α-Synuclein is causative for autosomal dominant familial Parkinson disease and 
dementia with Lewy bodies, and the phosphorylation of α-synuclein at residue 
Ser-129 is a key posttranslational modification detected in Parkinson 
disease/dementia with Lewy bodies lesions. However, the role of Ser-129 
phosphorylation on the pathogenesis of Parkinson disease/dementia with Lewy 
bodies remains unclear. Here we investigated the neurotoxicity of 
Ser-129-substituted α-synuclein in the transgenic Caenorhabditis elegans (Tg 
worm) model of synucleinopathy. Tg worms pan-neuronally overexpressing 
nonphosphorylatable (S129A) α-synuclein showed severe defects including motor 
dysfunction, growth retardation, and synaptic abnormalities. In contrast, Tg 
worms expressing phosphorylation mimic (S129D) α-synuclein exhibited nearly 
normal phenotypes. Biochemical fractionation revealed that the level of 
membrane-bound α-synuclein was significantly increased in S129A-α-synuclein Tg 
worms, whereas S129D- as well as A30P-α-synuclein displayed lower membrane 
binding properties. Furthermore, A30P/S129A double mutant α-synuclein did not 
cause neuronal dysfunction and displayed low membrane binding property. In human 
neuroblastoma SH-SY5Y cells, localization of S129A-α-synuclein to membranes was 
significantly increased. Finally, gene expression profiling of S129A-Tg worms 
revealed a dramatic up-regulation of Daf-16/FOXO pathway genes, which likely act 
against the dysfunction caused by S129A-α-synuclein. These results imply a role 
of Ser-129 phosphorylation of α-synuclein in the attenuation of 
α-synuclein-induced neuronal dysfunction and downstream stress response by 
lowering the membrane binding property.