Amyloid fibril formation by native and modified bovine β-lactoglobulins proceeds through unfolded form of proteins: A comparative study

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.

Synthesis and in vitro quantification of amyloid fibrils by barbituric and thiobarbituric acid-based chromene derivatives

Neurodegenerative disease is caused by the abnormal build-up of proteins in and around cells called amyloid. The amyloid fibril formation and its mechanism have been investigated with various techniques, including dye-binding assay. Thioflavin T (ThT) has been one of the most widely used dyes for quantifying amyloid deposits, but ThT has a weak fluorescence signal especially at low concentration of amyloid fibrils, low lipophilicity and positive charge that makes it unable to cross the blood-brain barrier (BBB) to detect amyloid fibrils in vivo. Hence, there is a strong motivation for designing and developing the new compounds for in vitro amyloid quantification and in vivo amyloid imaging. The need for new probes to detect amyloid fibrils, especially within the cell, is highlighted by the fact that an accurate understanding of the molecular details of amyloid fibril formation is required to design and develop strategies for controlling the amyloid formation, and this needs more reliable probes for amyloid identification. In this work, we synthesized and applied barbituric and thiobarbituric acid-based chromene derivatives, as new fluorescent dyes to quantitatively detect the amyloid fibrils of bovine serum albumin (BSA) and human insulin in comparison with native soluble proteins or amorphous aggregation. Our results showed that among the 14 synthesized compounds, five compounds 4a, 4h, 4j, 4k, and 4l could selectively and specifically bind to amyloid fibrils while other compounds demonstrated a low-affinity binding. Furthermore, according to the cell viability experiment, compounds 4a, 4j and 4l at low concentration of compounds are not toxic, especially compound 4j which could be used as a suitable candidate for in vivo study. Further studies are needed to determine all the properties of compounds, especially in vivo experiments.

Rational Design of Amyloid-Like Fibrillary Structures for Tailoring Food Protein Techno-Functionality and Their Potential Health Implications

To control and enhance protein functionality is a major challenge for food scientists. In this context, research on food protein fibril formation, especially amyloid fibril formation, holds much promise. We here first provide a concise overview of conditions, which affect amyloid formation in food proteins. Particular attention is directed towards amyloid core regions because these sequences promote ordered aggregation. Better understanding of this process will be key to tailor the fibril formation process. Especially seeding, that is, adding preformed protein fibrils to protein solutions to accelerate fibril formation holds promise to tailor aggregation and fibril techno-functionality. Some studies have already indicated that food protein fibrillation indeed improves their techno-functionality. However, much more research is necessary to establish whether protein fibrils are useful in complex food systems and whether and to what extent they resist food processing unit operations. In this review the effect of amyloid formation on gelation, interfacial properties, foaming, and emulsification is discussed. Despite their prevalent role as functional structures, amyloids also receive a lot of attention due to their association with protein deposition diseases, prompting us to thoroughly investigate the potential health impact of amyloid-like aggregates in food. A literature review on the effect of the different stages of the human digestive process on amyloid toxicity leads us to conclude that food-derived amyloid fibrils (even those with potential pathogenic properties) very likely have minimal impact on human health. Nevertheless, prior to wide-spread application of the technology, it is highly advisable to further verify the lack of toxicity of food-derived amyloid fibrils.

Chaperone-like food components: from basic concepts to food applications

The significance of chaperones in preventing protein aggregation including amyloid fibril formation has been extensively documented in the biological field, but there is limited research on the potential effect of chaperone-like molecules on food protein functionality and food quality.

Effect of Oxidation and Protein Unfolding on Cross-Linking of β-Lactoglobulin and α-Lactalbumin

Oxidation and heat treatment can initiate changes in the amino acid composition, structure, solubility, hydrophobicity, conformation, function, and susceptibility to proteolysis of proteins. These can result in adverse consequences for mammals, plants, foodstuffs, and pharmaceuticals. This study investigated whether and how individual or combined treatment with heat, a commonly encountered factor in industrial processing, and H₂O₂ alters the structure and composition of two major milk whey proteins, α-lactalbumin and β-lactoglobulin, and mixtures of these. Thermal treatment induced reducible cross-links in isolated β-lactoglobulin, but not isolated α-lactalbumin under the conditions employed. Cross-linking occurred at lower temperatures and to a greater extent in the presence of low concentrations of H₂O₂. H₂O₂ did not induce cross-linking in the absence of heat. Mixtures of α-lactalbumin and β-lactoglobulin showed similar behavior, except that mixed α-lactalbumin-β-lactoglobulin dimers were detected. Cross-linking was associated with formation of sulfenic acids (RS-OH species), oxidation of methionine residues, cleavage of disulfide bonds in α-lactalbumin, altered conformation of disulfide bonds in β-lactoglobulin, alterations in the fluorescence intensity and maximum emission wavelength of endogenous tryptophan residues, and binding of the hydrophobic probe 8-anilinonaphthalenesulfonate. These data are consistent with increased unfolding and subsequent aggregation of the protein, with these changes being maximized in the presence of both heat and H₂O₂. The enhanced aggregation detected with H₂O₂ is consistent with additional pathways to aggregation above that induced by heat alone. These mechanistic insights provide potential strategies for modulating the extent and nature of protein modification induced by thermal and oxidant treatment.