Multiple roles of heparin in the aggregation of p25α.
The 219-residue protein p25α stimulates the fibrillation of α-synuclein (αSN) in vitro and colocalizes with it in several α-synucleinopathies. Although p25α does not fibrillate by itself under native conditions in vitro, αSN-free p25α 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 p25α aggregation. Heparin, polyglutamate, arachidonic acid micelles, and RNA all induce p25α 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-p25α 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 p25α, 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 p25α to heparin. We conclude that the modest structural changes that p25α 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.
Interdisciplinary Nanoscience Research Center, Center for Insoluble Structures, Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10C, DK-8000 Aarhus C, Denmark.
Søren Bang
SB
Nielsen
Pernille
P
Yde
Lise
L
Giehm
Sabrina
S
Sundbye
Gunna
G
Christiansen
Joachim
J
Mathiesen
Mogens Høgh
MH
Jensen
Poul Henning
PH
Jensen
Daniel E
DE
Otzen
D000682:Amyloid / Q000737:chemistry / Q000378:metabolism; D016718:Arachidonic Acid / Q000378:metabolism; D006493:Heparin / Q000378:metabolism*; D006801:Humans; D046911:Macromolecular Substances / Q000378:metabolism* / Q000648:ultrastructure; D018625:Microscopy, Atomic Force; D008854:Microscopy, Electron; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000378:metabolism*; D011099:Polyglutamic Acid / Q000378:metabolism; D011489:Protein Denaturation; D055503:Protein Multimerization; D012313:RNA / Q000378:metabolism
D000682:Amyloid; D046911:Macromolecular Substances; D009419:Nerve Tissue Proteins; C118136:TPPP protein, human; D011099:Polyglutamic Acid; D016718:Arachidonic Acid; D012313:RNA; D006493:Heparin