Evidence for a Partially Folded Intermediate in α-Synuclein Fibril Formation

Abstract

Intracellular proteinaceous aggregates (Lewy bodiesand Lewy neurites) of ␣-synuclein are hallmarks of neurodegenerative diseases such as Parkinson's disease, dementia with Lewy bodies, and multiple systemic atrophy. However, the molecular mechanisms underlying ␣-synuclein aggregation into such filamentous inclusions remain unknown. An intriguing aspect of this problem is that ␣-synuclein is a natively unfolded protein, with little or no ordered structure under physiological conditions. This raises the question of how an essentially disordered protein is transformed into highly organized fibrils. In the search for an answer to this question, we have investigated the effects of pH and temperature on the structural properties and fibrillation kinetics of human recombinant ␣-synuclein. Either a decrease in pH or an increase in temperature transformed ␣-synuclein into a partially folded conformation. The presence of this intermediate is strongly correlated with the enhanced formation of ␣-synuclein fibrils. We propose a model for the fibrillation of ␣-synuclein in which the first step is the conformational transformation of the natively unfolded protein into the aggregation-competent partially folded intermediate.

Temperature‐dependent structural changes in intrinsically disordered proteins: Formation of α‒helices or loss of polyproline II?

“…[20][21][22][23][24][25][26] This suggests that many IDPs undergo a structural change with increasing temperature. Different models have been put forward to explain this observation; however, the data do not decisively determine which explanation is correct, mainly because of the lack of atomic resolution information.…”

“…Most of these studies have identified structural changes upon heating that were interpreted mostly as formation of a-helices and to a minor extent to a loss of PPII structure. [20][21][22][23][24][25][26] The interpretation of the changes observed by CD spectroscopy is ambiguous. This is caused by the low resolution of this technique and the fact that structural changes in different segments may have spectroscopic contributions that cancel each other's signal.…”

Probing the origins, diagnosis and treatment of amyloid diseases using antibodies

“…In such species, the peptide or protein involved exposes at least part of its main chain and hydrophobic residues to the solvent under conditions in which intermolecular interactions can take place. In the case Textbox 1 of globular proteins, the formation of amyloidogenic intermediates involves the disruption of the native structure to a greater or lesser extent [18][19][20]; in natively unfolded proteins or unstructured peptides, this step may involve the formation of partially folded species with a high propensity to aggregate [21,22]. The second step is the self-association of the Fig.…”

Charge neutralization and collapse of the C‐terminal tail of alpha‐synuclein at low pH

“…When isolated in dilute solution at neutral pH, the protein shows a primarily disordered conformation without a well defined secondary or tertiary structure, 29 although both nascent secondary structure preferences 30 and transient tertiary interactions 31,32 are detectable. At Low pH, however, aS has been reported to adopt a more compact conformation with altered secondary structure content, 33 and the formation of this low pH intermediate conformation is maximal at pH 3.0. 33,34 At the same time, low pH accelerates aS fibril formation, indicating that the induced conformational changes favor fibril formation.…”

“…At Low pH, however, aS has been reported to adopt a more compact conformation with altered secondary structure content, 33 and the formation of this low pH intermediate conformation is maximal at pH 3.0. 33,34 At the same time, low pH accelerates aS fibril formation, indicating that the induced conformational changes favor fibril formation. Here we present a detailed study of the conformation of aS at pH 3.0, using NMR secondary chemical shifts, paramagnetic relaxation enhancement, and residual dipolar couplings.…”