Neurodegeneration in Parkinson's disease is correlated with the occurrence of Lewy bodies, intracellular inclusions containing aggregates of the intrinsically disordered protein (IDP) α-Synuclein 1 . The aggregation propensity of α-Synuclein in cells is modulated by specific factors including posttranslational modifications 2,3 , Abelson-kinase-mediated phosphorylation 4,5 and interactions with intracellular machineries such as molecular chaperones, although the underlying mechanisms are unclear [6][7][8] . Here, we systematically characterize the interaction of molecular chaperones with α-Synuclein in vitro as well as in cells at the atomic level. We find that six vastly different molecular chaperones commonly recognize a canonical motif in α-Synuclein, consisting Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:http://www.nature.com/authors/editorial_policies/license.html#terms *

Quantitative kinetic analysis is critical for understanding amyloid mechanisms. Here we demonstrate the application of generic Finke-Watzky (F-W) two-step nucleation-autocatalytic growth model to the concentration-dependent amyloid kinetics of proinflammatory α-helical S100A9 protein at pH 7.4 and at 37 and 42 °C. The model is based on two pseudoelementary reaction steps applied without further analytical constraints, and its treatment of S100A9 amyloid self-assembly demonstrates that initial misfolding and β-sheet formation, defined as "nucleation" step, spontaneously takes place within individual S100A9 molecules at higher rate than the subsequent fibrillar growth. The latter, described as an autocatalytic process, will proceed if misfolded amyloid-prone S100A9 is populated on a macroscopic time scale. Short lengths of S100A9 fibrils are consistent with the F-W model. The analysis of fibrillar length distribution by the Beker-Döring model demonstrates independently that such distribution is solely determined by slow fibril growth and there is no fragmentation or secondary pathways decreasing fibrillar length.

Alterations in copper ion homeostasis appear coupled to neurodegenerative disorders, but mechanisms are unknown. The cytoplasmic copper chaperone Atox1 was recently found to inhibit amyloid formation in vitro of α-synuclein, the amyloidogenic protein in Parkinson’s disease. As α-synuclein may have copper-dependent functions, and free copper ions promote α-synuclein amyloid formation, it is important to characterize the Atox1 interaction with α-synuclein on a molecular level. Here we applied solution-state nuclear magnetic resonance spectroscopy, with isotopically labeled α-synuclein and Atox1, to define interaction regions in both proteins. The α-synuclein interaction interface includes the whole N-terminal part up to Gln24; in Atox1, residues around the copper-binding cysteines (positions 11–16) are mostly perturbed, but additional effects are also found for residues elsewhere in both proteins. Because α-synuclein is N-terminally acetylated in vivo, we established that Atox1 also inhibits amyloid formation of this variant in vitro, and proximity ligation in human cell lines demonstrated α-synuclein-Atox1 interactions in situ. Thus, this interaction may provide the direct link between copper homeostasis and amyloid formation in vivo.

An interdomain lock modulates the functionality of the bacterial periplasmic protease DegP via distinct oligomeric states.