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by Keyword: Aggregation


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Pallarès, Irantzu, de Groot, Natalia S., Iglesias, Valentín, Sant'Anna, Ricardo, Biosca, Arnau, Fernàndez-Busquets, Xavier, Ventura, Salvador, (2018). Discovering putative prion-like proteins in Plasmodium falciparum: A computational and experimental analysis Frontiers in Microbiology 9, Article 1737

Prions are a singular subset of proteins able to switch between a soluble conformation and a self-perpetuating amyloid state. Traditionally associated with neurodegenerative diseases, increasing evidence indicates that organisms exploit prion-like mechanisms for beneficial purposes. The ability to transit between conformations is encoded in the so-called prion domains, long disordered regions usually enriched in glutamine/asparagines residues. Interestingly, Plasmodium falciparum, the parasite that causes the most virulent form of malaria, is exceptionally rich in proteins bearing long Q/N-rich sequence stretches, accounting for roughly 30% of the proteome. This biased composition suggests that these protein regions might correspond to prion-like domains (PrLDs) and potentially form amyloid assemblies. To investigate this possibility, we performed a stringent computational survey for Q/N-rich PrLDs on P. falciparum. Our data indicate that ~10% of P. falciparum protein sequences have prionic signatures, and that this subproteome is enriched in regulatory proteins, such as transcription factors and RNA-binding proteins. Furthermore, we experimentally demonstrate for several of the identified PrLDs that, despite their disordered nature, they contain inner short sequences able to spontaneously self-assemble into amyloid-like structures. Although the ability of these sequences to nucleate the conformational conversion of the respective full-length proteins should still be demonstrated, our analysis suggests that, as previously described for other organisms, prion-like proteins might also play a functional role in P. falciparum.

Keywords: Plasmodium, Protein aggregation, Amyloid, Prion, Q-N-rich sequences, Protein Disorder


Grice, L. F., Gauthier, M. E. A., Roper, K. E., Fernàndez-Busquets, X., Degnan, S. M., Degnan, B. M., (2017). Origin and evolution of the sponge aggregation factor gene family Molecular Biology and Evolution , 34, (5), 1083-1099

Although discriminating self from nonself is a cardinal animal trait, metazoan allorecognition genes do not appear to be homologous. Here, we characterize the Aggregation Factor (AF) gene family, which encodes putative allorecognition factors in the demosponge Amphimedon queenslandica, and trace its evolution across 24 sponge (Porifera) species. The AF locus in Amphimedon is comprised of a cluster of five similar genes that encode Calx-beta and Von Willebrand domains and a newly defined Wreath domain, and are highly polymorphic. Further AF variance appears to be generated through individualistic patterns of RNA editing. The AF gene family varies between poriferans, with protein sequences and domains diagnostic of the AF family being present in Amphimedon and other demosponges, but absent from other sponge classes. Within the demosponges, AFs vary widely with no two species having the same AF repertoire or domain organization. The evolution of AFs suggests that their diversification occurs via high allelism, and the continual and rapid gain, loss and shuffling of domains over evolutionary time. Given the marked differences in metazoan allorecognition genes, we propose the rapid evolution of AFs in sponges provides a model for understanding the extensive diversification of self-nonself recognition systems in the animal kingdom.

Keywords: Aggregation factor, Allorecognition, Intron phase, Polymorphism, Porifera, RNA editing


Villar-Pique, A., De Groot, N. S., Sabaté, R., Acebrón, S. P., Celaya, G., Fernàndez-Busquets, X., Muga, A., Ventura, S., (2012). The effect of amyloidogenic peptides on bacterial aging correlates with their intrinsic aggregation propensity Journal of Molecular Biology , 421, (2-3), 270-281

The formation of aggregates by misfolded proteins is thought to be inherently toxic, affecting cell fitness. This observation has led to the suggestion that selection against protein aggregation might be a major constraint on protein evolution. The precise fitness cost associated with protein aggregation has been traditionally difficult to evaluate. Moreover, it is not known if the detrimental effect of aggregates on cell physiology is generic or depends on the specific structural features of the protein deposit. In bacteria, the accumulation of intracellular protein aggregates reduces cell reproductive ability, promoting cellular aging. Here, we exploit the cell division defects promoted by the intracellular aggregation of Alzheimer's-disease-related amyloid β peptide in bacteria to demonstrate that the fitness cost associated with protein misfolding and aggregation is connected to the protein sequence, which controls both the in vivo aggregation rates and the conformational properties of the aggregates. We also show that the deleterious impact of protein aggregation on bacterial division can be buffered by molecular chaperones, likely broadening the sequential space on which natural selection can act. Overall, the results in the present work have potential implications for the evolution of proteins and provide a robust system to experimentally model and quantify the impact of protein aggregation on cell fitness.

Keywords: Amyloid fibrils, Chaperones, Escherichia coli, Inclusion bodies, Protein aggregation


Sabaté, R., Espargaró, A., de Groot, N. S., Valle-Delgado, J. J., Fernàndez-Busquets, X., Ventura, S., (2010). The role of protein sequence and amino acid composition in amyloid formation: Scrambling and backward reading of IAPP amyloid fibrils Journal of Molecular Biology , 404, (2), 337-352

The specific functional structure of natural proteins is determined by the way in which amino acids are sequentially connected in the polypeptide. The tight sequence/structure relationship governing protein folding does not seem to apply to amyloid fibril formation because many proteins without any sequence relationship have been shown to assemble into very similar β-sheet-enriched structures. Here, we have characterized the aggregation kinetics, seeding ability, morphology, conformation, stability, and toxicity of amyloid fibrils formed by a 20-residue domain of the islet amyloid polypeptide (IAPP), as well as of a backward and scrambled version of this peptide. The three IAPP peptides readily aggregate into ordered, β-sheet-enriched, amyloid-like fibrils. However, the mechanism of formation and the structural and functional properties of aggregates formed from these three peptides are different in such a way that they do not cross-seed each other despite sharing a common amino acid composition. The results confirm that, as for globular proteins, highly specific polypeptide sequential traits govern the assembly pathway, final fine structure, and cytotoxic properties of amyloid conformations.

Keywords: Amyloid formation, Islet amyloid polypeptide, Protein aggregation, Protein sequence, Retro proteins


Carulla, N., Zhou, M., Arimon, M., Gairi, M., Giralt, E., Robinson, C. V., Dobson, C. M., (2009). Experimental characterization of disordered and ordered aggregates populated during the process of amyloid fibril formation Proceedings of the National Academy of Sciences of the United States of America 106, (19), 7828-7833

Recent experimental evidence points to intermediates populated during the process of amyloid fibril formation as the toxic moieties primarily responsible for the development of increasingly common disorders such as Alzheimer's disease and type II diabetes. We describe here the application of a pulse-labeling hydrogendeuterium (HD) exchange strategy monitored by mass spectrometry (MS) and NMR spectroscopy (NMR) to characterize the aggregation process of an SH3 domain under 2 different conditions, both of which ultimately lead to well-defined amyloid fibrils. Under one condition, the intermediates appear to be largely amorphous in nature, whereas under the other condition protofibrillar species are clearly evident. Under the conditions favoring amorphous-like intermediates, only species having no protection against HD exchange can be detected in addition to the mature fibrils that show a high degree of protection. By contrast, under the conditions favoring protofibrillar-like intermediates, MS reveals that multiple species are present with different degrees of HD exchange protection, indicating that aggregation occurs initially through relatively disordered species that subsequently evolve to form ordered aggregates that eventually lead to amyloid fibrils. Further analysis using NMR provides residue-specific information on the structural reorganizations that take place during aggregation, as well as on the time scales by which they occur.

Keywords: Aggregation, HD exchange, Misfolding intermediates, PI3-SH3


Morell, M., Bravo, R., Espargaro, A., Sisquella, X., Aviles, F. X., Fernàndez-Busquets, X., Ventura, S., (2008). Inclusion bodies: Specificity in their aggregation process and amyloid-like structure Biochimica et Biophysica Acta - Molecular Cell Research , 1783, (10), 1815-1825

The accumulation of aggregated protein in the cell is associated with the pathology of many diseases and constitutes a major concern in protein production. Intracellular aggregates have been traditionally regarded as nonspecific associations of misfolded polypeptides. This view is challenged by studies demonstrating that, in vitro, aggregation often involves specific interactions. However, little is known about the specificity of in vivo protein deposition. Here, we investigate the degree of in vivo co-aggregation between two self-aggregating proteins, A beta A2 amyloid peptide and foot-and-mouth disease virus VP1 capsid protein, in prokaryotic cells. In addition, the ultrastructure of intracellular aggregates is explored to decipher whether amyloid fibrils and intracellular protein inclusions share structural properties. The data indicate that in vivo protein aggregation exhibits a remarkable specificity that depends on the establishment of selective interactions and results in the formation of oligomeric and fibrillar structures displaying amyloid-like properties. These features allow prokaryotic A beta A2 intracellular aggregates to act as effective seeds in the formation of A beta A2 amyloid fibrils. overall, our results suggest that conserved mechanisms underlie protein aggregation in different organisms. They also have important implications for biotechnological and biomedical applications of recombinant polypeptides.

Keywords: Protein aggregation, Inclusion bodies, Conformational diseases, Amyloid fibrils, Protein folding


Olmedo, Ivonne, Araya, Eyleen, Sanz, Fausto, Medina, Elias, Arbiol, Jordi, Toledo, Pedro, Àlvarez-Lueje, Alejandro, Giralt, Ernest, Kogan, Marcelo J., (2008). How changes in the sequence of the peptide CLPFFD-NH2 can modify the conjugation and stability of gold nanoparticles and their affinity for beta-amyloid fibrils Bioconjugate Chemistry , 19, (6), 1154-1163

In a previous work, we studied the interaction of β-amyloid fibrils (Aβ) with gold nanoparticles (AuNP) conjugated with the peptide CLPFFD-NH2. Here, we studied the effect of changing the residue sequence of the peptide CLPFFD-NH2 on the efficiency of conjugation to AuNP, the stability of the conjugates, and the affinity of the conjugates to the Aβ fibrils. We conjugated the AuNP with CLPFFD-NH2 isomeric peptides (CDLPFF-NH2 and CLPDFF-NH2) and characterized the resulting conjugates with different techniques including UV−Vis, TEM, EELS, XPS, analysis of amino acids, agarose gel electrophoresis, and CD. In addition, we determined the proportion of AuNP bonded to the Aβ fibrils by ICP-MS. AuNP-CLPFFD-NH2 was the most stable of the conjugates and presented more affinity for Aβ fibrils with respect to the other conjugates and bare AuNP. These findings help to better understand the way peptide sequences affect conjugation and stability of AuNP and their interaction with Aβ fibrils. The peptide sequence, the steric effects, and the charge and disposition of hydrophilic and hydrophobic residues are crucial parameters when considering the design of AuNP peptide conjugates for biomedical applications.

Keywords: Self-assembled monolayers, Aggregation, Dispersions, Adsorption, Particles, Design, Size


Arimon, M., Grimminger, V., Sanz, F., Lashuel, H. A., (2008). Hsp104 targets multiple intermediates on the amyloid pathway and suppresses the seeding capacity of A beta fibrils and protofibrils Journal of Molecular Biology , 384, (5), 1157-1173

The heat shock protein Hsp104 has been reported to possess the ability to. modulate protein aggregation and toxicity and to "catalyze" the disaggregation and recovery of protein aggregates, including amyloid fibrils, in yeast, Escherichia coli, mammalian cell cultures, and animal models of Huntington's disease and Parkinson's disease. To provide mechanistic insight into the molecular mechanisms by which Hsp104 modulates aggregation and fibrillogenesis, the effect of Hsp104 on the fibrillogenesis of amyloid beta (A(3) was investigated by characterizing its ability to interfere with oligomerization and fibrillogenesis of different species along the amyloid-formation pathway of A beta. To probe the disaggregation activity of Hsp104, its ability to dissociate preformed protofibrillar and fibrillar aggregates of A beta was assessed in the presence and in the absence of ATP. Our results show that Hsp104 inhibits the fibrillization of monomeric and protofibrillar forms of A beta in a concentration-dependent but ATP-independent manner. Inhibition of A beta fibrillization by Hsp104 is observable up to Hsp104/A beta stoichiometric ratios of 1:1000, suggesting a preferential interaction of Hsp104 with aggregation intermediates (e.g., oligomers, protofibrils, small fibrils) on the pathway of A beta amyloid formation. This hypothesis is consistent with our observations that Hsp104 (i) interacts with A beta protofibrils, (ii) inhibits conversion of protofibrils into amyloid fibrils, (iii) arrests fibril elongation and reassembly, and (iv) abolishes the capacity of protofibrils and sonicated fibrils to seed the fibrillization of monomeric A beta. Together, these findings suggest that the strong inhibition of A beta fibrillization by Hsp104 is mediated by its ability to act at different stages and target multiple intermediates on the pathway to amyloid formation.

Keywords: Amyloid formation A beta, Hsp104, Disaggregation, Alzheimer's diseases