title: Solution conditions determine the relative importance of nucleation and growth processes in α-synuclein aggregation.
abstract: The formation of amyloid fibrils by the intrinsically disordered protein α-synuclein is a hallmark of Parkinson disease. To characterize the microscopic steps in the mechanism of aggregation of this protein we have used in vitro aggregation assays in the presence of preformed seed fibrils to determine the molecular rate constant of fibril elongation under a range of different conditions. We show that α-synuclein amyloid fibrils grow by monomer and not oligomer addition and are subject to higher-order assembly processes that decrease their capacity to grow. We also find that at neutral pH under quiescent conditions homogeneous primary nucleation and secondary processes, such as fragmentation and surface-assisted nucleation, which can lead to proliferation of the total number of aggregates, are undetectable. At pH values below 6, however, the rate of secondary nucleation increases dramatically, leading to a completely different balance between the nucleation and growth of aggregates. Thus, at mildly acidic pH values, such as those, for example, that are present in some intracellular locations, including endosomes and lysosomes, multiplication of aggregates is much faster than at normal physiological pH values, largely as a consequence of much more rapid secondary nucleation. These findings provide new insights into possible mechanisms of α-synuclein aggregation and aggregate spreading in the context of Parkinson disease.
authors.affiliation: Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom; and.
authors.forename: Alexander K
authors.initials: AK
authors.lastname: Buell
authors.affiliation: Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom; and.
authors.forename: Céline
authors.initials: C
authors.lastname: Galvagnion
authors.affiliation: Departments of Physical Chemistry and.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Gaspar
authors.affiliation: Departments of Physical Chemistry and.
authors.forename: Emma
authors.initials: E
authors.lastname: Sparr
authors.affiliation: Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom; and.
authors.forename: Michele
authors.initials: M
authors.lastname: Vendruscolo
authors.affiliation: Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom; and.
authors.forename: Tuomas P J
authors.initials: TP
authors.lastname: Knowles
authors.affiliation: Biochemistry and Structural Biology, Lund University, SE221 00 Lund, Sweden.
authors.forename: Sara
authors.initials: S
authors.lastname: Linse
authors.affiliation: Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom; and cmd44@cam.ac.uk.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Dobson
mesh_terms: D000682:Amyloid / Q000096:biosynthesis*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D018625:Microscopy, Atomic Force; D010300:Parkinson Disease / Q000378:metabolism*; D055672:Static Electricity; D051844:alpha-Synuclein / Q000378:metabolism*
chemical_list: D000682:Amyloid; D051844:alpha-Synuclein
keywords: electrostatic interactions; kinetic analysis; neurodegenerative disease; prion-like behavior; seeding