His-tagged molecules can be attached to lipid bilayers via certain anchor lipids, a method that has been widely used for the biofunctionalization of membranes and vesicles. To observe the membrane-bound...

Arranging into well-organized fibrillar aggregate, commonly known as amyloid fibril is an inherent property of any polypeptide chain. Amyloid fibrils are associated with a number of severe human pathologies like the Alzheimer's disease, Parkinson's disease, type2 diabetes and many more. Recent studies suggest that most of the fibrils are inert and extremely stable, thus could be used for the bionanotechnological applications. As the native state is protected by evolution from aggregation under physiological condition, understanding the structure of aggregation precursor state (APS) will be of extreme importance to decode mechanism of its formation and prevention. This review article includes the recent studies of identification and characterization of possible conformations of proteins which can act as APS. The literature regarding the research in this field revealed that any conformation ranging from native-like state to completely unfolded state could be an APS. The structural characteristics of the APS depend on the protein and on its surrounding environment. From this review of literatures, we conclude that exposure of aggregation-prone segments is the requirement for amyloid fibril formation and the amyloid state seems to be the most stable known physical state of the proteins. This means all conformations of proteins with exposed aggregation-prone segments can promote intermolecular interactions and channel to amyloid fibril pathway to acquire their minimum energy state.

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Structure-based "rational" drug design strategies fail for diseases associated with intrinsically disordered proteins (IDPs). However, structural disorder allows large-amplitude spontaneous intramolecular dynamics in a protein. We demonstrate a method that exploits this dynamics to provide quantitative information about the degree of interaction of an IDP with other molecules. A candidate ligand molecule may not bind strongly, but even momentary interactions can be expected to perturb the fluctuations. We measure the amplitude and frequency of the equilibrium fluctuations of fluorescently labeled small oligomers of hIAPP (an IDP associated with type II diabetes) in a physiological solution, using nanosecond fluorescence cross-correlation spectroscopy. We show that the interterminal distance fluctuates at a characteristic time scale of 134 ± 10 ns, and 6.4 ± 0.2% of the population is in the "closed" (quenched) state at equilibrium. These fluctuations are affected in a dose-dependent manner by a series of small molecules known to reduce the toxicity of various amyloid peptides. The degree of interaction increases in the following order: resveratrol < epicatechin ∼ quercetin < Congo red < epigallocatechin 3-gallate. Such ordering can provide a direction for exploring the chemical space for finding stronger-binding ligands. We test the biological relevance of these measurements by measuring the effect of these molecules on the affinity of hIAPP for lipid vesicles and cell membranes. We find that the ability of a molecule to modulate intramolecular fluctuations correlates well with its ability to lower membrane affinity. We conclude that structural disorder may provide new avenues for rational drug design for IDPs.