Abstract
The intrinsically disordered protein α-synuclein (aSN) is, in its fibrillated state, the main component of Lewy bodies—hallmarks of Parkinson’s disease. Additional Lewy body components include glycosaminoglycans, including heparan sulfate proteoglycans. In humans, heparan sulfate has, in an age-dependent manner, shown increased levels of sulfation. Heparin, a highly sulfated glycosaminoglycan, is a relevant mimic for mature heparan sulfate and has been shown to influence aSN fibrillation. Here, we decompose the underlying properties of the interaction between heparin and aSN and the effect of heparin on fibrillation. Via the isolation of the first 61 residues of aSN, which lacked intrinsic fibrillation propensity, fibrillation could be induced by heparin, and access to the initial steps in fibrillation was possible. Here, structural changes with shifts from disorder via type I β-turns to β-sheets were revealed, correlating with an increase in the aSN1–61/heparin molar ratio. Fluorescence microscopy revealed that heparin and aSN1–61 co-exist in the final fibrils. We conclude that heparin can induce the fibrillation of aSN1–61, through binding to the N-terminal with an affinity that is higher in the truncated form of aSN. It does so by specifically modulating the structure of aSN via the formation of type I β-turn structures likely critical for triggering aSN fibrillation.
Highlights
The intrinsically disordered protein (IDP) α-synuclein [1] locates predominantly in the presynaptic termini in neurons, with a cytosolic concentration of 30–60 μM [2]
The 1H,15N-HSQC spectra of Abstract: The intrinsically disordered protein α-synuclein (aSN) and aSN1–61 were compared (Figure 1E), revealing that the vast majority of peaks of aSN1–61 overlaid those of full-length aSN
As we observed that heparin had different effects on the fibrillation of aSN1–61 depending on the molar ratio, we investigated the behavior of heparin alone in different buffers using Small Angle X-ray Scattering (SAXS)
Summary
The intrinsically disordered protein (IDP) α-synuclein (aSN) [1] locates predominantly in the presynaptic termini in neurons, with a cytosolic concentration of 30–60 μM [2]. The N-terminal region has been shown to play an important role in interactions with membranes and vesicles, both in vitro [7] and in vivo [8] In this region and the NAC region, aSN has a total of six evolutionary conserved K[T/A]K[E/Q][G/Q]V-motifs, which are believed to be important for its membrane interaction [6]. The cross-β core of aSN fibrils is formed by the NAC region, but recent high-resolution structures obtained by cryo-electron microscopy (EM) have shown that part of the N-terminal partakes in the fibril β-structure [12]. While previous studies suggested the N-terminal as inhibitory for fibrillation [15], recent studies have shown that N-terminal fragments, e.g., 15–65, can self-aggregate and, the structural nature of these aggregates was not fully determined, accelerate aggregation of full-length aSN [16]
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