α-Synuclein is a Novel Microtubule Dynamase.

Daniele Cartelli,Jacopo Marangon,Silvia Beltramone,Rita Grandori,Isabelle Arnal,Luigi Bubacco,Carlo Santambrogio,Francesca Cantele,Laurent Roybon,Carmelita De Gregorio,Evelina Chieregatti,Gianni Pezzoli,Alessandro Aliverti,Stefano Pieraccini,Alberto Barbiroli,Marco Emanuele,Staffan Holmqvist,Graziella Cappelletti,V Pandini ,Enzio Ragg ,Francesca Casagrande

doi:10.1038/srep33289

Abstract

α-Synuclein is a presynaptic protein associated to Parkinson’s disease, which is unstructured when free in the cytoplasm and adopts α helical conformation when bound to vesicles. After decades of intense studies, α-Synuclein physiology is still difficult to clear up due to its interaction with multiple partners and its involvement in a pletora of neuronal functions. Here, we looked at the remarkably neglected interplay between α-Synuclein and microtubules, which potentially impacts on synaptic functionality. In order to identify the mechanisms underlying these actions, we investigated the interaction between purified α-Synuclein and tubulin. We demonstrated that α-Synuclein binds to microtubules and tubulin α2β2 tetramer; the latter interaction inducing the formation of helical segment(s) in the α-Synuclein polypeptide. This structural change seems to enable α-Synuclein to promote microtubule nucleation and to enhance microtubule growth rate and catastrophe frequency, both in vitro and in cell. We also showed that Parkinson’s disease-linked α-Synuclein variants do not undergo tubulin-induced folding and cause tubulin aggregation rather than polymerization. Our data enable us to propose α-Synuclein as a novel, foldable, microtubule-dynamase, which influences microtubule organisation through its binding to tubulin and its regulating effects on microtubule nucleation and dynamics.

Highlights

Wild type (WT) Syn promotes MT assembly, whereas Chen and colleagues have claimed that neither monomeric nor oligomeric Syn influences MT polymerization in vitro[10]
In order to investigate the mechanism by which Syn regulates MT cytoskeleton and to determine whether Syn interacts with tubulin dimer or with higher-order assemblies, we studied the interaction between purified Syn and tubulin in vitro
Differential interference contrast (DIC) and fluorescence microscopy analyses confirmed that wild type (WT) Syn co-polymerizes with MTs (Supplementary Fig. S2), as revealed by Syn staining along conventional MTs polymerized in the presence of Syn

Summary

Introduction

Wild type (WT) Syn promotes MT assembly, whereas Chen and colleagues have claimed that neither monomeric nor oligomeric Syn influences MT polymerization in vitro[10]. Co-immunoprecipitation studies as well as affinity chromatography have revealed a direct interaction between Syn and free tubulin[11], but it is still unclear whether Syn forms a complex with tubulin dimers or with higher-order assemblies. We analyse the interaction between Syn and tubulin and we clear up the physiological relevance of the interaction between Syn and MTs. We found that WT Syn undergoes a structural change upon tubulin binding, promoting both microtubule nucleation and dynamics. Our data obtained with PD-related Syn mutants provide hints for the pathogenic mechanism in PD

Methods

Results

Conclusion