Unique Effect of Cu(II) in the Metal-Induced Amyloid Formation of β-2-Microglobulin

Abstract

β-2-Microglobulin (β2m) forms amyloid fibrils in the joints of patients undergoing hemodialysis treatment as a result of kidney failure. In the presence of stoichiometric amounts of Cu(II), β2m self-associates into discrete oligomeric species, including dimers, tetramers, and hexamers, before ultimately forming amyloid fibrils that contain no copper. To improve our understanding of whether Cu(II) is unique in its ability to induce β2m amyloid formation and to delineate the coordinative interactions that allow Cu(II) to exert its effect, we have examined the binding of Ni(II) and Zn(II) to β2m and the resulting influence that these metals have on β2m aggregation. We find that, in contrast to Cu(II), Ni(II) does not induce the oligomerization or aggregation of β2m, while Zn(II) promotes oligomerization but not amyloid fibril formation. Using X-ray absorption spectroscopy and new mass spectrometry-related techniques, we find that different binding modes are responsible for the different effects of Ni(II) and Zn(II). By comparing the binding modes of Cu(II) with Ni(II), we find that Cu(II) binding to Asp59 and the backbone amide between the first two residues of β2m are important for allowing the formation of amyloid-competent oligomers, as Ni(II) appears not to bind these sites on the protein. The oligomers formed in the presence of Zn(II) are permitted by this metal’s ability to bridge two β2m units via His51. These oligomers, however, are not able to progress to form amyloid fibrils because Zn(II) does not induce the required structural changes near the N-terminus and His31.

An XAS investigation of the nickel site structure in the transcriptional regulator InrS

“…X-ray absorption spectroscopy (XAS) data were collected as previously described[8, 9] on beam line X3B at the National Synchrotron Light Source (NSLS), Brookhaven National Laboratories (Upton, NY), except for Ni(II)-H21L, which used beam line 7-3 at the Stanford Synchrotron Radiation Laboratory (SSRL). Data collected at NSLS used samples that were cooled to ~30 K using a He displex cryostat and were collected under ring conditions of 2.8 GeV and 120–300 mA, with a sagittally-focusing Si(111) double-crystal monochromator.…”

Zinc-Induced Polymerization of Killer-Cell Ig-like Receptor into Filaments Promotes Its Inhibitory Function at Cytotoxic Immunological Synapses

“…While Zn 2+ and Cu 2+ can promote amyloid fibrillation and deposition, such fibrils are resistant to metal chelation (Bush and Tanzi, 2002; Dong et al, 2014). In contrast, KIR2DL1 filaments were easily dissociated upon zinc chelation (Figure 1C, 1E, 1F).…”

“…This degree of selectivity is analogous to the formation of β2-microglobulin oligomers in the presence of Cu 2+ , which are reversible by chelation prior to their progression into irreversible β2-microglobulin amyloid fibrils (Calabrese et al, 2008). Zn 2+ , in contrast, induced β2-microglobulin polymerization into amorphous aggregates (Dong et al, 2014). …”

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

“…18 Zn(II) initiates the formation of β2m oligomers, yet the types of oligomers that are formed are different than when Cu(II) is present. Moreover, amorphous, rather than amyloid, aggregates are eventually formed, and these aggregates can be readily re-dissolved with sodium dodecyl sulfate (SDS), whereas the amyloid fibrils formed by Cu(II) cannot be re-dissolved by SDS.…”

“…These structural changes include the cis-trans isomerization of the His31-Pro32 amide bond, as revealed by X-ray crystallography, that causes a repacking of the hydrophobic core and the repositioning of Arg3 and Asp59 to enable the formation of dimer-stabilizing salt bridges. 18,29,33 …”