Probing a salt-induced conformational switch in β₂-microglobulin under low pH conditions

Self-assembly of proteins and peptides into amyloid fibrils is an active field of research due to its connection with debilitating human ailments such as Parkinson's disease, dialysis-related amyloidosis (DRA), and type II diabetes. In most disease conditions, amyloid formation proceeds via distinct on-pathway conformers such as oligomers and protofibrils. However, the detailed mechanism by which monomers transform into different species and contribute to disease progression remains an area of intense research. Isolating and characterizing distinct conformers are pertinent to understanding disease initiation and progression. One such ailment is DRA, where an amyloidogenic protein, β₂-microglobulin (β₂m), undergoes a profound conformational switch to adopt an amyloid fold. β₂m amyloids accumulate in tissues such as joints and kidneys, causing tissue damage and dysfunction. Soluble β₂m oligomers are considered more toxic than amyloids due to impaired cellular processes, resulting in cell death. In the present study, we have identified and characterized three stages of β₂m aggregation, namely, oligomers, protofibrils, and fibrils, while varying salt concentrations and agitation under low pH conditions. Our kinetic results indicate that β₂m oligomers and protofibrils follow a nucleation-independent pathway, whereas amyloids are formed through the classical nucleation process. Further, we implemented microscopic techniques and biochemical assays to verify the formation and stability of distinct conformers. We believe these findings provide insights into the process of amyloid formation, which may help us to understand the initiation of the disease at an early stage.