Oligomeric assembly of native-like precursors precedes amyloid formation by beta-2 microglobulin.
The deposition of beta-2-microglobulin (beta2m) as amyloid fibers results in debilitating complications for renal failure patients who are treated by hemodialysis. In vitro, wild-type beta2m can be converted to amyloid under physiological conditions by exposure to biomedically relevant concentrations of Cu(2+). In this work, we have made comparative measurements of the structural and oligomeric changes in beta2m at time points preceding fibrillogenesis. Our results show Cu(2+) mediates the formation of a monomeric, activated state followed by the formation of a discrete dimeric intermediate. The dimeric intermediates then assemble into tetra- and hexameric forms which display little additional oligomerization on the time scales of their own formation (<1 h). Amyloid fiber formation progresses from these intermediate states but on much longer time scales (>1 week). Although Cu(2+) is necessary for the generation and stabilization of these intermediates, it is not required for the stability of mature amyloid fibers. This suggests that Cu(2+) acts as an initiating factor of amyloidosis by inducing oligomer formation. (1)H NMR and near-UV circular dichroism are used to establish that oligomeric intermediates are native-like in structure. The native-like structure and discrete oligomeric size of beta2m amyloid intermediates suggest that this protein forms fibrils by structural domain swapping.
Eakin
Catherine M
CM
Department of Molecular Biophysics and Biochemistry, Yale University, 260 Whitney Avenue, New Haven, Connecticut 06520-8114, USA.
Attenello
Frank J
FJ
Morgan
Charles J
CJ
Miranker
Andrew D
AD
D000682:Amyloid / Q000096:biosynthesis*; D001704:Biopolymers / Q000737:chemistry / Q000378:metabolism*; D002942:Circular Dichroism; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D001613:beta 2-Microglobulin / Q000737:chemistry / Q000378:metabolism*
D000682:Amyloid; D001704:Biopolymers; D001613:beta 2-Microglobulin