Kidney dialysis-associated amyloidosis: a molecular role for copper in fiber formation

In the US alone, more than 250,000 people have impaired renal function that necessitates treatment by dialysis. A debilitating complication of long-term treatment is the deposition of beta2-microglobulin (beta2m) as amyloid fibers within the joint space. However, the intrinsic propensity of isolated beta2m protein to initiate in vitro fiber formation is negligible under conditions matched to the neutral pH and ionic conditions of serum. Here, we present evidence for a novel interaction between beta2m and Cu(2+) at a concentration within institutionally recommended limits for this metal ion in dialysate solution. Mass spectrometry, using electrospray ionization from native conditions, demonstrates that the binding of Cu(2+) is specific over Ca(2+) or Zn(2+). Despite maintaining a native-like conformation upon Cu(2+) binding, the folded protein is unusually destabilized against thermal and urea denaturation. We further demonstrate that destabilization by Cu(2+) uniquely promotes de novo fiber formation at 37 degrees C and neutral pH. Since the incidence of amyloidosis is dramatically reduced upon elimination of copper from dialysis membranes, our results provide a molecular understanding for dialysis-associated amyloid formation by beta2m.