A Lysozyme Concentration, pH, and Time-Dependent Isothermal Transformation Diagram Reveals Fibrous Amyloid and Non-Fibrous, Amorphous Aggregate Species

Deposition of aggregated protein is associated with many human diseases. The mechanism by which protein aggregate species cause cellular death remains unclear. A profile revealing protein aggregation products under a diverse set of conditions allows the search of novel aggregate products and potential pathogens. To achieve this end, an isothermal transformation diagram (ITD) of lysozyme aggregation was constructed. AFM, TEM, and Thioflavin T binding assays were used to analyze the aggregate species synthesized under a broad range of pH values, protein concentrations, and incubation times. Four states were found: 1) soluble protein species; 2) insoluble amyloid fibers; 3) insoluble amorphous aggregates; and 4) protein hydrogels. The hydrogel-a rises from aggregated amyloid fibers. This work is part of an effort to construct an array of ITDs reporting aggregation properties of many disease relevant proteins, including amyloid beta, tau, α-synuclein, and others involved in protein aggregation diseases. In addition, we propose hydrogel cyto toxicity as a potential novel mechanism in the pathogenesis of amyloid diseases.