growth of insulin fibrils. CA is unable to prevent the conformational changes completely during fibrillation but tends to resist and maintain an α helical structure up to a significant extent at a primary nucleation stage while reducing the β sheet rich content at the secondary nucleation stage. Moreover, CA treated samples exhibited reduced cytotoxicity and different morphology. Furthermore, the results obtained after molecular docking indicated that CA is interacting with insulin via hydrogen bonds. For future research, this study can be considered as preliminary research for the development of CA, a metabolite of our body, as a potential therapeutic agent against Alzheimer's disease without even stimulating the immunological responses.

Preparation and in vitro evaluation of multi-target-directed selenium-chondroitin sulfate nanoparticles in protecting against the Alzheimer's disease

The purpose of this study was to ascertain the effect of selenium-chondroitin sulfate nanoparticles (CS@Se) on multi-target-directed therapy for the treatment of Alzheimer's disease (AD). CS@Se nanoparticles were successfully synthesized, and their therapeutic effects were studied in in vitro AD models. CS@Se effectively inhibited amyloid-β (Aβ) aggregation and protected SH-SY5Y cells from Aβ_1-42-induced cytotoxicity. Moreover, CS@Se significantly decreased okadaic acid-induced actin cytoskeleton instability in SH-SY5Y cells. In addition, CS@Se decreased the levels of reactive oxygen species (ROS) and malondialdehyde (MDA) and increased the levels of glutathione peroxidase (GSH-Px). The Western blot results indicated that CS@Se attenuated the hyperphosphorylation of tau (Ser396/Ser404) by regulating the expression of GSK-3β. In summary, this study demonstrated that CS@Se could inhibit the aggregation of Aβ, reduce damage to the cytoskeleton, mitigate oxidative stress and attenuate the hyperphosphorylation of tau protein. CS@Se might be a potent multi-functional agent for the treatment of AD and thus warrants further research and evaluation.

Inhibition of Amyloid Fibrillation by Small Molecules and Nanomaterials: Strategic Development of Pharmaceuticals Against Amyloidosis

Amyloid fibrils are a special class of self-assembled protein molecules, which exhibit various toxic effects in cells. Different physiological disorders such as Alzheimer's, Parkinson's, Huntington's diseases, etc. happen due to amyloid formation and lack of proper cellular mechanism for the removal of fibrils. Therefore, inhibition of amyloid fibrillation will find immense applications to combat the diseases associated with amyloidosis. The development of therapeutics against amyloidosis is definitely challenging and numerous strategies have been followed to find out anti-amyloidogenic molecules. Inhibition of amyloid aggregation of proteins can be achieved either by stabilizing the native conformation or by decreasing the chances of assembly formation by the unfolded/misfolded structures. Various small molecules such as naturally occurring polyphenols, flavonoids, small organic molecules, surfactants, dyes, chaperones, etc. have demonstrated their capability to interrupt the amyloid fibrillation of proteins. In addition to that, in last few years, different nanomaterials were evolved as effective therapeutic inhibitors against amyloidosis. Aromatic and hydrophobic interactions between the partially unfolded protein molecules and the inhibitors had been pointed as a general mechanism for inhibition. In this review article, we are presenting an overview on the inhibition of amyloidosis by using different small molecules (both natural and synthetic origin) as well as nanomaterials for development of pharmaceutical strategies against amyloid diseases.