Multiple Roles of Heparin in the Aggregation of p25¦Á
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- 作者：S?ren Bang Nielsen ; Pernille Yde ; Lise Giehm ; Sabrina Sundbye ; Gunna Christiansen ; Joachim Mathiesen ; Mogens H?gh Jensen ; Poul Henning Jensen ; Daniel E. Otzen
- 关键词：¦ÁSN ; ¦Á-synuclein ; PD ; Parkinson's disease ; PDB ; Protein Data Bank ; GAG ; glycosaminoglycan ; ThT ; thioflavin T ; HW ; high molecular weight ; AFM ; atomic force microscopy ; PBS ; phosphate-buffered saline ; CAC ; critical aggregation concentration ; DP ; degree of
- 刊名：Journal of Molecular Biology
- 出版年：2012
- 出版时间：24 August, 2012
- 年：2012
- 卷：421
- 期：4-5
- 页码：601-615
- 全文大小：1707 K
文摘
The 219-residue protein p25¦Á stimulates the fibrillation of ¦Á-synuclein (¦ÁSN) in vitro and colocalizes with it in several ¦Á-synucleinopathies. Although p25¦Á does not fibrillate by itself under native conditions in vitro, ¦ÁSN-free p25¦Á aggregates have also been observed in vivo in, for example, multiple system atrophy. To investigate which environmental conditions might trigger this aggregation, we investigated the effect of polyanionic biomolecules on p25¦Á aggregation. Heparin, polyglutamate, arachidonic acid micelles, and RNA all induce p25¦Á aggregation. More detailed studies using heparin as template for aggregation reveal that a minimum of 10-14 heparin monosaccharide units per heparin polymer are required. Bona fide fibrils are only formed at intermediate heparin concentrations, possibly because an excess of heparin binding sites blocks the inter-p25¦Á contacts required for amyloid formation. Other polyanions also show an optimum for amyloid formation. Aggregation involves only modest structural changes according to both spectroscopic and proteolytic experiments. The aggregates do not seed aggregation of heparin-free p25¦Á, suggesting that heparin is required in stoichiometric amounts to form organized structures. We are able to reproduce these observations in a model involving two levels of binding of p25¦Á to heparin. We conclude that the modest structural changes that p25¦Á undergoes can promote weak intermolecular contacts and that polyanions such as heparin play a central role in stabilizing these aggregates but in multiple ways, leading to different types of aggregates. This highlights the role of non-protein components in promoting protein aggregation in vivo.