On the role of peptide hydrolysis for fibrillation kinetics and amyloid fibril morphology.

Xinchen Ye,Christofer Lendel,Maud Langton,Mikael S Hedenqvist

doi:10.1039/c7ra10981d

Abstract

Self-assembly of proteins into amyloid-like nanofibrils is not only a key event in several diseases, but such fibrils are also associated with intriguing biological function and constitute promising components for new biobased materials. The bovine whey protein β-lactoglobulin has emerged as an important model protein for the development of such materials. We here report that peptide hydrolysis is the rate-determining step for fibrillation of β-lactoglobulin in whey protein isolate. We also explore the observation that β-lactoglobulin nanofibrils of distinct morphologies are obtained by simply changing the initial protein concentration. We find that the morphological switch is related to different nucleation mechanisms and that the two classes of nanofibrils are associated with variations of the peptide building blocks. Based on the results, we propose that the balance between protein concentration and the hydrolysis rate determines the structure of the formed nanofibrils.

Highlights

The self-assembly of proteins into highly ordered, b-sheet rich nano brils, so-called amyloid brils, has developed into a major area of research during the last decades
The absence of a distinct lag phase can be explained by the high temperature and high protein concentrations and similar features have been reported by others.[18]
The fact that a double logarithmic plot of the measured t1/2 versus initial whey protein isolate (WPI) concentration (ESI Fig. S3†) does not follow any of the standard models for brillation suggests that the measured kinetics might re ect another process than the PNF assembly. To explore this further we applied a simpli ed approach where the initial reaction rates were estimated and we found a linear relationship between the initial rates and the WPI concentration (Fig. 1B)

Summary

Introduction

The self-assembly of proteins into highly ordered, b-sheet rich nano brils, so-called amyloid brils, has developed into a major area of research during the last decades. In this experiment the curved brils display higher emission intensity than the straight brils, which supports the conclusion that there are fundamental structural differences between the two morphological classes of PNFs. Taken together, our AFM data con rm a morphological switch between initial WPI concentrations of 40 and 60 g lÀ1 and biophysical characterization of the brils shows that distinct structural features are associated with each of the morphologies both can still be classi ed as amyloidlike.

Results

Conclusion