Abstract
Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a multifunctional enzyme that has been associated with neurodegenerative diseases. GAPDH colocalizes with α-synuclein in amyloid aggregates in post-mortem tissue of patients with sporadic Parkinson disease and promotes the formation of Lewy body-like inclusions in cell culture. In a previous work, we showed that glycosaminoglycan-induced GAPDH prefibrillar species accelerate the conversion of α-synuclein to fibrils. However, it remains to be determined whether the interplay among glycosaminoglycans, GAPDH, and α-synuclein has a role in pathological states. Here, we demonstrate that the toxic effect exerted by α-synuclein oligomers in dopaminergic cell culture is abolished in the presence of GAPDH prefibrillar species. Structural analysis of prefibrillar GAPDH performed by small angle x-ray scattering showed a particle compatible with a protofibril. This protofibril is shaped as a cylinder 22 nm long and a cross-section diameter of 12 nm. Using biocomputational techniques, we obtained the first all-atom model of the GAPDH protofibril, which was validated by cross-linking coupled to mass spectrometry experiments. Because GAPDH can be secreted outside the cell where glycosaminoglycans are present, it seems plausible that GAPDH protofibrils could be assembled in the extracellular space kidnapping α-synuclein toxic oligomers. Thus, the role of GAPDH protofibrils in neuronal proteostasis must be considered. The data reported here could open alternative ways in the development of therapeutic strategies against synucleinopathies like Parkinson disease.
Highlights
Glycosaminoglycan-induced Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) prefibrillar species accelerates ␣-synuclein aggregation, its role in toxicity remains unclear
For ␣-SNoli ϩ GAPDH, ␣-SNoli was preincubated for 1 h at 37 °C with GAPDH (50 M). ␣-SNoli ϩ HI-GAPDHESS corresponds to ␣-SNoli preincubated for 1 h at 37 °C with HI-GAPDHESS
We have analyzed the most probable arrangement of GAPDH subunits within the protofibril considering the following constraints obtained from the small angle x-ray scattering (SAXS) data analysis: (i) it has a cylindrical shape, a diameter, and long axis lengths of 11.8 and 21.5 nm respectively; (ii) the number of subunits to be fitted into the cylinder (Nagg) is 35 Ϯ 2; (iii) the subunits maintain a native-like fold as observed on FTIR spectra recorded during the early stages of heparin- induced aggregation [27]; (iv) a native-like dimer can be used as the building block because this species is present in the early stages of the fibrillation process (Fig. 2)
Summary
Glycosaminoglycan-induced GAPDH prefibrillar species accelerates ␣-synuclein aggregation, its role in toxicity remains unclear. GAPDH colocalizes with ␣-synuclein in amyloid aggregates in post-mortem tissue of patients with sporadic Parkinson disease and promotes the formation of Lewy body-like inclusions in cell culture. GAPDH colocalizes with ␣-SN in amyloid aggregates in post-mortem tissue of patients with sporadic Parkinson disease and promotes the formation of Lewy body-like inclusions in cell culture. Upon secretion in the extracellular space, GAPDH might interact with GAGs leading to the formation of GAPDH protofibrils, which could improve neuron survival by sequestering toxic species of ␣-SN. In this context, our results could pave the way for a novel therapeutic strategy on neurodegenerative diseases
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