Fiber diffraction of synthetic alpha-synuclein filaments shows amyloid-like cross-beta conformation

Filamentous inclusions made of alpha-synuclein constitute the defining neur opathological characteristic of Parkinson's disease, dementia with Lewy bod ies, and multiple system atrophy. Rare familial cases of Parkinson's diseas e are associated with mutations A53T and A30P in alpha-synuclein. We report here the assembly properties and secondary structure characteristics of re combinant alpha-synuclein. Carboxy-terminally truncated human alpha-synucle in (1-87) and (1-120) showed the fastest rates of assembly, followed by hum an A53T alpha-synuclein, and rat and zebra finch alpha-synuclein. Wild-type human alpha-synuclein and the A30P mutant showed slower rates of assembly. Upon shaking, filaments formed within 48 h at 37 degrees C. The related pr oteins beta- and gamma-synuclein only assembled after several weeks of incu bation. Synthetic human alpha-synuclein filaments were decorated by an anti body directed against the carboxy-terminal 10 amino acids of alpha-synuclei n, as were filaments extracted from dementia with Lewy bodies and multiple system atrophy brains. Circular dichroism spectroscopy indicated that alpha -synuclein undergoes a conformational change from random coil to beta-sheet structure during assembly. X-ray diffraction and electron diffraction of t he alpha-synuclein assemblies showed a cross-beta conformation characterist ic of amyloid.