Transition of Structurally Distinct Amyloids in the Degradation of Protein Materials

Amyloid materials are formed from the aggregation of single proteins, yet contain polymorphisms where bulk properties are defined by a composition of multiple fibril types. Though desirable as a sustainable material, little is known about how various fibril types survive at high temperatures or in nonpolar solvents due to their highly similar molecular and nanoscale features. Here, we demonstrate that in situ two-dimensional infrared spectroscopy (2DIR), when paired with nanoscale microscopy, can determine the transition temperature of amyloid subpopulations without the use of labels. We use this capability to shed light on the molecular transition mechanism for amyloid polymorphs found in bulk materials formed from model proteins β-Lactoglobulin (β-Lg) and lysozyme. Smaller, worm-like polymorphs are formed initially by both proteins but exhibit stability only up to 80-90 °C, leaving mostly mature fibrils upon further heating. While mature β-Lg fibrils survived all thermal conditions tested (>230 °C), lysozyme fibrils revert to a structured monomeric protein state at 100 °C that could once again form fibrils upon cooling the solution. Molecular mechanisms outlined by our combined techniques shed light on the liquid-solid phase behavior of bulk protein gels and provide new insight toward the development of sustainable biomaterials such as amyloids for practical uses.