The main hypothesis for prion diseases is that the cellular protein (PrP
C) can be altered into a misfolded,
β-sheet-rich isoform (PrP
Sc), which undergoes aggregation and triggers the onset of ...transmissible spongiform encephalopathies. Here, we investigate the effects of amino-terminal deletion mutations, rPrP
Δ51–90 and rPrP
Δ32–121, on the stability and the packing properties of recombinant murine PrP. The region lacking in rPrP
Δ51–90 is involved physiologically in copper binding and the other construct lacks more amino-terminal residues (from 32 to 121). The pressure stability is dramatically reduced with decreasing N-domain length and the process is not reversible for rPrP
Δ51–90 and rPrP
Δ32–121, whereas it is completely reversible for the wild-type form. Decompression to atmospheric pressure triggers immediate aggregation for the mutants in contrast to a slow aggregation process for the wild-type, as observed by Fourier-transform infrared spectroscopy. The temperature-induced transition leads to aggregation of all rPrPs, but the unfolding temperature is lower for the rPrP amino-terminal deletion mutants. The higher susceptibility to pressure of the amino-terminal deletion mutants can be explained by a change in hydration and cavity distribution. Taken together, our results show that the amino-terminal region has a pivotal role on the development of prion misfolding and aggregation.
Transthyretin (TTR) is an amyloidogenic protein whose aggregation is responsible for several familial amyloid diseases. Here, we use FTIR to describe the secondary structural changes that take place ...when wt TTR undergoes heat- or high-pressure-induced denaturation, as well as fibril formation. Upon thermal denaturation, TTR loses part of its intramolecular
β-sheet structure followed by an increase in nonnative, probably antiparallel
β-sheet contacts (bands at 1616 and 1686
cm
−1) and in the light scattering, suggesting its aggregation. Pressure-induced denaturation studies show that even at very elevated pressures (12
kbar), TTR loses only part of its
β-sheet structure, suggesting that pressure leads to a partially unfolded species. On comparing the FTIR spectrum of the TTR amyloid fibril produced at atmospheric pressure upon acidification (pH 4.4) with the one presented by the native tetramer, we find that the content of
β-sheets does not change much upon fibrillization; however, the alignment of
β-sheets is altered, resulting in the formation of distinct
β-sheet contacts (band at 1625
cm
−1). The random-coil content also decreases in going from tetramers to fibrils. This means that, although part of the tertiary- and secondary-structure content of the TTR monomers has to be lost before fibril formation, as previously suggested, there must be a subsequent reorganization of part of the random-coil structure into a well-organized structure compatible with the amyloid fibril, as well as a readjustment of the alignment of the
β-sheets. Interestingly, the infrared spectrum of the protein recovered from a cycle of compression-decompression at pD 5, 37°C, is quite similar to that of fibrils produced at atmospheric pressure (pH 4.4), which suggests that high hydrostatic pressure converts the tetramers of TTR into an amyloidogenic conformation.
An altered form of the cellular prion protein, the PrPScor PrPRes, is implicated in the occurrence of the still untreatable transmissible spongiform encephalopathies. We have previously synthesized ...and characterized aromatic compounds that inhibit protease-resistant prion protein (PrPRes) accumulation in scrapie-infected cells. These compounds belong to different chemical classes, including acylhydrazones, chalcones and oxadiazoles. Some of the active compounds were non-toxic to neuroblastoma cells in culture and seem to possess drugable properties, since they are in agreement with the Lipinski´s rule of 5 and present desirable pharmacokinetic profiles as predicted in silico. Before the evaluation of the in vivo efficacy of the aromatic compounds in scrapie-infected mice, safety assessment in healthy mice is needed. Here we used Swiss mice to evaluate the acute toxicity profile of the six most promising anti-prionic compounds, the 2,4,5-trimethoxychalcones (J1, J8, J20 and J35) and the 1,3,4-oxadiazoles (Y13 and Y17). One single oral administration (300 mg/kg) of J1, J8, J20, J35, Y13 and Y17 or repeated intraperitoneal administration (10 mg/kg, 3 times a week, for 4 weeks) of J1, J8 and J35, did not elicit toxicity in mice. We strongly believe that the investigated trimethoxychalcones and oxadiazoles are interesting compounds to be further analyzed in vivo against prion diseases.
Although prion protein fibrils can have either parallel-in-register intermolecular β-sheet (PIRIBS) or, probably, β-solenoid architectures, the plausibility of PIRIBS architectures for the usually ...glycosylated natural prion strains has been questioned based the expectation that such glycans would not fit if stacked in-register on each monomer within a fibril. To directly assess this issue, we have added N-linked glycans to a recently reported cryo-electron microscopy-based human prion protein amyloid model with a PIRIBS architecture and performed in silico molecular dynamics studies to determine if the glycans can fit. Our results show that triantennary glycans can be sterically accommodated in-register on both N-linked glycosylation sites of each monomer. Additional simulations with an artificially mutated β-solenoid model confirmed that glycans can be accommodated when aligned with ∼4.8 Å spacing on every rung of a fibril. Altogether, we conclude that steric intermolecular clashes between glycans do not, in themselves, preclude PIRIBS architectures for prions.
Liquid–liquid phase separation (LLPS) and phase transitions (PT) of proteins, which include the formation of gel- and solid-like species, have been characterized as physical processes related to the ...pathology of conformational diseases. Nucleic acid (NA)-binding proteins related to neurodegenerative disorders and cancer were shown by us and others to experience PT modulated by different NAs. Herein, we discuss recent work on phase separation and phase transitions of two amyloidogenic proteins, i.e. the prion protein (PrP) and p53, which undergo conformational changes and aggregate upon NA interaction. The role of different NAs in these processes is discussed to shed light on the relevance of PSs and PTs for both the functional and pathological roles of these mammalian proteins.
•Proteins involved in cancer and neurodegenerative diseases undergo phase transitions.•Nucleic acids modulate prion protein and p53 phase transitions.•PrP liquid droplets evolve to gel-like species depending on the interacting NA.•p53 higher-order structures participate on cancer-promoting activities through NA binding.
Over 50% of all human cancers lose p53 function. To evaluate the role of aggregation in cancer, we asked whether wild-type (WT) p53 and the hot-spot mutant R248Q could aggregate as amyloids under ...physiological conditions and whether the mutant could seed aggregation of the wild-type form. The central domains (p53C) of both constructs aggregated into a mixture of oligomers and fibrils. R248Q had a greater tendency to aggregate than WT p53. Full-length p53 aggregated into amyloid-like species that bound thioflavin T. The amyloid nature of the aggregates was demonstrated using x-ray diffraction, electron microscopy, FTIR, dynamic light scattering, cell viabilility assay, and anti-amyloid immunoassay. The x-ray diffraction pattern of the fibrillar aggregates was consistent with the typical conformation of cross β-sheet amyloid fibers with reflexions of 4.7 Å and 10 Å. A seed of R248Q p53C amyloid oligomers and fibrils accelerated the aggregation of WT p53C, a behavior typical of a prion. The R248Q mutant co-localized with amyloid-like species in a breast cancer sample, which further supported its prion-like effect. A tumor cell line containing mutant p53 also revealed massive aggregation of p53 in the nucleus. We conclude that aggregation of p53 into a mixture of oligomers and fibrils sequestrates the native protein into an inactive conformation that is typical of a prionoid. This prion-like behavior of oncogenic p53 mutants provides an explanation for the negative dominance effect and may serve as a potential target for cancer therapy.
Abnormal phase transitions have been implicated in the occurrence of proteinopathies. Disordered proteins with nucleic acidbinding ability drive the formation of reversible micron‐sized condensates ...capable of controlling nucleic acid processing/transport. This mechanism, achieved via liquid–liquid phase separation (LLPS), underlies the formation of long‐studied membraneless organelles (e.g., nucleolus) and various transient condensates formed by driver proteins. The prion protein (PrP) is not a classical nucleic acid‐binding protein. However, it binds nucleic acids with high affinity, undergoes nucleocytoplasmic shuttling, contains a long intrinsically disordered region rich in glycines and evenly spaced aromatic residues, among other biochemical/biophysical properties of bona fide drivers of phase transitions. Because of this, our group and others have characterized LLPS of recombinant PrP. In vitro phase separation of PrP is modulated by nucleic acid aptamers, and depending on the aptamer conformation, the liquid droplets evolve to solid‐like species. Herein, we discuss recent studies and previous evidence supporting PrP phase transitions. We focus on the central role of LLPS related to PrP physiology and pathology, with a special emphasis on the interaction of PrP with different ligands, such as proteins and nucleic acids, which can play a role in prion disease pathogenesis. Finally, we comment on therapeutic strategies directed at the non‐functional phase separation that could potentially tackle prion diseases or other protein misfolding disorders.
Condensates formed by neurodegeneration‐prone proteins through liquid–liquid phase separation drive many cellular processes, from signaling at the membrane to gene expression in the nucleus. Recently, we and others have shown that prion protein (PrP) forms condensates finely controlled by physicochemical factors and ligands' concentration. Here, we discuss how PrP phase separation relates to its function and is possibly behind pathological aggregation. We also review important structural characteristics of PrP and comment on hypothetical therapies to tackle aberrant condensation. We present an integrated view of PrP phase separation ability that might contribute toward understanding the molecular basis of prion diseases.
The p53 Core Domain Is a Molten Globule at Low pH Ano Bom, Ana Paula D.; Freitas, Monica S.; Moreira, Flavia S. ...
The Journal of biological chemistry,
01/2010, Letnik:
285, Številka:
4
Journal Article
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Odprti dostop
p53 is a transcription factor that maintains genome integrity, and its function is lost in 50% of human cancers. The majority of p53 mutations are clustered within the core domain. Here, we ...investigate the effects of low pH on the structure of the wild-type (wt) p53 core domain (p53C) and the R248Q mutant. At low pH, the tryptophan residue is partially exposed to the solvent, suggesting a fluctuating tertiary structure. On the other hand, the secondary structure increases, as determined by circular dichroism. Binding of the probe bis-ANS (bis-8-anilinonaphthalene-1-sulfonate) indicates that there is an increase in the exposure of hydrophobic pockets for both wt and mutant p53C at low pH. This behavior is accompanied by a lack of cooperativity under urea denaturation and decreased stability under pressure when p53C is in acidic pH. Together, these results indicate that p53C acquires a partially unfolded conformation (molten-globule state) at low pH (5.0). The hydrodynamic properties of this conformation are intermediate between the native and denatured conformation. 1H-15N HSQC NMR spectroscopy confirms that the protein has a typical molten-globule structure at acidic pH when compared with pH 7.2. Human breast cells in culture (MCF-7) transfected with p53-GFP revealed localization of p53 in acidic vesicles, suggesting that the low pH conformation is present in the cell. Low pH stress also tends to favor high levels of p53 in the cells. Taken together, all of these data suggest that p53 may play physiological or pathological roles in acidic microenvironments.
The main hypothesis for prion diseases proposes that the cellular protein (PrP(c)) can be altered into a misfolded, beta-sheet-rich isoform (PrP(Sc)). We describe here that host nucleic acid may ...catalyze the conversion between PrP(c) and PrP(Sc) isoforms, by reducing the protein mobility and by making the protein-protein interactions more likely. We summarize the findings, focusing in the biological relevance of the catalytic action of nucleic acid.
Biomolecular condensates, membrane-less entities arising from liquid–liquid phase separation, hold dichotomous roles in health and disease. Alongside their physiological functions, these condensates ...can transition to a solid phase, producing amyloid-like structures implicated in degenerative diseases and cancer. This review thoroughly examines the dual nature of biomolecular condensates, spotlighting their role in cancer, particularly concerning the p53 tumor suppressor. Given that over half of the malignant tumors possess mutations in the TP53 gene, this topic carries profound implications for future cancer treatment strategies. Notably, p53 not only misfolds but also forms biomolecular condensates and aggregates analogous to other protein-based amyloids, thus significantly influencing cancer progression through loss-of-function, negative dominance, and gain-of-function pathways. The exact molecular mechanisms underpinning the gain-of-function in mutant p53 remain elusive. However, cofactors like nucleic acids and glycosaminoglycans are known to be critical players in this intersection between diseases. Importantly, we reveal that molecules capable of inhibiting mutant p53 aggregation can curtail tumor proliferation and migration. Hence, targeting phase transitions to solid-like amorphous and amyloid-like states of mutant p53 offers a promising direction for innovative cancer diagnostics and therapeutics.
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