Solubility and Supersaturation-Dependent Protein Misfolding Revealed by Ultrasonication

Although alcohols are useful cosolvents for producing amyloid fibrils, the underlying mechanism of alcohol-dependent fibrillation is unclear. We studied the alcohol-induced fibrillation of hen egg-white lysozyme at various concentrations of ethanol, 2,2,2-trifluoroethanol (TFE), and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). Under the conditions where the alcohol-denatured lysozyme retained metastability, ultrasonication effectively triggered fibrillation. The optimal alcohol concentration depended on the alcohol species. HFIP showed a sharp maximum at 12–16%. For TFE, a broad maximum at 40–80% was observed. Ethanol exhibited only an increase in fibrillation above 60%. These profiles were opposite to the equilibrium solubility of lysozyme in water/alcohol mixtures. The results indicate that although fibrillation is determined by solubility, supersaturation prevents conformational transitions and ultrasonication is highly effective in minimizing an effect of supersaturation. We propose an alcohol-dependent protein misfolding funnel useful for examining amyloidogenicity. This misfolding funnel will apply to fibrillation under physiological conditions where biological environments play important roles in decreasing the solubility

α‑1‑<i>C</i>‑Butyl-1,4-dideoxy-1,4-imino‑l‑arabinitol as a Second-Generation Iminosugar-Based Oral α‑Glucosidase Inhibitor for Improving Postprandial Hyperglycemia

We report on the synthesis and the biological evaluation of a series of α-1-<i>C</i>-alkylated 1,4-dideoxy-1,4-imino-l-arabinitol (LAB) derivatives. The asymmetric synthesis of the derivatives was achieved by asymmetric allylic alkylation, ring-closing metathesis, and Negishi cross-coupling as key reactions. α-1-<i>C</i>-Butyl-LAB is a potent inhibitor of intestinal maltase, isomaltase, and sucrase, with IC₅₀ values of 0.13, 4.7, and 0.032 μM, respectively. Matrix-assisted laser desorption ionization time-of-flight mass spectrometric analysis revealed that this compound differs from miglitol in that it does not influence oligosaccharide processing and the maturation of glycoproteins. A molecular docking study of maltase-glucoamylase suggested that the interaction modes and the orientations of α-1-<i>C</i>-butyl-LAB and miglitol are clearly different. Furthermore, α-1-<i>C</i>-butyl-LAB strongly suppressed postprandial hyperglycemia at an early phase, similar to miglitol in vivo. It is noteworthy that the effective dose was about 10-fold lower than that for miglitol. α-1-<i>C</i>-Butyl-LAB therefore represents a new class of promising compounds that can improve postprandial hyperglycemia