Formation of β‑Lactoglobulin Nanofibrils by Microwave Heating Gives a Peptide Composition Different from Conventional Heating

• Published in: Biomacromolecules Vol. 13; no. 9; pp. 2868 - 2880
• Main Authors: Hettiarachchi, Charith A, Melton, Laurence D, Gerrard, Juliet A, Loveday, Simon M
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 10.09.2012
• Subjects: Amino Acid Sequence; Amyloid - chemistry; Analytical, structural and metabolic biochemistry; Animals; Applied sciences; Biological and medical sciences; Cattle; Circular Dichroism; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Heating; Hydrogen-Ion Concentration; Hydrolysis; Hydrophobic and Hydrophilic Interactions; Lactoglobulins - chemistry; Mass Spectrometry; Microscopy, Atomic Force; Microwaves; Miscellaneous; Models, Molecular; Molecular Mimicry; Molecular Sequence Data; Nanofibers - chemistry; Nanofibers - radiation effects; Natural polymers; Physicochemistry of polymers; Protein Structure, Secondary - radiation effects; Proteins; Spectroscopy, Fourier Transform Infrared; Self assembly; Circular dichroism spectrum; β-Lactoglobulin; Structure modification; Chemical composition; Kinetics; Aqueous solution; Microwave heating; Experimental study; Secondary structure; Globular protein
• ISSN: 1525-7797; 1526-4602
• DOI: 10.1021/bm300896r

A novel procedure involving microwave heating (MH) at 80 °C can be used to induce self-assembly of β-lactoglobulin (β-lg) into amyloid-like nanofibrils at low pH. We examined the self-assembly induced by MH, and evaluated structural and compositional differences between MH fibrils and those formed by conventional heating (CH). MH significantly accelerated the self-assembly of β-lg, resulting in fully developed fibrils in ≤2 h. However, longer MH caused irreversible disintegration of fibrils. An increase in the fibril yield was observed during the storage of the 2 h MH sample, which gave a yield similar to that of 16 h CH sample. Fourier transform infrared (FTIR) and circular dichroism (CD) spectra suggested that the fibrils formed by the two methods do not show significant differences in their secondary structure components. However, they exhibited differences in surface hydrophobicity, and mass spectrometry showed that the MH fibrils contained larger peptides than CH fibrils, including intact β-lg monomers, providing evidence for a different composition between the MH and CH fibrils, in spite of no observed differences in their morphology. We suggest MH initially accelerates the self-assembly of β-lg due to its nonthermal effects on unfolding, nucleation, and subsequent stacking of β-sheets, rather than promoting partial hydrolysis. Thus, MH fibrils are composed of larger peptides, and the observed higher surface hydrophobicity for the MH fibrils was attributed to the parts of the larger peptides extending out of the core structure of the fibrils.