Journal
BIOPHYSICAL JOURNAL
Volume 108, Issue 8, Pages 2038-2047Publisher
CELL PRESS
DOI: 10.1016/j.bpj.2015.03.010
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Funding
- National Institutes of Health [GM096039]
- National Science Foundation [EPS-1004094]
- Branfman Family Foundation [GM098859]
- Office Of The Director
- EPSCoR [1004094] Funding Source: National Science Foundation
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The aggregation of alpha-synuclein (alpha-Syn) is linked to Parkinson's disease. The mechanism of early aggregation steps and the effect of pathogenic single-point mutations remain elusive. We report here a single-molecule fluorescence study of alpha-Syn dimerization and the effect of mutations. Specific interactions between tethered fluorophore-free alpha-Syn monomers on a substrate and fluorophore-labeled monomers diffusing freely in solution were observed using total internal reflection fluorescence microscopy. The results showed that wild-type (WT) alpha-Syn dimers adopt two types of dimers. The lifetimes of type 1 and type 2 dimers were determined to be 197 +/- 3 ms and 3334 +/- 145 ms, respectively. All three of the mutations used, A30P, E46K, and A53T, increased the lifetime of type 1 dimer and enhanced the relative population of type 2 dimer, with type 1 dimer constituting the major fraction. The kinetic stability of type 1 dimers (expressed in terms of lifetime) followed the order A30P (693 +/- 14 ms) > E46K (292 +/- 5 ms) > A53T (226 +/- 6 ms) > WT (197 +/- 3 ms). Type 2 dimers, which are more stable, had lifetimes in the range of several seconds. The strongest effect, observed for the A30P mutant, resulted in a lifetime 3.5 times higher than observed for the WT type 1 dimer. This mutation also doubled the relative fraction of type 2 dimer. These data show that single-point mutations promote dimerization, and they suggest that the structural heterogeneity of alpha-Syn dimers could lead to different aggregation pathways.
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