Increased β-Sheet Dynamics and D-E Loop Repositioning Are Necessary for Cu(II)-Induced Amyloid Formation by β-2-Microglobulin

beta-6-2-Microglobulin (beta 2m) forms amyloid fibrils in the joints of patients undergoing dialysis treatment as a result of kidney failure. One of the ways in which beta 2m "can be induced to form atnyloid fibrils in vitro is via incubation with stoichiometric amounts of Cu(II). To better understand the structural changes caused by Cu(II) binding that allow beta 2m to form amyloid fibrils, we compared the effect of Ni(II) and Zn(II) binding, which are two similarly sized divalent metal ions that do not induce beta 2m amyloid formation. Using hydrogen/deuterium exchange mass spectrometry (HDX/MS) and covalent labeling MS, we find that Ni(II) has little effect on beta 2m structure, despite binding in the same region of the protein as Cu(II). This observation indicates that subtle differences in the organization of residues around Cu(II)' cause distant changes that are necessary for oligomerization and eventual amyloid formation. One key difference that we find is that only Cu(II), not. Ni(II) or Zn(II), is able to cause the cis trans isomerization of Pro32 that is an important conformational switch that initiates fian amyloid formation. By comparing HDX/MS data from the three metal beta 2m complexes, we also discover that increased dynamics in the beta-sheet formed by the A, B, D, and E /3 strands of the protein and repositioning of residues in the D E loop are necessary aspects of beta 2m forming an amyloid-competent dimer. Altogether, our results, reveal new structural insights into the unique effect of Cu(II) in the metal-induced amyloid formation of beta 2m.