α-Synuclein Interacts with Glucocerebrosidase Providing a Molecular Link between Parkinson and Gaucher Diseases

Abstract

The presynaptic protein ␣-synuclein (␣-syn), particularly in its amyloid form, is widely recognized for its involvement in Parkinson disease (PD). Recent genetic studies reveal that mutations in the gene GBA are the most widespread genetic risk factor for parkinsonism identified to date. GBA encodes for glucocerebrosidase (GCase), the enzyme deficient in the lysosomal storage disorder, Gaucher disease (GD). In this work, we investigated the possibility of a physical linkage between ␣-syn and GCase, examining both wild type and the GD-related N370S mutant enzyme. Using fluorescence and nuclear magnetic resonance spectroscopy, we determined that ␣-syn and GCase interact selectively under lysosomal solution conditions (pH 5.5) and mapped the interaction site to the ␣-syn C-terminal residues, 118 -137. This ␣-syn-GCase complex does not form at pH 7.4 and is stabilized by electrostatics, with dissociation constants ranging from 1.2 to 22 M in the presence of 25 to 100 mM NaCl. Intriguingly, the N370S mutant form of GCase has a reduced affinity for ␣-syn, as does the inhibitor conduritol-␤-epoxidebound enzyme. Immunoprecipitation and immunofluorescence studies verified this interaction in human tissue and neuronal cell culture, respectively. Although our data do not preclude protein-protein interactions in other cellular milieux, we suggest that the ␣-syn-GCase association is favored in the lysosome, and that this noncovalent interaction provides the groundwork to explore molecular mechanisms linking PD with mutant GBA alleles.

α-Synuclein interacts with the switch region of Rab8a in a Ser129 phosphorylation-dependent manner

“…In addition, we found that mimicking αS phosphorylation increased the number of inclusions per cell. NMR spectroscopy suggests that the enhanced aggregation is due to a direct binding of Rab8a to the C-terminus of αS that has been implicated in interactions with a variety of protein partners (Burre et al, 2010;De Genst et al, 2010;Jensen et al, 1999Jensen et al, , 2000Kawamata et al, 2001;Kim et al, 2002;Yap et al, 2011). Thus, our study provides a link between physiological αS interactions and pathogenic aggregation.…”

Intracellular metabolite β-glucosylceramide is an endogenous Mincle ligand possessing immunostimulatory activity

“…In addition to Gaucher disease, GBA1 mutation is genetically correlated with Parkinson's disease (72). It has been hypothesized that this results from the ability of β-GlcCer to promote neurotoxic amyloid formation (73,74). As we have now identified β-GlcCer as a Mincle ligand, the role of Mincle in these processes presents an intriguing issue to be addressed for the understanding of this severe progressive disease.…”

Glucocerebrosidase mutations and the pathogenesis of Parkinson disease

“…The interaction site has been mapped to the C-terminus of SNCA. It has also been suggested that the binding between the WT GBA and SNCA, under lysosomal conditions, could have a beneficial effect by either promoting SNCA degradation by the lysosome and/or preventing aggregation (Yap et al, 2011). The authors propose another selfperpetuating model.…”

“…The suggested beneficial interaction between SNCA and WT GBA proposed to occur under lysosomal conditions (Yap et al, 2011) may suggest that techniques to increase GCase activity and improve its delivery to the lysosome could promote degradation through the autophagy pathway and reduce SNCA concentrations.…”