UBC Theses and Dissertations
Morphology, formation kinetics and core composition of pea and soy 7S and 11S globulin amyloid fibrils Zhang, Yuran
Legume seed storage proteins can be induced to form amyloid fibrils by heating at low pH, which could improve protein functionality for use in food and materials applications. However, amyloidogenic regions of legume proteins are largely unknown. In this study, crude protein extracts and the major seed storage proteins, 7S and 11S globulins from pea and soy were enriched and induced to form fibrils at pH 2, 80°C. The hydrolysis, fibrillation kinetics and fibril morphology were characterized by gel electrophoresis, Thioflavin-T (ThT) fluorescence assay and transmission electron microscopy (TEM). The amyloidogenic core regions of pea and soy 7S and 11S globulins were identified by liquid chromatography with tandem mass spectrometry (LC-MS/MS). It was found that all samples were further hydrolyzed and fragmented into shorter fibrils during extended heating (30 – 78 h). 7S globulins from either pea or soy displayed no lag phase whereas 11S globulins and crude extracts exhibited a similar lag time of around 8 h. Pea and soy protein fibrils demonstrated morphological differences where most pea protein fibrils were straight and soy protein fibrils were rather worm-like. Over 100 unique peptides were detected from the fibril core of pea 7S globulin, and over 50 unique peptides found in pea 11S globulin, soy 7S and 11S globulin fibril core, most of which could be mapped on several conserved fibril core regions. Amyloidogenic regions were restricted mainly to the homologous core region of 7S globulins and the basic subunit of 11S globulins. Overall, pea and soy 7S and 11S globulins are rich in amyloidogenic regions. This study further informs our understanding of legume protein fibrillation mechanism and engineering food protein fibrils with specific structures and functionality.
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