The role of protein hydrophobicity in conformation change and self-assembly into large amyloid fibers.

It has been found that a short hydrophobic "template" peptide and a larger α-helical "adder" protein cooperatively self-assemble into micrometer sized amyloid fibers. Here, a common template of trypsin hydrolyzed gliadin is combined with six adder proteins (α-casein, α-lactalbumin, amylase, hemoglobin, insulin, and myoglobin) to determine what properties of the adder protein drive amyloid self-assembly. Utilizing Fourier Transform-Infrared (FT-IR) spectroscopy, the Amide I absorbance reveals that the observed decrease in α-helix with time is approximately equal to the increase in high strand density β-sheet, which is indicative of amyloid formation. The results show that the hydrophobic moment is a good predictor of conformation change but the fraction of aliphatic amino acids within the α-helices is a better predictor. Upon drying, the protein mixtures form large amyloid fibers. The fiber twist is dependent on the aliphatic index and molecular weight of the adder protein. Here we demonstrate that it is possible to predict the propensity of an adder protein to unfold into an amyloid structure and to predict the fiber morphology, both from adder protein molecular features, which can be applied to the pragmatic engineering of large amyloid fibers.