Conformational Properties Relevant to the Amyloidogenicity of β₂-Microglobulin Analyzed Using Pressure- and...

β₂-Microglobulin (β₂m) is associated with dialysis-related amyloidosis. In vitro experiments have shown that β₂m forms amyloid fibrils at acidic pHs in the presence of moderate concentrations of salt. Previous studies suggested that acid-denatured β₂m has a hydrophobic residual structure, and the exposure of the hydrophobic residues enhances the association with seeds or other β₂m monomers. However, the nature of the residual structure relevant to its amyloidogenicity remains to be investigated. To understand the structural properties of acid-denatured β₂m and the role of salt, we investigated pressure- and salt concentration-dependent conformational changes by nuclear magnetic resonance spectroscopy and other methods. Here, pressure was utilized to characterize the conformers existing in a conformational equilibrium at ambient pressure. The obtained pressure- and salt concentration-dependent chemical shift data were simultaneously subjected to principal component analysis to characterize individual conformational change events. Unexpectedly, the addition of salt induced an expansion of the β₂m molecule, which likely resulted from the exclusion of the N-terminal region from the hydrophobic cluster region. The dissected chemical shift patterns for the salt-induced conformational change and other experimental data indicated that this conformational change caused a rigidification in the intrinsic hydrophobic cluster, leading to the observed amyloidogenicity.