Conformational Properties Relevant to the Amyloidogenicity of β2-Microglobulin Analyzed Using Pressure- and Salt-Dependent Chemical Shift Data.

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.