αB-Crystallin inhibits the cell toxicity associated with amyloid fibril formation by κ-casein and the amyloid-β peptide

Classification of amyloidosis and protein misfolding disorders in animals 2024: A review on pathology and diagnosis

Amyloidosis is a group of diseases in which proteins become amyloid, an insoluble fibrillar aggregate, resulting in organ dysfunction. Amyloid deposition has been reported in various animal species. To diagnose and understand the pathogenesis of amyloidosis, it is important to identify the amyloid precursor protein involved in each disease. Although 42 amyloid precursor proteins have been reported in humans, little is known about amyloidosis in animals, except for a few well-described amyloid proteins, including amyloid A (AA), amyloid light chain (AL), amyloid β (Aβ), and islet amyloid polypeptide-derived amyloid. Recently, several types of novel amyloidosis have been identified in animals using immunohistochemistry and mass spectrometry-based proteomic analysis. Certain species are predisposed to specific types of amyloidosis, suggesting a genetic background for its pathogenesis. Age-related amyloidosis has also emerged due to the increased longevity of captive animals. In addition, experimental studies have shown that some amyloids may be transmissible. Accurate diagnosis and understanding of animal amyloidosis are necessary for appropriate therapeutic intervention and comparative pathological studies. This review provides an updated classification of animal amyloidosis, including associated protein misfolding disorders of the central nervous system, and the current understanding of their pathogenesis. Pathologic features are presented together with state-of-the-art diagnostic methods that can be applied for routine diagnosis and identification of novel amyloid proteins in animals.

Modulation of Alzheimer's Disease Aβ40 Fibril Polymorphism by the Small Heat Shock Protein αB-Crystallin

Deposition of amyloid plaques in the brains of Alzheimer's disease (AD) patients is a hallmark of the disease. AD plaques consist primarily of the beta-amyloid (Aβ) peptide but can contain other factors such as lipids, proteoglycans, and chaperones. So far, it is unclear how the cellular environment modulates fibril polymorphism and how differences in fibril structure affect cell viability. The small heat-shock protein (sHSP) alpha-B-Crystallin (αBC) is abundant in brains of AD patients, and colocalizes with Aβ amyloid plaques. Using solid-state NMR spectroscopy, we show that the Aβ40 fibril seed structure is not replicated in the presence of the sHSP. αBC prevents the generation of a compact fibril structure and leads to the formation of a new polymorph with a dynamic N-terminus. We find that the N-terminal fuzzy coat and the stability of the C-terminal residues in the Aβ40 fibril core affect the chemical and thermodynamic stability of the fibrils and influence their seeding capacity. We believe that our results yield a better understanding of how sHSP, such as αBC, that are part of the cellular environment, can affect fibril structures related to cell degeneration in amyloid diseases.

Biological effects and mechanism of β-amyloid aggregation inhibition by penetrable recombinant human HspB5-ACD structural domain protein

Alzheimer's disease (AD) is a global medical challenge. Studies have shown that neurotoxicity caused by pathological aggregation of β-amyloid (Aβ) is an important factor leading to AD. Therefore, inhibiting the pathological aggregation of Aβ is the key to treating AD. The recombinant human HspB5-ACD structural domain protein (AHspB5) prepared by our group in the previous period has been shown to have anti-amyloid aggregation effects, but its inability to penetrate biological membranes has limited its development. In this study, we prepared a recombinant fusion protein (T-AHspB5) of TAT and AHspB5. In vitro experiments showed that T-AHspB5 inhibited the formation of Aβ1-42 protofibrils and had the ability to penetrate the blood-brain barrier; in cellular experiments, T-AHspB5 prevented Aβ1-42-induced oxidative stress damage, apoptosis, and inflammatory responses in neuronal cells, and its mechanism of action was related to microglia activation and mitochondria-dependent apoptotic pathway. In animal experiments, T-AHspB5 improved memory and cognitive dysfunction and inhibited pathological changes of AD in APP/PS1 mice. In conclusion, this paper is expected to reveal the intervention mechanism and biological effect of T-AHspB5 on pathological aggregation of Aβ1-42, provide a new pathway for the treatment of AD, and lay the foundation for the future development and application of T-AHspB5.

Molecular Insights into the Inhibitory Role of α-Crystallin against γD-Crystallin Aggregation

Cataracts, a major cause of global blindness, contribute significantly to the overall prevalence of blindness. The opacification of the lens, resulting in cataract formation, primarily occurs due to the aggregation of crystallin proteins within the eye lens. Despite the high concentration of these crystallins, they remarkably maintain the lens transparency and refractive index. α-Crystallins (α-crys), acting as chaperones, play a crucial role in preventing crystallin aggregation, although the exact molecular mechanism remains uncertain. In this study, we employed a combination of molecular docking, all-atom molecular dynamics simulations, and advanced free energy calculations to investigate the interaction between γD-crystallin (γD-crys), a major structural protein of the eye lens, and α-crystallin proteins. Our findings demonstrate that α-crys exhibits an enhanced affinity for the NTD2 and CTD4 regions of γD-crys. The NTD2 and CTD4 regions form the interface between the N-terminal domain (NTD) and the C-terminal domain (CTD) of the γD-crys protein. By binding to the interface region between the NTD and CTD of the protein, α-crys effectively inhibits the formation of domain-swapped aggregates and mitigates protein aggregation. Analysis of the Markov state models using molecular dynamics trajectories confirms that minimum free energy conformations correspond to the binding of the α-crystallin domain (ACD) of α-crys to NTD2 and CTD4 that form the interdomain interface.

Identification of novel amyloidosis in dogs: α-S1-casein acquires amyloidogenicity in mammary tumor by overexpression and N-terminal truncation

Mammary tumor-associated amyloidosis (MTAA) in dogs is characterized by amyloid deposition in the stroma of mammary adenoma or carcinoma; however, the amyloid precursor protein remains unknown. We attempted to identify an amyloid precursor protein and elucidated its etiology by characterizing 5 cases of canine MTAA. Proteomic analyses of amyloid extracts from formalin-fixed paraffin-embedded specimens revealed α-S1-casein (CASA1) as a prime candidate and showed the N-terminal truncation of canine CASA1. Both immunohistochemistry and immunoelectron microscopy showed that amyloid deposits or fibrils in MTAA cases were positive for CASA1. Reverse transcription-polymerase chain reaction and quantitative polymerase chain reaction revealed the complete mRNA sequence encoding CASA1, whose expression was significantly higher in the amyloid-positive group. The recombinant protein of the N-terminal-truncated canine CASA1 and the synthetic peptides derived from canine and human CASA1 formed amyloid-like fibrils in vitro. Structural prediction suggested that the N-terminal region of CASA1 was disordered. Previously, full-length CASA1 was reported to inhibit the amyloidogenesis of other proteins; however, we demonstrated that CASA1 acquires amyloidogenicity via excessive synthesis followed by truncation of its disordered N-terminal region. By identifying a novel in vivo amyloidogenic protein in animals and revealing key mechanistic details of its associated pathology, this study provides valuable insights into the integrated understanding of related proteopathies.

Dissecting the Inhibitory Mechanism of the αB-Crystallin Domain against Aβ42 Aggregation and Its Effect on Aβ42 Protofibrils: A Molecular Dynamics Simulation Study

Alzheimer's disease (AD) is related to the misfolding and aggregation of amyloid-β (Aβ) protein, and its major pathological hallmark is fibrillary β-amyloid plaques. Impeding the formation of Aβ β-structure-rich aggregates and dissociating Aβ fibrils are considered potent strategies to suppress the onset and progression of AD. As a molecular chaperone, human αB-crystallin has received extensive attention in the inhibition of protein aggregation. Previous experiments reported that the structured core region of αB-crystallin (αBC) exhibits a better preventive effect on Aβ aggregation and toxicity than the full-length protein. However, the molecular mechanism behind the effect of inhibition remains mostly unknown. Herein, we carried out six 500 ns molecular dynamics (MD) simulations to investigate the inhibitory mechanism of αBC on Aβ₄₂ aggregation. Our simulations show that αBC greatly impedes the formation of β-structure contents. We find that the binding of αBC to the Aβ₄₂ monomer is driven by polar, hydrophobic, and H-bonding interactions. To explore whether αBC could destabilize Aβ₄₂ protofibrils, we also carried out MD simulations of Aβ₄₂ protofibrils with and without αBC. The results show that αBC interacts with three binding sites of the Aβ₄₂ protofibril, and the binding is mainly driven by polar and H-bonding interactions. The binding of αBC at these three sites has a preferred dissociation effect on the β-structure content, kink angle, and K28-A42 salt bridges. Overall, this study not only discloses the molecular mechanism of αBC against Aβ₄₂ aggregation but also demonstrates the disruption effects of αBC on Aβ₄₂ protofibrils, which yields an avenue for designing anti-AD drug candidates.

Alzheimer's disease amyloid-β pathology in the lens of the eye

Neuropathological hallmarks of Alzheimer's disease (AD) include pathogenic accumulation of amyloid-β (Aβ) peptides and age-dependent formation of amyloid plaques in the brain. AD-associated Aβ neuropathology begins decades before onset of cognitive symptoms and slowly progresses over the course of the disease. We previously reported discovery of Aβ deposition, β-amyloidopathy, and co-localizing supranuclear cataracts (SNC) in lenses from people with AD, but not other neurodegenerative disorders or normal aging. We confirmed AD-associated Aβ molecular pathology in the lens by immunohistopathology, amyloid histochemistry, immunoblot analysis, epitope mapping, immunogold electron microscopy, quantitative immunoassays, and tryptic digest mass spectrometry peptide sequencing. Ultrastructural analysis revealed that AD-associated Aβ deposits in AD lenses localize as electron-dense microaggregates in the cytoplasm of supranuclear (deep cortex) fiber cells. These Aβ microaggregates also contain αB-crystallin and scatter light, thus linking Aβ pathology and SNC phenotype expression in the lenses of people with AD. Subsequent research identified Aβ lens pathology as the molecular origin of the distinctive cataracts associated with Down syndrome (DS, trisomy 21), a chromosomal disorder invariantly associated with early-onset Aβ accumulation and Aβ amyloidopathy in the brain. Investigation of 1249 participants in the Framingham Eye Study found that AD-associated quantitative traits in brain and lens are co-heritable. Moreover, AD-associated lens traits preceded MRI brain traits and cognitive deficits by a decade or more and predicted future AD. A genome-wide association study of bivariate outcomes in the same subjects identified a new AD risk factor locus in the CTNND2 gene encoding δ-catenin, a protein that modulates Aβ production in brain and lens. Here we report identification of AD-related human Aβ (hAβ) lens pathology and age-dependent SNC phenotype expression in the Tg2576 transgenic mouse model of AD. Tg2576 mice express Swedish mutant human amyloid precursor protein (APP-Swe), accumulate hAβ peptides and amyloid pathology in the brain, and exhibit cognitive deficits that slowly progress with increasing age. We found that Tg2576 trangenic (Tg⁺) mice, but not non-transgenic (Tg^-) control mice, also express human APP, accumulate hAβ peptides, and develop hAβ molecular and ultrastructural pathologies in the lens. Tg2576 Tg⁺ mice exhibit age-dependent Aβ supranuclear lens opacification that recapitulates lens pathology and SNC phenotype expression in human AD. In addition, we detected hAβ in conditioned medium from lens explant cultures prepared from Tg⁺ mice, but not Tg^- control mice, a finding consistent with constitutive hAβ generation in the lens. In vitro studies showed that hAβ promoted mouse lens protein aggregation detected by quasi-elastic light scattering (QLS) spectroscopy. These results support mechanistic (genotype-phenotype) linkage between Aβ pathology and AD-related phenotypes in lens and brain. Collectively, our findings identify Aβ pathology as the shared molecular etiology of two age-dependent AD-related cataracts associated with two human diseases (AD, DS) and homologous murine cataracts in the Tg2576 transgenic mouse model of AD. These results represent the first evidence of AD-related Aβ pathology outside the brain and point to lens Aβ as an optically-accessible AD biomarker for early detection and longitudinal monitoring of this devastating neurodegenerative disease.

Are casein micelles extracellular condensates formed by liquid-liquid phase separation?

Casein micelles are extracellular polydisperse assemblies of unstructured casein proteins. Caseins are the major component of milk. Within casein micelles, casein molecules are stabilised by binding to calcium phosphate nanoclusters and, by acting as molecular chaperones, through multivalent interactions. In light of such interactions, we discuss whether casein micelles can be considered as extracellular condensates formed by liquid-liquid phase separation. We analyse the sequence, structure and interactions of caseins in comparison to proteins forming intracellular condensates. Furthermore, we review the similarities between caseins and small heat-shock proteins whose chaperone activity is linked to phase separation of proteins. By bringing these observations together, we describe a regulatory mechanism for protein condensates, as exemplified by casein micelles.

The Monomeric α-Crystallin Domain of the Small Heat-shock Proteins αB-crystallin and Hsp27 Binds Amyloid Fibril Ends

Small heat-shock proteins (sHSPs) are ubiquitously expressed molecular chaperones present in all kingdoms of life that inhibit protein misfolding and aggregation. Despite their importance in proteostasis, the structure-function relationships of sHSPs remain elusive. Human sHSPs are characterised by a central, highly conserved α-crystallin domain (ACD) and variable-length N- and C-terminal regions. The ACD forms antiparallel homodimers via an extended β-strand, creating a shared β-sheet at the dimer interface. The N- and C-terminal regions mediate formation of higher order oligomers that are thought to act as storage forms for chaperone-active dimers. We investigated the interactions of the ACD of two human sHSPs, αB-crystallin (αB-C) and Hsp27, with apolipoprotein C-II amyloid fibrils using analytical ultracentrifugation and nuclear magnetic resonance spectroscopy. The ACD was found to interact transiently with amyloid fibrils to inhibit fibril elongation and naturally occurring fibril end-to-end joining. This interaction was sensitive to the concentration of fibril ends indicating a 'fibril-capping' interaction. Furthermore, resonances arising from the ACD monomer were attenuated to a greater extent than those of the ACD dimer in the presence of fibrils, suggesting that the monomer may bind fibrils. This hypothesis was supported by mutagenesis studies in which disulfide cross-linked ACD dimers formed by both αB-C and Hsp27 were less effective at inhibiting amyloid fibril elongation and fibril end-to-end joining than ACD constructs lacking disulfide cross-linking. Our results indicate that sHSP monomers inhibit amyloid fibril elongation, highlighting the importance of the dynamic oligomeric nature of sHSPs for client binding.

Influence of Chaperones on Amyloid Formation of Аβ Peptide

Background:

An extensive study of the folding and stability of proteins and their complexes has revealed a number of problems and questions that need to be answered. One of them is the effect of chaperones on the process of fibrillation of various proteins and peptides.

Methods:

We studied the effect of molecular chaperones, such as GroEL and α-crystallin, on the fibrillogenesis of the Aβ(1-42) peptide using electron microscopy and surface plasmon resonance.

Results:

Recombinant GroEL and Aβ(1-42) were isolated and purified. It was shown that the assembly of GroEL occurs without the addition of magnesium and potassium ions, as is commonly believed. According to the electron microscopy results, GroEL insignificantly affects the fibrillogenesis of the Aβ(1-42) peptide, while α-crystallin prevents the elongation of the Aβ(1-42) peptide fibrils. We have demonstrated that GroEL interacts nonspecifically with Aβ(1-42), while α-crystallin does not interact with Aβ(1-42) at all using surface plasmon resonance.

Conclusion:

The data obtained will help us understand the process of amyloid formation and the effect of various components on it.

Plant protein-based fibers: Fabrication, characterization, and potential food applications

Proteins from plants have been considered as safer, healthier, and more sustainable resources than their animal counterparts. However, incomplete amino acid composition and relatively poor functionality limit their applications in foods. Structuring plant proteins to fibrous architectures enhances their physicochemical properties, which can favor various food applications. This review primarily focuses on fabrication of fibers from plant proteins via self-assembly, electrospinning, solution blow spinning, wet spinning, and high-temperature shear, as well as on several applications where such fibrous proteins assemble in quality foods. The changes of protein structure and protein-protein interactions during fiber production are discussed in detail, along with the effects of fabrication conditions and protein sources on the morphology and function of the fibers. Self-assembly requires proteolysis and subsequent peptide aggregation under specific conditions, which can be influenced by pH, salt and protein type. The spinning strategy is more scalable and produces uniformed fibers with larger length scales suitable for encapsulation, food packaging and sensor substrates. Significant progress has been made on high-temperature shear (including extrusion)-induced fibers responsible for desirable texture in meat analogues. Structuring plant proteins adds values for broadened food applications, but it remains challenging to keep processes cost-effective and environmentally friendly using food grade solvents.

αB-Crystallin Chaperone Inhibits Aβ Aggregation by Capping the β-Sheet-Rich Oligomers and Fibrils

Inhibiting the cytotoxicity of amyloid aggregation by endogenous proteins is a promising strategy against degenerative amyloid diseases due to their intrinsically high biocompatibility and low immunogenicity. In this study, we investigated the inhibition mechanism of the structured core region of αB-crystallin (αBC) against Aβ fibrillization using discrete molecular dynamics simulations. Our computational results recapitulated the experimentally observed Aβ binding sites in αBC and suggested that αBC could bind to various Aβ aggregate species during the aggregation process-including monomers, dimers, and likely other high molecular weight oligomers, protofibrils, and fibrils-by capping the exposed β-sheet elongation surfaces. Thus, the nucleation of Aβ oligomers into fibrils and the fibril growth could be inhibited. Mechanistic insights obtained from our systematic computational studies may aid in the development of novel therapeutic strategies to modulate the aggregation of pathological, amyloidogenic protein in degenerative diseases.

Development of a brain-permeable peptide nanofiber that prevents aggregation of Alzheimer pathogenic proteins

Alzheimer's disease (AD) is proposed to be induced by abnormal aggregation of amyloidβ in the brain. Here, we designed a brain-permeable peptide nanofiber drug from a fragment of heat shock protein to suppress aggregation of the pathogenic proteins. To facilitate delivery of the nanofiber into the brain, a protein transduction domain from Drosophila Antennapedia was incorporated into the peptide sequence. The resulting nanofiber efficiently suppressed the cytotoxicity of amyloid βby trapping amyloid β onto its hydrophobic nanofiber surface. Moreover, the intravenously or intranasally injected nanofiber was delivered into the mouse brain, and improved the cognitive function of an Alzheimer transgenic mouse model. These results demonstrate the potential therapeutic utility of nanofibers for the treatment of AD.

The multifaceted nature of αB-crystallin

In vivo, small heat-shock proteins (sHsps) are key players in maintaining a healthy proteome. αB-crystallin (αB-c) or HspB5 is one of the most widespread and populous of the ten human sHsps. Intracellularly, αB-c acts via its molecular chaperone action as the first line of defence in preventing target protein unfolding and aggregation under conditions of cellular stress. In this review, we explore how the structure of αB-c confers its function and interactions within its oligomeric self, with other sHsps, and with aggregation-prone target proteins. Firstly, the interaction between the two highly conserved regions of αB-c, the central α-crystallin domain and the C-terminal IXI motif and how this regulates αB-c chaperone activity are explored. Secondly, subunit exchange is rationalised as an integral structural and functional feature of αB-c. Thirdly, it is argued that monomeric αB-c may be its most chaperone-species active, but at the cost of increased hydrophobicity and instability. Fourthly, the reasons why hetero-oligomerisation of αB-c with other sHsps is important in regulating cellular proteostasis are examined. Finally, the interaction of αB-c with aggregation-prone, partially folded target proteins is discussed. Overall, this paper highlights the remarkably diverse capabilities of αB-c as a caretaker of the cell.

Small heat shock proteins in neurodegenerative diseases

Small heat shock proteins are ubiquitously expressed chaperones, yet mutations in some of them cause tissue-specific diseases. Here, we will discuss how small heat shock proteins give rise to neurodegenerative disorders themselves while we will also highlight how these proteins can fulfil protective functions in neurodegenerative disorders caused by protein aggregation. The first half of this paper will be focused on how mutations in HSPB1, HSPB3, and HSPB8 are linked to inherited peripheral neuropathies like Charcot-Marie-Tooth (CMT) disease and distal hereditary motor neuropathy (dHMN). The second part of the paper will discuss how small heat shock proteins are linked to neurodegenerative disorders like Alzheimer's, Parkinson's, and Huntington's disease.

Small Heat Shock Proteins, Big Impact on Protein Aggregation in Neurodegenerative Disease

Misfolding, aggregation, and aberrant accumulation of proteins are central components in the progression of neurodegenerative disease. Cellular molecular chaperone systems modulate proteostasis, and, therefore, are primed to influence aberrant protein-induced neurotoxicity and disease progression. Molecular chaperones have a wide range of functions from facilitating proper nascent folding and refolding to degradation or sequestration of misfolded substrates. In disease states, molecular chaperones can display protective or aberrant effects, including the promotion and stabilization of toxic protein aggregates. This seems to be dependent on the aggregating protein and discrete chaperone interaction. Small heat shock proteins (sHsps) are a class of molecular chaperones that typically associate early with misfolded proteins. These interactions hold proteins in a reversible state that helps facilitate refolding or degradation by other chaperones and co-factors. These sHsp interactions require dynamic oligomerization state changes in response to diverse cellular triggers and, unlike later steps in the chaperone cascade of events, are ATP-independent. Here, we review evidence for modulation of neurodegenerative disease-relevant protein aggregation by sHsps. This includes data supporting direct physical interactions and potential roles of sHsps in the stewardship of pathological protein aggregates in brain. A greater understanding of the mechanisms of sHsp chaperone activity may help in the development of novel therapeutic strategies to modulate the aggregation of pathological, amyloidogenic proteins. sHsps-targeting strategies including modulators of expression or post-translational modification of endogenous sHsps, small molecules targeted to sHsp domains, and delivery of engineered molecular chaperones, are also discussed.

Food protein amyloid fibrils: Origin, structure, formation, characterization, applications and health implications

Amyloid fibrils have traditionally been considered only as pathological aggregates in human neurodegenerative diseases, but it is increasingly becoming clear that the propensity to form amyloid fibrils is a generic property for all proteins, including food proteins. Differently from the pathological amyloid fibrils, those derived from food proteins can be used as advanced materials in biomedicine, tissue engineering, environmental science, nanotechnology, material science as well as in food science, owing to a combination of highly desirable feature such as extreme aspect ratios, outstanding stiffness and a broad availability of functional groups on their surfaces. In food science, protein fibrillization is progressively recognized as an appealing strategy to broaden and improve food protein functionality. This review article discusses the various classes of reported food protein amyloid fibrils and their formation conditions. It furthermore considers amyloid fibrils in a broad context, from their structural characterization to their forming mechanisms and ensued physical properties, emphasizing their applications in food-related fields. Finally, the biological fate and the potential toxicity mechanisms of food amyloid fibrils are discussed, and an experimental protocol for their health safety validation is proposed in the concluding part of the review.

Protein nanotubes as state-of-the-art nanocarriers: Synthesis methods, simulation and applications

Application of food proteins as a tool to form nanostructures (especially nanotubular shapes) has been an interesting topic for both the food and pharmaceutical sectors. Organic and protein nanostructures have better biocompatibility and biodegradability compared to inorganic counterparts like carbon nanotubes; in addition, they can undergo surface modifications. Several organic nanotubes have been developed, meanwhile, the engineered protein nanotubes in the food science have been prepared from α-lactalbumin, ovalbumin, cyclic peptide nanotubes, collagen, bovine serum albumin, lysozyme and hydrophobins which are of great interest to be applied in the food industry considering their outstanding properties. This revision underlines the production of protein nanotubular structures and their applications as well as introducing the in silico studies which is a novel field in predicting the interactions of proteins with different molecules before running experimental tests and finally exploring the safety of protein nanotubes. Protein nanotubes have several advantages over other morphologies, such as the functionalizing ability of both the outer and inner layers, enabling an efficient delivery and controlled release and their ability as gelling agents. Also, regarding their natural source in foods, they are promising alternatives to carbon nanotubes.

Chaperoning Against Amyloid Aggregation: Monitoring In Vitro and In Vivo

Protein aggregation and inclusion body formation have been a key causal phenomenon behind a majority of neurodegenerative disorders. Various approaches aimed at preventing the formation/elimination of protein aggregates are being developed to control these diseases. Molecular chaperones are a class of protein that not only direct the functionally relevant fold of the protein but also perform quality control against stress, misfolding/aggregation. Genes that encode molecular chaperones are induced and expressed in response to extreme stress conditions to "salvage" the cell by the "unfolded protein response" (UPR) signaling pathway. Here we describe in detail the various in vitro and in vivo assays involved in identifying the chaperone activity of proteins using human calnuc as a model protein. Calnuc is a Golgi resident, calcium-binding protein, identified as chaperone protein and is reported to protect the cells against the cytotoxicity caused by amyloidosis and ER stress. Calnuc is also reported to regulate G_αi activity and inflammation apart from the role of chaperoning against amyloid proteins.

Studies of the Process of Amyloid Formation by Aβ Peptide

Studies of the process of amyloid formation by Aβ peptide have been topical due to the critical role of this peptide in the pathogenesis of Alzheimer's disease. Many articles devoted to this process are available in the literature; however, none of them gives a detailed description of the mechanism of the process of generation of amyloids. Moreover, there are no reliable data on the influence of modified forms of Aβ peptide on its amyloid formation. To appreciate the role of Aβ aggregation in the pathogenesis of Alzheimer's disease and to develop a strategy for its treatment, it is necessary to have a well-defined description of the molecular mechanism underlying the formation of amyloids as well as the contribution of each intermediate to this process. We are convinced that a combined analysis of theoretical and experimental methods is a way for understanding molecular mechanisms of numerous diseases. Based on our experimental data and molecular modeling, we have constructed a general model of the process of amyloid formation by Aβ peptide. Using the data described in our previous publications, we propose a model of amyloid formation by this peptide that differs from the generally accepted model. Our model can be applied to other proteins and peptides as well. According to this model, the main building unit for the formation of amyloid fibrils is a ring-like oligomer. Upon interaction with each other, ring-like oligomers form long fibrils of different morphology. This mechanism of generation of amyloid fibrils may be common for other proteins and peptides.

Chaperone-like Activity of Calnuc Prevents Amyloid Aggregation

Calnuc is a ubiquitously expressed protein of the EF-hand Ca²⁺-binding superfamily. Previous studies have implicated it in Ca²⁺-sensitive physiological processes, whereas details of its function and involvement in human diseases are lacking. Drawing upon the sequence homology of calnuc with calreticulin, we propose it functions as a molecular chaperone-like protein. In cells under thermal, chemical [urea and guanidinium chloride (GdmCl)], and acidic stress, calnuc exhibits properties similar to those of established chaperone-like proteins (GRP78, spectrin, and α-crystallin), effectively demonstrated by its ability to suppress aggregation of malate dehydrogenase (MDH), alcohol dehydrogenase, and catalase. Calnuc aids in refolding of MDH with retention of 80% of its enzymatic activity. In HEK293 cells subjected to heat shock, calnuc chaperones luciferase, protecting its activity. Our in vitro and cell culture results establish the ability of calnuc to inhibit fibrillation of insulin and lysozyme and validate its neuroprotective role in cells treated with amyloid fibrils. Calnuc also rescues cells from fibrillar toxicity (caused by misfolded or aggregated proteins), providing a plausible explanation for the previous observation of its low level of expression in brains affected by Alzheimer's disease. We propose that calnuc is possibly involved in controlling protein unfolding diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), prion disease, and type II diabetes.

The Effect of Milk Constituents and Crowding Agents on Amyloid Fibril Formation by κ-Casein

When not incorporated into the casein micelle, κ-casein, a major milk protein, rapidly forms amyloid fibrils at physiological pH and temperature. In this study, the effects of milk components (calcium, lactose, lipids, and heparan sulfate) and crowding agents on reduced and carboxymethylated (RCM) κ-casein fibril formation was investigated using far-UV circular dichroism spectroscopy, thioflavin T binding assays, and transmission electron microscopy. Longer-chain phosphatidylcholine lipids, which form the lining of milk ducts and milk fat globules, enhanced RCM κ-casein fibril formation irrespective of whether the lipids were in a monomeric or micellar state, whereas shorter-chain phospholipids and triglycerides had little effect. Heparan sulfate, a component of the milk fat globule membrane and catalyst of amyloid deposition in extracellular tissue, had little effect on the kinetics of RCM κ-casein fibril formation. Major nutritional components such as calcium and lactose also had no significant effect. Macromolecular crowding enhances protein-protein interactions, but in contrast to other fibril-forming species, the extent of RCM κ-casein fibril formation was reduced by the presence of a variety of crowding agents. These data are consistent with a mechanism of κ-casein fibril formation in which the rate-determining step is dissociation from the oligomer to give the highly amyloidogenic monomer. We conclude that the interaction of κ-casein with membrane-associated phospholipids along its secretory pathway may contribute to the development of amyloid deposits in mammary tissue. However, the formation of spherical oligomers such as casein micelles is favored over amyloid fibrils in the crowded environment of milk, within which the occurrence of amyloid fibrils is low.

Evaluation of protease resistance and toxicity of amyloid-like food fibrils from whey, soy, kidney bean, and egg white

The structural properties of amyloid fibrils combined with their highly functional surface chemistry make them an attractive new food ingredient, for example as highly effective gelling agents. However, the toxic role of amyloid fibrils in disease may cause some concern about their food safety because it has not been established unequivocally if consumption of food fibrils poses a health risk to consumers. Here we present a study of amyloid-like fibrils from whey, kidney bean, soy bean, and egg white to partially address this concern. Fibrils showed varied resistance to proteolytic digestion in vitro by either Proteinase K, pepsin or pancreatin. The toxicity of mature fibrils was measured in vitro and compared to native protein, early-stage-fibrillar protein, and sonicated fibrils in two immortalised human cancer cell lines, Caco-2 and Hec-1a. There was no reduction in the viability of either Caco-2 or Hec-1a cells after treatment with a fibril concentration of up to 0.25 mg/mL.

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

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

The mitochondria-targeted antioxidant SkQ1 restores αB-crystallin expression and protects against AMD-like retinopathy in OXYS rats

Age-related macular degeneration (AMD), a neurodegenerative and vascular retinal disease, is the leading cause of blindness in the developed world. Accumulating evidence suggests that alterations in the expression of a small heat shock protein (αB-crystallin) are involved in the pathogeneses of AMD. Here we demonstrate that senescence-accelerated OXYS rats-an animal model of the dry form of AMD-develop spontaneous retinopathy against the background of reduced expression of αB-crystallin in the retina at the early preclinical stages of retinopathy (age 20 days) as well as at 4 and 24 months of age, during the progressive stage of the disease. The level of αA-crystallin expression in the retina of OXYS rats at all the ages examined was no different from that in disease-free Wistar rats. Treatment with the mitochondria-targeted antioxidant SkQ1 (plastoquinonyl-decyltriphenylphosphonium) from 1.5 to 4 months of age, 250 nmol/kg, increased the level of αB-crystallin expression in the retina of OXYS rats. SkQ1 slowed the development of retinopathy and reduced histological aberrations in retinal pigment epithelium cells. SkQ1 also attenuated neurodegenerative changes in the photoreceptors and facilitated circulation in choroid blood vessels in the retina of OXYS rats; this improvement was probably linked with the restoration of αB-crystallin expression.

Crystallins and neuroinflammation: The glial side of the story

BACKGROUND

There is an abundance of evidence to support the association of damaging neuroinflammation and neurodegeneration across a multitude of diseases. One of the links between these pathological phenomena is the role of chaperone proteins as both neuroprotective and immune-regulatory agents.

SCOPE OF REVIEW

Chaperone proteins are highly expressed at sites of neuroinflammation both in glial cells and in the injured neurons that initiate the immune response. For this reason, the use of chaperones as treatment for various diseases associated with neuroinflammation is a highly active area of investigation. This review explores the various ways that the small heat shock protein chaperones, α-crystallins, can affect glial cell function with a specific focus on their implication in the inflammatory response associated with neurodegenerative disorders, and their potential as therapeutic treatment.

MAJOR CONCLUSIONS

Although the mechanisms are still under investigation, a clear link has now been established between alpha-crystallins and neuroinflammation, especially through their roles in microglial and macroglial cells. Interestingly, similar to inflammation in itself, crystallins can have a beneficial or detrimental impact on the CNS based on the context and duration of the condition.

GENERAL SIGNIFICANCE

Overall this review points out the novel roles that chaperones such as alpha-crystallins can play outside of the classical protein folding pathways, and their potential in the development of new therapies for the treatment of neuroinflammatory/neurodegenerative diseases. This article is part of a Special Issue entitled Crystallin Biochemistry in Health and Disease.

Small heat-shock proteins: important players in regulating cellular proteostasis

Small heat-shock proteins (sHsps) are a diverse family of intra-cellular molecular chaperone proteins that play a critical role in mitigating and preventing protein aggregation under stress conditions such as elevated temperature, oxidation and infection. In doing so, they assist in the maintenance of protein homeostasis (proteostasis) thereby avoiding the deleterious effects that result from loss of protein function and/or protein aggregation. The chaperone properties of sHsps are therefore employed extensively in many tissues to prevent the development of diseases associated with protein aggregation. Significant progress has been made of late in understanding the structure and chaperone mechanism of sHsps. In this review, we discuss some of these advances, with a focus on mammalian sHsp hetero-oligomerisation, the mechanism by which sHsps act as molecular chaperones to prevent both amorphous and fibrillar protein aggregation, and the role of post-translational modifications in sHsp chaperone function, particularly in the context of disease.

Humoral response against small heat shock proteins in Parkinson's disease

Introduction

In the light of evidence for the increased heat shock proteins (HSP) expression in neurodegenerative disorders, the presence of the adaptive humoral response of the immune system can be expected. The aim of the study was to check whether Parkinson’s disease (PD) has the ability to elicit immune response against small heat shock proteins.

Methods

IgG and IgM autoantibodies against alpha B-crystallin were assessed in 26 PD patients 26 healthy subjects. For the assessment of anti-HSP IgG autoantibodies serum samples from 31 parkinsonian patients and 31 healthy control subjects were collected. Serum samples from PD patients and healthy control subjects were collected twice, at baseline and after mean of 13 months follow up.

Results

Both IgM and IgG autoantibodies against alpha ß-crystallin in PD patients were significantly higher compared to healthy controls (p<0.05). We also found statistically significant increase in antibodies titers against alpha ß-crystallin over the time of 13 months, both for IgG (p = 0.021) and for IgM (p<0.0001). Additionally, PD patients presented higher levels of anti-HSP IgG autoantibodies than healthy controls (p = 0.02).

Conclusions

Increase of IgG and IgM autoantibodies against alpha B-crystallin in PD patients over time may suggest their involvement in the disease pathogenesis and progression. Further studies are required to confirm the role of this antibody as a biomarker of the disease progression.

Bioactive TTR105-115-based amyloid fibrils reduce the viability of mammalian cells

A growing number of protein-based fibrous biomaterials have been produced with a cross-β amyloid core yet the long-term effect of these materials on cell viability and the influence of core and non-core protein sequences on viability is not well understood. Here, synthetic bioactive TTR1-RGD and control TTR1-RAD or TTR1 fibrils were used to test the response of mammalian cells. At high fibril concentrations cell viability was reduced, as assessed by mitochondrial reduction assays, lactate dehydrogenase membrane integrity assays and apoptotic biomarkers. This reduction occurred despite the high density of RGD cell adhesion ligands and use of cells displaying integrin receptors. Cell viability was affected by fibril size, maturity and whether fibrils were added to the cell media or as a pre-coated surface layer. These findings show that while cells initially interact well with synthetic fibrils, cellular integrity can be compromised over longer periods of time, suggesting a better understanding of the role of core and non-core residues in determining cellular interactions is required before TTR1-based fibrils are used as biomaterials.

Interaction of amyloid inhibitor proteins with amyloid beta peptides: insight from molecular dynamics simulations

Knowledge of the detailed mechanism by which proteins such as human αB- crystallin and human lysozyme inhibit amyloid beta (Aβ) peptide aggregation is crucial for designing treatment for Alzheimer's disease. Thus, unconstrained, atomistic molecular dynamics simulations in explicit solvent have been performed to characterize the Aβ_17–42 assembly in presence of the αB-crystallin core domain and of lysozyme. Simulations reveal that both inhibitor proteins compete with inter-peptide interaction by binding to the peptides during the early stage of aggregation, which is consistent with their inhibitory action reported in experiments. However, the Aβ binding dynamics appear different for each inhibitor. The binding between crystallin and the peptide monomer, dominated by electrostatics, is relatively weak and transient due to the heterogeneous amino acid distribution of the inhibitor surface. The crystallin-bound Aβ oligomers are relatively long-lived, as they form more extensive contact surface with the inhibitor protein. In contrast, a high local density of arginines from lysozyme allows strong binding with Aβ peptide monomers, resulting in stable complexes. Our findings not only illustrate, in atomic detail, how the amyloid inhibitory mechanism of human αB-crystallin, a natural chaperone, is different from that of human lysozyme, but also may aid de novo design of amyloid inhibitors.

SEVI, the semen enhancer of HIV infection along with fragments from its central region, form amyloid fibrils that are toxic to neuronal cells

Semen-derived enhancer of viral infection (SEVI) is the term given to the amyloid fibrils formed by a 39-amino acid fragment (PAP248-286) of prostatic acidic phosphatase (PAP) found in human semen. SEVI enhances human immunodeficiency virus (HIV) infectivity by four to five orders of magnitude (Münch et al., 2007). Here, we show by various biophysical techniques including Thioflavin T fluorescence, circular dichroism spectroscopy and transmission electron microscopy that fragments encompassing the central region of SEVI, i.e. PAP248-271 and PAP257-267, form fibrils of similar morphology to SEVI. Our results show that the central region, residues PAP267-271, is crucially important in promoting SEVI fibril formation. Furthermore, SEVI and fibrillar forms of these peptide fragments are toxic to neuronal pheochromocytoma 12 cells but not to epithelial colon carcinoma cells. These findings imply that although SEVI assists in the attachment of HIV-1 to immune cells, it may not facilitate HIV entry by damaging the epithelial cell layer that presents a barrier to the HIV.

Cell biological roles of αB-crystallin

αB-crystallin, also called HspB5, is a molecular chaperone able to interact with unfolding proteins. By interacting, it inhibits further unfolding, thereby preventing protein aggregation and allowing ATP-dependent chaperones to refold the proteins. αB-crystallin belongs to the family of small heat-shock proteins (sHsps), which in humans consists of 10 different members. The protein forms large oligomeric complexes, containing up to 40 or more subunits, which in vivo consist of heterooligomeric complexes formed by a mixture of αB-crystallin and other sHsps. αB-crystallin is highly expressed in the lens and to a lesser extent in several other tissues, among which heart, skeletal muscle and brain. αB-crystallin plays a role in several cellular processes, such as signal transduction, protein degradation, stabilization of cytoskeletal structures and apoptosis. Mutations in the αB-crystallin gene can have detrimental effects, leading to pathologies such as cataract and cardiomyopathy. This review describes the biological roles of αB-crystallin, with a special focus on its function in the eye lens, heart muscle and brain. In addition its therapeutic potential is discussed.

Gallic acid is the major component of grape seed extract that inhibits amyloid fibril formation

Many protein misfolding diseases, for example, Alzheimer's, Parkinson's and Huntington's, are characterised by the accumulation of protein aggregates in an amyloid fibrillar form. Natural products which inhibit fibril formation are a promising avenue to explore as therapeutics for the treatment of these diseases. In this study we have shown, using in vitro thioflavin T assays and transmission electron microscopy, that grape seed extract inhibits fibril formation of kappa-casein (κ-CN), a milk protein which forms amyloid fibrils spontaneously under physiological conditions. Among the components of grape seed extract, gallic acid was the most active component at inhibiting κ-CN fibril formation, by stabilizing κ-CN to prevent its aggregation. Concomitantly, gallic acid significantly reduced the toxicity of κ-CN to pheochromocytoma12 cells. Furthermore, gallic acid effectively inhibited fibril formation by the amyloid-beta peptide, the putative causative agent in Alzheimer's disease. It is concluded that the gallate moiety has the fibril-inhibitory activity.

Invited review: Caseins and the casein micelle: their biological functions, structures, and behavior in foods

A typical casein micelle contains thousands of casein molecules, most of which form thermodynamically stable complexes with nanoclusters of amorphous calcium phosphate. Like many other unfolded proteins, caseins have an actual or potential tendency to assemble into toxic amyloid fibrils, particularly at the high concentrations found in milk. Fibrils do not form in milk because an alternative aggregation pathway is followed that results in formation of the casein micelle. As a result of forming micelles, nutritious milk can be secreted and stored without causing either pathological calcification or amyloidosis of the mother's mammary tissue. The ability to sequester nanoclusters of amorphous calcium phosphate in a stable complex is not unique to caseins. It has been demonstrated using a number of noncasein secreted phosphoproteins and may be of general physiological importance in preventing calcification of other biofluids and soft tissues. Thus, competent noncasein phosphoproteins have similar patterns of phosphorylation and the same type of flexible, unfolded conformation as caseins. The ability to suppress amyloid fibril formation by forming an alternative amorphous aggregate is also not unique to caseins and underlies the action of molecular chaperones such as the small heat-shock proteins. The open structure of the protein matrix of casein micelles is fragile and easily perturbed by changes in its environment. Perturbations can cause the polypeptide chains to segregate into regions of greater and lesser density. As a result, the reliable determination of the native structure of casein micelles continues to be extremely challenging. The biological functions of caseins, such as their chaperone activity, are determined by their composition and flexible conformation and by how the casein polypeptide chains interact with each other. These same properties determine how caseins behave in the manufacture of many dairy products and how they can be used as functional ingredients in other foods.

Abnormally upregulated αB-crystallin was highly coincidental with the astrogliosis in the brains of scrapie-infected hamsters and human patients with prion diseases

αB-crystallin is a member of the small heat shock protein family constitutively presenting in brains at a relatively low level. To address the alteration of αB-crystallin in prion disease, the αB-crystallin levels in the brains of scrapie agent 263 K-infected hamsters were analyzed. The levels of αB-crystallin were remarkably increased in the brains of 263 K-infected hamsters, showing a time-dependent manner along with incubation time. Immunohistochemical (IHC) and immunofluorescent (IFA) assays illustrated more αB-crystallin-positive signals in the regions of the cortex and thalamus containing severe astrogliosis. Double-stained IFA verified that the αB-crystallin signals colocalized with the enlarged glial fibrillary acidic protein-positive astrocytes, but not with neuronal nuclei-positive cells. IHC and IFA of the serial brain sections of infected hamsters showed no colocalization and correlation between PrP(Sc) deposits and αB-crystallin increase. Moreover, increased αB-crystallin deposits were observed in the brain sections of parietal lobe of a sporadic Creutzfeldt-Jakob disease (sCJD) case, parietal lobe and thalamus of a G114V genetic CJD case, and thalamus of a fatal family insomnia (FFI) case, but not in a parietal lobe of FFI where only very mild astrogliosis was addressed. Additionally, the molecular interaction between αB-crystallin and PrP was only observed in the reactions of recombinant proteins purified from Escherichia coli, but not either in that of brain homogenates or in that of the cultured cell lysates expressing human PrP and αB-crystallin. Our data indicate that brain αB-crystallin is abnormally upregulated in various prion diseases, which is coincidental with astrogliosis. Direct interaction between αB-crystallin and PrP seems not to be essential during the pathogenesis of prion infection.

Monitoring the interaction between β2-microglobulin and the molecular chaperone αB-crystallin by NMR and mass spectrometry: αB-crystallin dissociates β2-microglobulin oligomers

The interaction at neutral pH between wild-type and a variant form (R3A) of the amyloid fibril-forming protein β2-microglobulin (β2m) and the molecular chaperone αB-crystallin was investigated by thioflavin T fluorescence, NMR spectroscopy, and mass spectrometry. Fibril formation of R3Aβ2m was potently prevented by αB-crystallin. αB-crystallin also prevented the unfolding and nonfibrillar aggregation of R3Aβ2m. From analysis of the NMR spectra collected at various R3Aβ2m to αB-crystallin molar subunit ratios, it is concluded that the structured β-sheet core and the apical loops of R3Aβ2m interact in a nonspecific manner with the αB-crystallin. Complementary information was derived from NMR diffusion coefficient measurements of wild-type β2m at a 100-fold concentration excess with respect to αB-crystallin. Mass spectrometry acquired in the native state showed that the onset of wild-type β2m oligomerization was effectively reduced by αB-crystallin. Furthermore, and most importantly, αB-crystallin reversibly dissociated β2m oligomers formed spontaneously in aged samples. These results, coupled with our previous studies, highlight the potent effectiveness of αB-crystallin in preventing β2m aggregation at the various stages of its aggregation pathway. Our findings are highly relevant to the emerging view that molecular chaperone action is intimately involved in the prevention of in vivo amyloid fibril formation.

Human prefoldin inhibits amyloid-β (Aβ) fibrillation and contributes to formation of nontoxic Aβ aggregates

Amyloid-β (Aβ) peptides represent key players in the pathogenesis of Alzheimer's disease (AD), and mounting evidence indicates that soluble Aβ oligomers mediate the toxicity. Prefoldin (PFD) is a molecular chaperone that prevents aggregation of misfolded proteins. Here we investigated the role of PFD in Aβ aggregation. First, we demonstrated that PFD is expressed in mouse brain by Western blotting and immunohistochemistry and found that PFD is upregulated in AD model APP23 transgenic mice. Then we investigated the effect of recombinant human PFD (hPFD) on Aβ(1-42) aggregation in vitro and found that hPFD inhibited Aβ fibrillation and induced formation of soluble Aβ oligomers. Interestingly, cell viability measurements using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay showed that Aβ oligomers formed by hPFD were 30-40% less toxic to cultured rat pheochromocytoma (PC12) cells or primary cortical neurons from embryonic C57BL/6CrSlc mice than previously reported Aβ oligomers (formed by archaeal PFD) and Aβ fibrils (p < 0.001). Thioflavin T measurements and immunoblotting indicated different structural properties for the different Aβ oligomers. Our findings show a relation between cytotoxicity of Aβ oligomers and structure and suggest a possible protective role of PFD in AD.

Amyloid-β oligomers are sequestered by both intracellular and extracellular chaperones

The aberrant aggregation of the amyloid-β peptide into β-sheet rich, fibrillar structures proceeds via a heterogeneous ensemble of oligomeric intermediates that have been associated with neurotoxicity in Alzheimer's disease (AD). Of particular interest in this context are the mechanisms by which molecular chaperones, part of the primary biological defenses against protein misfolding, influence Aβ aggregation. We have used single-molecule fluorescence techniques to compare the interactions between distinct aggregation states (monomers, oligomers, and amyloid fibrils) of the AD-associated amyloid-β(1-40) peptide, and two molecular chaperones, both of which are upregulated in the brains of patients with AD and have been found colocalized with Aβ in senile plaques. One of the chaperones, αB-crystallin, is primarily found inside cells, while the other, clusterin, is predominantly located in the extracellular environment. We find that both chaperones bind to misfolded oligomeric species and form long-lived complexes, thereby preventing both their further growth into fibrils and their dissociation. From these studies, we conclude that these chaperones have a common mechanism of action based on sequestering Aβ oligomers. This conclusion suggests that these chaperones, both of which are ATP-independent, are able to inhibit potentially pathogenic Aβ oligomer-associated processes whether they occur in the extracellular or intracellular environment.

Novel roles for α-crystallins in retinal function and disease

α-Crystallins are key members of the superfamily of small heat shock proteins that have been studied in detail in the ocular lens. Recently, novel functions for α-crystallins have been identified in the retina and in the retinal pigmented epithelium (RPE). αB-Crystallin has been localized to multiple compartments and organelles including mitochondria, golgi apparatus, endoplasmic reticulum and nucleus. α-Crystallins are regulated by oxidative and endoplasmic reticulum stress, and inhibit apoptosis-induced cell death. α-Crystallins interact with a large number of proteins that include other crystallins, and apoptotic, cytoskeletal, inflammatory, signaling, angiogenic, and growth factor molecules. Studies with RPE from αB-crystallin deficient mice have shown that αB-crystallin supports retinal and choroidal angiogenesis through its interaction with vascular endothelial growth factor. αB-Crystallin has also been shown to have novel functions in the extracellular space. In RPE, αB-crystallin is released from the apical surface in exosomes where it accumulates in the interphotoreceptor matrix and may function to protect neighboring cells. In other systems administration of exogenous recombinant αB-crystallin has been shown to be anti-inflammatory. Another newly described function of αB-crystallin is its ability to inhibit β-amyloid fibril formation. α-Crystallin minichaperone peptides have been identified that elicit anti-apoptotic function in addition to being efficient chaperones. Generation of liposomal particles and other modes of nanoencapsulation of these minipeptides could offer great therapeutic advantage in ocular delivery for a wide variety of retinal degenerative, inflammatory and vascular diseases including age-related macular degeneration and diabetic retinopathy.

Methionine oxidation enhances κ-casein amyloid fibril formation

The effects of protein oxidation, for example of methionine residues, are linked to many diseases, including those of protein misfolding, such as Alzheimer's disease. Protein misfolding diseases are characterized by the accumulation of insoluble proteinaceous aggregates comprised mainly of amyloid fibrils. Amyloid-containing bodies known as corpora amylacea (CA) are also found in mammary secretory tissue, where their presence slows milk flow. The major milk protein κ-casein readily forms amyloid fibrils under physiological conditions. Milk exists in an extracellular oxidizing environment. Accordingly, the two methionine residues in κ-casein (Met(95) and Met(106)) were selectively oxidized and the effects on the fibril-forming propensity, cellular toxicity, chaperone ability, and structure of κ-casein were determined. Oxidation resulted in an increase in the rate of fibril formation and a greater level of cellular toxicity. β-Casein, which inhibits κ-casein fibril formation in vitro, was less effective at suppressing fibril formation of oxidized κ-casein. The ability of κ-casein to prevent the amorphous aggregation of target proteins was slightly enhanced upon methionine oxidation, which may arise from the protein's greater exposed surface hydrophobicity. No significant changes to κ-casein's intrinsically disordered structure occurred upon oxidation. The enhanced rate of fibril formation of oxidized κ-casein, coupled with the reduced chaperone ability of β-casein to prevent this aggregation, may affect casein-casein interaction within the casein micelle and thereby promote κ-casein aggregation and contribute to the formation of CA.