The Effect of Osmolytes on Protein Fibrillation

Abstract

Osmolytes are small molecules that are exploited by cells as a protective system against stress conditions. They favour compact protein states which makes them stabilize globular proteins in vitro and promote folding. Conversely, this preference for compact states promotes aggregation of unstructured proteins. Here we combine a brief review of the effect of osmolytes on protein fibrillation with a report of the effect of osmolytes on the unstructured peptide hormone glucagon. Our results show that osmolytes either accelerate the fibrillation kinetics or leave them unaffected, with the exception of the osmolyte taurine. Furthermore, the osmolytes that affected the shape of the fibrillation time profile led to fibrils with different structure as revealed by CD. The structural changes induced by Pro, Ser and choline-O-sulfate could be due to specific osmolytes binding to the peptides, stabilizing an otherwise labile fibrillation intermediate.

Structural Transitions and Interactions in the Early Stages of Human Glucagon Amyloid Fibrillation

“…Quantitative determination of sequence-dependent protection from HDX shows that the N-terminal segment (residues 1-9) does not participate in the interactions involved in the early stages of fibrillation, because deuterium incorporation is relatively unchanged for this segment. In contrast, residues (22)(23)(24)(25)(26)(27)(28)(29) spanning the C-terminal segment show decreases in deuterium incorporation consistent with intermolecular association (Fig. 5).…”

“…5 B). Peptic fragments 1-6, 1-9, and 10-21 still showed~25%,~14%, and~10% deuterium uptake, respectively, after 1440 min, whereas deuterium incorporation for the C-terminus (residues [22][23][24][25][26][27][28][29] was <1% after only 480 min of fibrillation (Figs. 5 A and S4).…”

“…However, any changes to the amino acid sequence or structure of a small peptide such as glucagon may impact biological activity (14)(15)(16)(17)(18)(19), and so are not without risk. Attempts to stabilize glucagon using readily available formulation additives have generally been ineffective or limited in their ability to stabilize the native structure (20)(21)(22).…”

Biological Wonders of Osmolytes: The Need to Know More

“…For instance, several types of osmolytes induce aggregation/fibrillation in intrinsically disordered protein α-synuclein which is associated with Parkinson's disease [72][73][74]. Other intrinsically disordered proteins which undergo aggregation/fibrillation by some osmolytes include tau protein [75], the prion protein [76], Alzheimer's amyloid β-peptides [77,78] and glucagon hormone peptide [64].…”

“…Protein fibrillation is responsible for several amyloidogenic disorders including diseases such as Alzheimer's, Parkinson's, mad cow, diabetes type II, cystic fibroisis, and dialysis related amyloidosis [58,59]. Though there have been several studies describing the effects of osmolytes on fibrillation/aggregation of proteins [60][61][62][63][64][65][66], quantitative understanding in terms of energetics of interaction has only recently been addressed Page 3 of 5 [67,68]. Trehalose has been currently used for the treatment of Huntington's disease in transgenic animal mice [69].…”