Cosolvent effects on the fibrillation reaction of human IAPP

Abstract

Owing to the presence of various types of osmolytes in the cellular environment, this study focuses on the impact of stabilizing (TMAO and betaine) as well as destabilizing (urea) cosolvents on the aggregation and fibrillation reaction of the highly amyloidogenic islet amyloid polypeptide (IAPP). IAPP is associated with type-2 diabetes mellitus and is responsible for the disease accompanying β-cell membrane permeabilization and final β-cell loss. To reveal the impact of the cosolvents on the aggregation kinetics, conformational and morphological changes upon IAPP fibrillation, Thioflavin T fluorescence spectroscopy, atomic force microscopy and attenuated total reflection Fourier-transform infrared spectroscopy were applied. For TMAO, and less pronounced for betaine, a decrease of the growth rate of fibrils is observed, whereas the lag phase remains essentially unchanged, indicating the ability of the compatible solutes to stabilize large oligomeric and protofibrillar structures and therefore hamper fibril elongation. Conversely, urea displays concentration-dependent prolongation of the lag phase, indicating stabilization of IAPP in its unfolded monomeric state, hence leading to retardation of IAPP nuclei formation. Mixtures of urea with TMAO, and to a lesser extent with betaine, exhibit a counteractive effect. TMAO is able to fully compensate the prolonged lag phase induced by urea. This strongly matches the findings of a counteraction of TMAO and urea in protein folding and unfolding experiments. The data also reveal that the influence of these cosolvents is only on the aggregation kinetics without markedly changing the final IAPP fibrillar morphology, i.e., the solution structure and cosolvent composition essentially affect the kinetics of the fibrillation process only.

Elevated osmolytes in rainbow smelt: the effects of urea, glycerol and trimethylamine oxide on muscle contractile properties

“…Additional physiological functions that are impacted by elevated levels of osmolytes have recently been identified. For instance, elevated TMAO is linked to type-2 diabetes (Seeliger et al, 2013). Another osmolyte, urea, is elevated in humans under certain conditions; for instance, extreme endurance events such as ironman triathlons (Knechtle et al, 2010a,b).…”

Co-evolution of proteins and solutions: protein adaptation versus cytoprotective micromolecules and their roles in marine organisms

“…Stabilizing properties of cosolutes led to the term 'chemical chaperone', as a counterpart to the term 'molecular chaperone' for stress proteins such as heat-shock proteins (hsp); and led to proposals to use them to treat protein-folding diseases (Welch and Brown, 1996;Zhao et al, 2007;Gong et al, 2009;Jia et al, 2009;Seeliger et al, 2013) and to enhance protein stability in biochemical and pharmaceutical preparations (e.g. Marshall et al, 2012).…”

Synergistic Inhibition of Protein Fibrillation by Proline and Sorbitol: Biophysical Investigations

“…Osmolytes mainly include amino acids and their derivatives, polyols, sugars and methylamines. Compounds such as glycine, N-methylglycine, N,N-dimethylglycine, N,N,N-trimethylglycine, trimethyl-N-oxide, polyethylene glycols, sucrose, trehalose, glycerol and many others also fall under this category and have been found to increase stability in several proteins[15–19]. Likewise, many compounds such as glycerol, sorbitol, sucrose, glycine, proline, betaine, sarcosine and trimethyl-N-amine have been found to be effective against protein aggregation [17, 19].…”

“…Compounds such as glycine, N-methylglycine, N,N-dimethylglycine, N,N,N-trimethylglycine, trimethyl-N-oxide, polyethylene glycols, sucrose, trehalose, glycerol and many others also fall under this category and have been found to increase stability in several proteins[15–19]. Likewise, many compounds such as glycerol, sorbitol, sucrose, glycine, proline, betaine, sarcosine and trimethyl-N-amine have been found to be effective against protein aggregation [17, 19]. Considering the direct influence of chemical chaperones on proteins’ structure, stability, solubility and folding reactions [19, 20] it may be envisaged that they may modulate the tendency of the proteins to aggregate and also the nature of the aggregates that would be formed [21–24].…”

“…Likewise, many compounds such as glycerol, sorbitol, sucrose, glycine, proline, betaine, sarcosine and trimethyl-N-amine have been found to be effective against protein aggregation [17, 19]. Considering the direct influence of chemical chaperones on proteins’ structure, stability, solubility and folding reactions [19, 20] it may be envisaged that they may modulate the tendency of the proteins to aggregate and also the nature of the aggregates that would be formed [21–24]. …”