pH-responsive modulation of insulin aggregation and structural transformation of the aggregates.

Over the past two decades, much information has appeared on electrostatically driven molecular mechanisms of protein self-assembly and formation of aggregates of different morphology, varying from soluble amorphous structures to highly-ordered amyloid-like fibrils. Protein aggregation represents a special tool in biomedicine and biotechnology to produce biological materials for a wide range of applications. This has awakened interest in identification of pH-triggered regulators of transformation of aggregation-prone proteins into structures of higher order.

Can aggregation of insulin govern its fate in the intestine? Implications for oral delivery of the drug.

The objective of this study is to elucidate the role of low-molecular weight biogenic agents, resembling dietary-derived products naturally occurring in the intestine, in the regulation of transformations of soluble aggregation-prone insulin into aggregates of higher order. In the course of model experiments, a striking potential of the amino acids L-arginine (Arg) and L-lysine (Lys) and a number of positively charged peptides to induce formation of heterogenic supramolecular structures of insulin was demonstrated under environment conditions where the protein aggregation in their absence was not observed. This phenomenon is assumed to be essential for elaboration of strategies of oral delivery of insulin to diabetic patients supplemented by controlling the pH values of the intestinal environment where the drug is released.

L-arginine induces protein aggregation and transformation of supramolecular structures of the aggregates.

Protein misfolding, self-assembly, and aggregation are an essential problem in cell biology, biotechnology, and biomedicine. The protein aggregates are very different morphologically varying from soluble amorphous aggregates to highly ordered amyloid-like fibrils. The objective of this study was to elucidate the role of the amino acid L-arginine (Arg), a widely used suppressor of protein aggregation, in the regulation of transformations of soluble aggregation-prone proteins into supramolecular structures of higher order.

Transient transformation of oligomeric structure of alpha-crystallin during its chaperone action.

New evidence for dynamic behavior and flexible oligomeric structure of the molecular chaperone α-crystallin is presented. Based on the results of laser dynamic light scattering, centrifugal ultrafiltration, size exclusion chromatography, analytical ultracentrifugation and electrophoresis in polyacrylamide gel, addition of α-crystallin to fully reduced α-lactalbumin, used as a model protein substrate, at the stage of its start aggregate formation results in dissociation of multimeric structure of α-crystallin. In addition to large oligomers, transient low-sized assemblies are formed with the apparent molecular mass of 50-55 kDa that corresponds to the α-crystallin dimeric form associated with destabilized monomeric α-lactalbumin.

Formation of supramolecular structures of a native-like protein in the presence of amphiphilic peptides: Variations in aggregate morphology.

A striking potential of the amphiphilic dipeptides, Arg-Phe or Asp-Phe, to induce aggregation of a model protein, alcohol dehydrogenase in its native-like state, has been demonstrated under physiologically relevant conditions, using dynamic light scattering, fluorescence spectroscopy, circular dichroism, transmission electron- and atomic force microscopy. The peptide action resulted in accumulation of a variety of morphologically distinct supramolecular structures profoundly differing from those generated by the heat-induced aggregation at the early stages of the process, when amyloid fibril assemblies were not detectable. The biogenic amphiphilic agents are suggested to act as regulators of structural transformations of native-like proteins.