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

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 b-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 b-lactoglobulin in whey protein isolate. We also explore the observation that blactoglobulin 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.

Structural basis for the formation of soy protein nanofibrils

“…AFM images of the samples showed that the majority of the PNFs are rather short (typically between 0.1 and 0.5 mm) and highly curved (Fig. 2), similar to brils reported for the whey protein b-lactoglobulin under certain conditions 8,36,37 as well as other proteins. 13,34,38,39 However, a few longer (>1 mm) and more straight brils could also be observed.…”

“…More likely, it is related to the length and the physicochemical properties of the peptide segments as suggested for whey PNFs in our previous work. 8…”

“…associated with Alzheimer's or Parkinson's diseases) 1 but today the eld also covers natural functional amyloid, 2,3 engineered nanomaterials 4 and food science. 5 A variety of different protein sources have been explored for the latter two applications, such as whey, [6][7][8] egg, 9 sh waste 10 and various legumes. [11][12][13][14][15][16] Depending on protein source and brillation conditions, variations in the nanoscale morphology of the brils are commonly observed, which have substantial impact on their nanomechanical properties 17 as well as the properties of macroscale materials made from the PNFs.…”

“…11,13,16,19,[30][31][32] The fact that globular proteins are denatured likely contributes to the brillation-promoting effect at these conditions but it has also became evident that acid-induced hydrolysis of the peptide backbone can play a crucial role. 8,13,19,33,34 The role of hydrolysis can be understood in the light of that the core structures of PNFs only consist of parts of the full-length protein. Hence, large parts of the protein chain are not critical for forming the amyloid structure; rather it will in many cases lead to structural frustrations and reduce the thermodynamic stability of the PNF state.…”

“…A recent study from our lab also suggests that the PNF morphology, and thereby also the nanomechanical properties, can be determined by the hydrolysis process. 8 In the present study we explored the PNF-forming peptide segments in soy proteins with the aim to better understand how SPI, and potentially other plant proteins, can be used for production of PNFs with dened morphology for nanomaterial applications.…”