Structural evolution of a yeast amyloid in vivo is shaped by chaperones

Secondary nucleation drives polymorph diversity in hIAPP amyloids

Amyloid fibrils are implicated in a myriad of human diseases. A striking observation is that fibrils extracted from diseased tissues are characterized by a restricted set of folds unique to the specific pathology. In contrast, fibrils grown in vitro exhibit extensive structural diversity, suggesting that specific environmental and biochemical mechanisms in vivo enforce structural selectivity. Here, we combine two-dimensional infrared (2D IR) spectroscopy and cryo-electron microscopy (cryo-EM) to investigate the mechanisms governing polymorph formation in the human Islet Amyloid Polypeptide (hIAPP). We demonstrate that 2D IR can resolve populations of distinct polymorphs identified by cryo-EM, enabling rapid label-free screening of conditions prior to labor-intensive microscopy screening. We find that conditions favoring secondary nucleation, such as high protein concentration, increase polymorphic diversity. Crucially, cryo-EM reveals that formed by secondary nucleation do not structurally replicate the parent template. Finally, by selectively inhibiting secondary nucleation using the C-terminal domain of the DNAJB6 chaperone, we steer aggregation toward a monomorphic state. These findings highlight the critical role of molecular chaperones in fibril polymorph selection.

Recent cryo-EM structures redefine the functional amyloid landscape.

Structural Basis of Amyloid Fibril Assembly by Plant Seed Storage Proteins

Amyloid fibrils are highly ordered protein assemblies characterized by a cross-β architecture. A wide range of proteins can adopt amyloid states, contributing to both disease-related pathology and normal physiological function. While animal-derived amyloids have been extensively examined in atomic detail, amyloid fibrils formed by plant proteins remain relatively understudied. Here we systematically assess three major seed storage proteins—oat 12S globulin, soybean 7S globulin, and rice glutelin—under harsh cooking-like conditions (pH 2, 85 °C). Oat globulin and rice glutelin readily form fibrils in both purified preparations and whole-seed extracts, whereas soybean globulin forms fibrils only in purified preparations and remains largely amorphous in whole-seed extracts. Using cryo-electron microscopy, we determine the structure of oat globulin fibrils at 3.9 Å resolution. The fibril core adopts a compact triangular architecture with pseudo-threefold symmetry and is stabilized by extensive hydrophobic and aromatic packing. Our findings establish the molecular basis of amyloid formation in plant seeds and expand the structural landscape of amyloid fibrils beyond animal and microbial systems, providing a foundation for understanding amyloid formation in plant- and food-derived proteins. Plant seed storage proteins can form amyloid fibrils under cooking-like conditions. Zhang et al. systematically compare three major plant seed storage proteins and determine the cryo-EM structures of oat globulin fibrils, providing molecular insight into amyloid assembly by plant-derived proteins.

Deletion Analysis of Phase Separation, Amyloid Formation and Prion Propagation by the Intrinsically Disordered Region of Yeast Sup35 Protein

Deletion analysis demonstrates that the N-proximal prion domain (Sup35N) of Sup35 is sufficient for chaperone-dependent prion propagation and that various regions of this domain show differential impacts on LLPS, amyloid aggregation, and prion inheritance.

Structural and Functional Plasticity of the Staphylococcus aureus Virulence-Associated Amyloid Peptide PSMα1

The findings show that bacterial virulence can be regulated through environmentally controlled transitions between protein assemblies, identifying membrane accumulation as a promising anti-virulence target.

Amyloid Polymorphism of Lysozyme Governs Cross-Seeding of Insulin Aggregation

Amyloid fibrils are highly ordered protein aggregates characterized by a conserved cross-β-sheet architecture despite originating from structurally diverse precursor proteins. Growing evidence suggests that interactions between different amyloidogenic proteins can modulate aggregation pathways through heterologous cross-seeding; however, the influence of seed polymorphism on the structure and biological properties of cross-seeded fibrils remains poorly understood. Here, we investigated the cross-seeding of native human insulin by two structurally distinct polymorphs of hen egg-white lysozyme (HEWL): flexible fibrils (FFs) and rigid fibrils (RFs). Native insulin remained stable under physiological conditions and underwent spontaneous fibrillation only under acidic conditions. In contrast, both HEWL polymorphs efficiently induced insulin aggregation at physiological pH, bypassing the nucleation barrier. Thioflavin T fluorescence, circular dichroism spectroscopy, and transmission electron microscopy revealed that lysozyme FFs templated the formation of insulin flexible fibrils (IFFs), whereas lysozyme RFs produced insulin rigid fibrils (IRFs), demonstrating that the structural characteristics of the parental HEWL polymorphs were propagated during heterologous cross-seeding. The toxicity of the resulting insulin fibrils was evaluated in SH-SY5Y neuronal cells and CCF-STTG1 astrocytes. IFFs exhibited minimal cytotoxicity and only subtle morphological alterations, whereas IRFs caused modest reductions in cell viability accompanied by more pronounced cellular damage. These findings demonstrate that the structural polymorphism of HEWL fibrils governs both the architecture and biological activity of cross-seeded insulin fibrils, highlighting amyloid polymorphism as an important determinant of heterologous amyloid propagation and a potential design principle for engineering functional amyloid-based biomaterials and protein delivery platforms.