Unveiling transient protein-protein interactions that modulate inhibition of alpha-synuclein aggregation by beta-synuclein, a pre-synaptic protein that co-localizes with alpha-synuclein.

Maria K Janowska,Jean Baum,Kuen-Phon Wu

doi:10.1038/srep15164

Abstract

Pathology in Parkinson’s disease is linked to self-association of α-Synuclein (αS) into pathogenic oligomeric species and highly ordered amyloid fibrils. Developing effective therapeutic strategies against this debilitating disease is critical and βS, a pre-synaptic protein that co-localizes with αS, can act as an inhibitor of αS assembly. Despite the potential importance of βS as an inhibitor of αS, the nature, location and specificity of the molecular interactions between these two proteins is unknown. Here we use NMR paramagnetic relaxation enhancement experiments, to demonstrate that βS interacts directly with αS in a transient dimer complex with high specificity and weak affinity. Inhibition of αS by βS arises from transient αS/βS heterodimer species that exist primarily in head- to- tail configurations while αS aggregation arises from a more heterogeneous and weaker range of transient interactions that include both head-to-head and head-to-tail configurations. Our results highlight that intrinsically disordered proteins can interact directly with one another at low affinity and that the transient interactions that drive inhibition versus aggregation are distinct by virtue of their plasticity and specificity.

Highlights

One approach to developing effective therapeutic strategies against this debilitating disease is to identify inhibitors of α -synuclein (α S) aggregation
Our results show that the hetero-dimer transient head- to- tail interactions between α S and β -synuclein (β S) are approximately 5 times stronger than the interactions observed in the homo-dimer α S species suggesting that these α S/β S interactions create a kinetic trap which delays or inhibits the formation of α S fibrils
We demonstrate that the monomer species of α S and β S interact directly with one another at specific sites suggesting that inhibition may begin at the very earliest stages of the fibril formation process

Summary

Introduction

One approach to developing effective therapeutic strategies against this debilitating disease is to identify inhibitors of α S aggregation. NMR inter-chain PRE titration experiments previously used on folded proteins[36] are applied here to intrinsically disordered proteins. These experiments allow us to obtain residue specific dissociation constants to inform us about the specificity and affinity of dimer interactions in the different regions of the transient disordered complexes. The novel insight presented in this paper defines residue specific contacts between two intrinsically disordered proteins and links the homo and hetero-complexes with distinct pathways that lead to aggregation versus inhibition

Methods

Results

Conclusion