Nanopatterned Polymer Surface Modulates Twist Polymorphism in a Single Amyloid Fibril

Supramolecular organization of Cytochrome-C into quantum-dot decorated macromolecular network under pH and thermal stress

The holo form of Cytochrome-C which is involved in the electron transfer chain of aerobic and anaerobic respiration remains structurally intact by its complex with heme. However, when a prolonged thermal and pH stress was applied, heme was found to abruptly dissociate from the holo protein, resulting in complete collapse of the three-dimensional functional structure. Interestingly, two distinct structures were formed as the consequence of the dissociation event: (i) A macromolecular amyloid-network formed by the collapsed protein fragments, generated by self-oxidation, and (ii) Fe-containing Quantum-Dots (FeQDs) with 2-3 nm diameter formed by heme reorganization. Further adding to intrigue, the FeQDs were re-adsorbed on the surface of the amyloid network leading to FeQD-decorated macromolecular amyloid matrix. The heme-interactant Met80, constituting the amyloidogenic region, initiates the amylogenic cascade, and gradual exposure of Trp59 synergistically emit intrinsic fluorescence alongside FeQDs. The development of the aforementioned events were probed through a multitude of biophysical, chemical and computational analyses like ThT/ANS/intrinsic fluorescence assays, CD-spectroscopy, FETEM/STEM/elemental mapping, Foldamyloid/Foldunfold/Isunstruct/H-protection/LIGplot analyses, etc. The FeQD-decorated amyloid-network was found to exhibit gel-like property, which supported the growth of BHK-21 fibroblast without cytotoxicity. Further studies on FeQD-decorated Cytochrome C amyloid network might open possibilities to design advanced biomaterial for diverse biological applications.

Self-Coiling of Single-Stranded Protofibrils into Rings: A Pathway of Alzheimer's β-Peptide Amyloidosis on Lipid Membranes

An amyloidosis pathway of Alzheimer's β-peptide Aβ40 on lipid membranes, the self-coiling of single-stranded protofibrils into thermodynamically stable ring structures, is uncovered. Distinct from Aβ amyloid structures reported previously, the coiled rings observed here exhibit a narrow distribution of diameters centered at ∼170 nm and their circumference thicknesses increase as a longer single-stranded protofibril wraps around the ring, indicating the coaxial loop-by-loop winding of individual protofibrils. Such self-coiling is dominated by elastic properties of the flexible protofibrils subject to thermal fluctuations and surface interactions, as supported by an entropic elasticity model from polymer physics concepts. This work not only provides insights into the fundamental physics of Alzheimer's β-peptide amyloidosis but also is useful for designing amyloid filament materials.