Self-Assembly of the Synthetic Polymer (Leu-Glu)<i>_n</i>:  An Amyloid-like Structure Formation

Abstract

Self-assembly of β-sheet domains resulting in the formation of pathogenic fibrillar protein aggregates (amyloids) is the causative factor in Alzheimer's, Huntington's, and Creutzfeldt−Jakob diseases. Even though different kinds of protein sequences are known to form toxic structures (amyloids), the underlying mechanism whereby protein aggregation leads to amyloid structure formation is yet to be explained clearly. In this investigation, we have shown that a simple polypeptide, poly(Leu-Glu), on aging in an aqueous solution undergoes structural transition from the soluble monomeric form to amyloid structured aggregates. Water-soluble poly(Leu-Glu) peptide slowly self-assembles into fibrillar structures as evidenced by Fourier transform infrared and circular dichroism spectroscopic methods and thioflavin T binding assay. The polypeptide underwent conformational change from a structure with a mixture of coil & turn to a macromolecular β-sheet conformation and formed amyloid-like fibrils. The fibrils were examined by Congo red staining and transmission electron microscopy. The results indicate that transition from a disordered to an ordered tertiary structure consists of both fundamental helical turns and β-sheet repeats. The comprehensive spectroscopic and microscopic studies suggest that synthetic poly(Leu-Glu) is capable of forming an amyloid-like structure.