Missense mutations (A30P and A53T) in alpha-synuclein and the overproduction of the wild-type protein cause familial forms of Parkinson's disease and dementia with Lewy bodies. Alpha-synuclein is the major component of the filamentous Lewy bodies and Lewy neurites that define these diseases at a neuropathological level. Recently, a third missense mutation (E46K) in alpha-synuclein was described in an inherited form of dementia with Lewy bodies. Here, we have investigated the functional effects of this novel mutation on phospholipid binding and filament assembly of alpha-synuclein. When compared to the wild-type protein, the E46K mutation caused a significantly increased ability of alpha-synuclein to bind to negatively charged liposomes, unlike the previously described mutations. The E46K mutation increased the rate of filament assembly to the same extent as the A53T mutation. Filaments formed from E46K alpha-synuclein often had a twisted morphology with a cross-over spacing of 43 nm. The observed effects on lipid binding and filament assembly may explain the pathogenic nature of the E46K mutation in alpha-synuclein.

Parkinson’s disease (PD) is characterized by intracellular, insoluble Lewy bodies composed of highly stable α-synuclein (α-syn) amyloid fibrils. α-synuclein is an intrinsically disordered protein that has the capacity to assemble to form β-sheet rich fibrils. Oxidiative stress and metal rich environments have been implicated in triggering assembly. Here, we have explored the composition of Lewy bodies in post-mortem tissue using electron microscopy and immunogold labeling and revealed dityrosine crosslinks in Lewy bodies in brain tissue from PD patients. In vitro, we show that dityrosine cross-links in α-syn are formed by covalent ortho-ortho coupling of two tyrosine residues under conditions of oxidative stress by fluorescence and confirmed using mass-spectrometry. A covalently cross-linked dimer isolated by SDS-PAGE and mass analysis showed that dityrosine dimer was formed via the coupling of Y39-Y39 to give a homo dimer peptide that may play a key role in formation of oligomeric and seeds for fibril formation. Atomic force microscopy analysis reveals that the covalent dityrosine contributes to the stabilization of α-syn assemblies. Thus, the presence of oxidative stress induced dityrosine could play an important role in assembly and toxicity of α-syn in PD.

Fibrillar inclusions are a characteristic feature of the neuropathology found in the a-synucleinopathies such as Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. Familial forms of asynucleinopathies have also been linked with missense mutations or gene multiplications that result in higher protein expression levels. In order to form these fibrils, the protein, a-synuclein (a-syn), must undergo a process of self-assembly in which its native state is converted from a disordered conformer into a b-sheet-dominated form. Here, we have developed a novel polypeptide property calculator to locate and quantify relative propensities for b-strand structure in the sequence of a-syn. The output of the algorithm, in the form of a simple x-y plot, was found to correlate very well with the location of the b-sheet core in a-syn fibrils. In particular, the plot features three peaks, the largest of which is completely absent for the nonfibrillogenic protein, b-syn. We also report similar significant correlations for the Alzheimer's diseaserelated proteins, Ab and tau. A substantial region of a-syn is also of converting from its disordered conformation into a long amphipathic a-helical protein. We have developed the aforementioned algorithm to locate and quantify the a-helical hydrophobic moment in the amino acid sequence of a-syn. As before, the output of the algorithm, in the form of a simple x-y plot, was found to correlate very well with the location of a-helical structure in membrane bilayer-associated a-syn.