American Chemical Society
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A Systematic Study of the Effect of Physiological Factors on β2-Microglobulin Amyloid Formation at Neutral pH

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journal contribution
posted on 2006-02-21, 00:00 authored by Sarah L. Myers, Susan Jones, Thomas R. Jahn, Isobel J. Morten, Glenys A. Tennent, Eric W. Hewitt, Sheena E. Radford
β2-microglobulin (β2m) forms amyloid fibrils that deposit in the musculo-skeletal system in patients undergoing long-term hemodialysis. How β2m self-assembles in vivo is not understood, since the monomeric wild-type protein is incapable of forming fibrils in isolation in vitro at neutral pH, while elongation of fibril-seeds made from recombinant protein has only been achieved at low pH or at neutral pH in the presence of detergents or cosolvents. Here we describe a systematic study of the effect of 11 physiologically relevant factors on β2m fibrillogenesis at pH 7.0 without denaturants. By comparing the results obtained for the wild-type protein with those of two variants (ΔN6 and V37A), the role of protein stability in fibrillogenesis is explored. We show that ΔN6 forms low yields of amyloid-like fibrils at pH 7.0 in the absence of seeds, suggesting that this species could initiate fibrillogenesis in vivo. By contrast, high yields of amyloid-like fibrils are observed for all proteins when assembly is seeded with fibril-seeds formed from recombinant protein at pH 2.5 stabilized by the addition of heparin, serum amyloid P component (SAP), apolipoprotein E (apoE), uremic serum, or synovial fluid. The results suggest that the conditions within the synovium facilitate fibrillogenesis of β2m and show that different physiological factors may act synergistically to promote fibril formation. By comparing the behavior of wild-type β2m with that of ΔN6 and V37A, we show that the physiologically relevant factors enhance fibrillogenesis by stabilizing fibril-seeds, thereby allowing fibril extension by rare assembly competent species formed by local unfolding of native monomers.