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- Amyloid (1)
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Amyloid fibrils are polymers formed by proteins under specific conditions and in many cases they are related to pathogenesis, such as Parkinson’s and Alzheimer’s diseases. Their hallmark is the presence of a β-sheet structure. High resolution structural data on these systems as well as information gathered from multiple complementary analytical techniques is needed, from both a fundamental and a pharmaceutical perspective. Here, a previously reported de novo designed, pH-switchable coiled coil-based peptide that undergoes structural transitions resulting in fibril formation under physiological conditions has been exhaustively characterized by transmission electron microscopy (TEM), cryo-TEM, atomic force microscopy (AFM), wide-angle X-ray scattering (WAXS) and solid-state NMR (ssNMR). Overall, a unique 2-dimensional carpet-like assembly composed of large coexisiting ribbon-like, tubular and funnel-like structures with a clearly resolved protofilament substructure is observed. Whereas electron microscopy and scattering data point somewhat more to a hairpin model of β-fibrils, ssNMR data obtained from samples with selectively labelled peptides are in agreement with both, hairpin structures and linear arrangements.
Light- and small-angle neutron scattering as well as cryo-transmission electron microscopy (cryo-TEM) studies were performed to probe the structure of J-aggregates formed by a series of achiral dye molecules of the 5,5',6,6'-tetrachlorobenzimidacarbocyanine chromophore having 1,1'-dialkyl substituents combined with 3,3'-bis(4-sulfobutyl)-3,3'-bis(4-carboxybutyl) or 3,3'-bis(3-carboxypropyl) substituents. Assemblies that display a dependence on the substituents different complex supramolecular structures of nanometer-to-micrometer size have been directly visualized by cryo-TEM. The superstructures span from monomolecular layers formed by the 1,1'-diethyl-3,3'-bis(4-sulfobutyl) derivative and stacks of bilayer ribbons in the case of the 1,1'-dioctyl-3,3'-bis(4-carboxybutyl) derivative to twisted ropelike structures for the chiral aggregate of the 1,1'-dioctyl-3,3'-bis(3-carboxypropyl)-substituted chromophore.
Surfactant-induced changes of morphology of J-aggregates: Superhelix-to-tubule transformation
(2000)
The morphology of the J-aggregates formed after the addition of ionic surfactants into solutions of the 3,3'-bis(3-carboxypropyl)-5,5',6,6'-tetrachloro-1,1'-dioctylbenzimidacarbocyanine dye (C8O3) was characterized by absorption and circular dichroism spectroscopy, cryogenic temperature transmission electron microscopy, scanning force microscopy, and small-angle neutron scattering. The optical activity of the C8O3 J-aggregates, existing in aqueous solution as superhelices composed of tubular single strands, disappears upon addition of both cationic and anionic surfactants. This is accompanied by distinct spectral changes in the visible region as well as changes of the aggregates' morphology. The anionic surfactant sodium dodecyl sulfate induces the formation of single-walled tubules of 15 nm diameter and 300-600 nm length, which completely transform after several days into thick multilamellar tubes of micrometer length. The cationic surfactant trimethyltetradecylammonium bromide first produces vesicles that later transform again into tubular aggregates of nanometer thickness and micrometer length.