Biology subjects

Ortigosa-Pascual, L.

Publications and source records attributed to Ortigosa-Pascual, L..

5 recordsLinked to original sources

bioRxiv2026

Opposing Regulation of Tau Condensation by Phosphorylation Levels and Molecular Chaperone Interactions

Aggregation of the microtubule-stabilizing protein Tau into insoluble deposits is characteristic for several neurodegenerative diseases, including Alzheimer's disease. While phosphorylated Tau (pTau) appears as a normal post-translational modification, the accumulation of hyperphosphorylated Tau aggregates represents a hallmark of these disorders. The molecular mechanisms involved in the conversion from functional Tau into pathological assemblies are still not elucidated. Here, we identified the role of phosphorylation levels on the phase separation and aggregation behavior of Tau, and how these processes can be counteracted by the molecular chaperone-like Bri2 BRICHOS domain. We found that the phosphorylation pattern modulates Tau fibrillation and enhances its droplet-formation propensity. Remarkably, Bri2 BRICHOS generally shifts Tau phase boundaries, counteracting the dense state, and inhibits Tau fibril formation, irrespectively of the degree of phosphorylation. Solution NMR results pinpointed the binding site of Bri2 BRICHOS on pTau, both in the dilute phase and droplet state, revealing an effect on specific regions and phosphorylated residues, which appear to be crucial for the formation and maintenance of the droplet state. Taken together, this study uncovered the opposing regulatory roles of phosphorylation and the anti-amyloid chaperone Bri2 BRICHOS on biomolecular condensation and fibrillation of Tau, providing detailed insights into the molecular mechanisms involved in tauopathies, which may facilitate future treatment strategies using chaperone-based inhibitors.

biophysics↗

bioRxiv2026

Errors in peptide synthesis are a source of discrepancies in Aβ42 studies

Amyloid-{beta}42 (A{beta}42) aggregation is highly sensitive to experimental conditions, making reproducibility a persistent challenge in Alzheimers disease research. Among the many variables that influence aggregation, the impact of peptide production remains poorly understood. Direct comparison of recombinant and chemically synthesised A{beta}42 prepared under carefully controlled conditions reveals that, despite following similar aggregation mechanism and forming the same predominant fibril structures, synthetic A{beta}42 aggregates more slowly and exhibits reduced seeding efficiency. Consequently, synthetic A{beta}42 produces fewer oligomeric species and displays lower cellular toxicity. Mass spectrometric analyses identify low-abundance sequence imperfections introduced during peptide synthesis as the origin of these differences. By linking synthesis-derived imperfections to variations in A{beta}42 behaviour, this work reveals a previously underappreciated source of discrepancies in amyloid studies. In addition, we provide a framework for evaluating the impact of sequence impurities on biophysical studies that are sensitive to peptide composition.

biochemistry↗

bioRxiv2026

Potent substoichiometric inhibition of alpha-synuclein aggregation by de novo oligomer-binding proteins

The intrinsically disordered, non-amyloid-{beta} component domain of -synuclein (Syn) drives aggregation in Parkinson's disease but lacks a stable epitope for structure-based drug design. We used deep learning-based protein design to generate de novo binders capturing this region in a {beta}-strand conformation. Three designs bound Syn with nanomolar affinities, with solution NMR spectroscopy supporting the intended fold. All three suppressed fibril formation at substoichiometric ratios, and fitting of aggregation kinetics resolved the microscopic steps inhibited by each. Notably, one binder preferentially engaged oligomers and inhibited secondary nucleation, both closely linked to toxicity. In cells, all three suppressed seeded Syn assembly, with the oligomer binder being the most effective. Together, these findings establish a set of molecules that target distinct aggregation intermediates and mechanistically reshape Syn assembly.

biophysics↗

bioRxiv2025

Tau catalyzes amyloid-β aggregation in a fold-dependent manner

Interactions between amyloidogenic proteins are emerging as critical drivers of neurodegenerative diseases, yet the molecular mechanisms remain poorly understood. In Alzheimers disease (AD) and chronic traumatic encephalopathy (CTE), co-deposition of tau and amyloid-{beta} (A{beta}) leads to accelerated disease progression. Here, we investigated the direct interaction between A{beta} and tau, combining in vitro reconstruction, computational modeling, and in vivo models. We show that tau aggregates with AD paired helical filament (PHF) and CTE folds catalyze the primary nucleation of A{beta}42 in a fold-specific manner, through an enzyme-like kinetic with recognition mechanisms. CTE fibrils exhibit the highest catalytic activity, also constraining A{beta}42 polymorphism. PHF and CTE tau fibrils increase A{beta}42 toxicity in SH-SY5Y neuroblastoma cells and transgenic Caenorhabditis elegans. Catalytic heterotypic interactions between amyloidogenic proteins offer new insights into the pathological mechanisms of multiple proteinopathies. The mechanisms described here may guide the structure-based design of new therapeutic agents targeting specific amyloidogenic interactions.

biochemistry↗

bioRxiv2025

On the transient interactions of α-synuclein in different dimensions

0.-Synuclein (Syn) is a neuronal protein predominantly found in the brain, whose native function seems to be associated with vesicle trafficking. While intrinsically disordered in solution, the first ca. 100 residues adopt an amphipathic -helical structure when the protein adsorbs onto membranes. Additionally, the aggregation of Syn into highly ordered {beta}-sheet rich amyloid fibrils is associated with Parkinso[n]s disease. The different regions of Syn and the interactions between them have been reported to play a key role in the behaviour of the protein in solution, its membrane binding, and its aggregation into fibrils. This study employs photo-induced cross-linking of unmodified proteins (PICUP) to capture and identify the transient contacts of Syn in different conformational states: free in solution, adsorbed to membranes, and aggregated into fibrils. By using tyrosine-to-phenylalanine mutations to block the reactivity of specific amino acid residues, we establish key cross-links in each state. In solution, we identify internal contacts between the N and C termini of monomers, as well as inter-monomer contacts between C termini in oligomers. When Syn is adsorbed to membranes, the internal cross-linking is blocked, while cross-linking between C-terminal regions persists. In fibrils, cross-linking is significantly reduced, primarily occurring between C-terminal residues of adjacent monomers. This work highlights the utility of PICUP for reporting on the transient contacts that occur on the pathways of self- and co-assembly of Syn.

biochemistry↗