Ataxin-3 (AT3) is the protein that triggers the inherited neurodegenerative 
disorder spinocerebellar ataxia type 3 when its polyglutamine (polyQ) stretch 
close to the C-terminus exceeds a critical length. AT3 consists of the 
N-terminal globular Josephin domain (JD) and the C-terminal disordered one. It 
cleaves isopeptide bonds between ubiquitin monomers, an event involved in 
protein quality control mechanisms. AT3 has been implicated in the pathway that 
sorts aggregated protein to aggresomes via microtubules, in which dynein and 
histone deacetylase 6 (HDAC6) also seem to be involved. By taking advantage of 
small angle X-ray scattering (SAXS) and surface plasmon resonance (SPR), we have 
investigated the interaction of AT3 with tubulin and HDAC6. Based on SAXS 
results, the AT3 oligomer, consisting of 6-7 subunits, tightly binds to the 
tubulin hexameric oligomer in a "parallel" fashion. By SPR analysis we have 
demonstrated that AT3 binds to tubulin dimer with a 50nM affinity. Binding fits 
with a Langmuir 1:1 model and involves a single binding interface. Nevertheless, 
the interaction surface consists of three distinct, discontinuous 
tubulin-binding regions (TBR), one located in the JD, and the two others in the 
disordered domain, upstream and downstream of the polyQ stretch. In the absence 
of any of the three TBRs, the affinity is drastically reduced. By SPR we have 
also provided the first evidence of direct binding of AT3 to HDAC6, with 
affinity in the range 0.1-1μM. These results shed light on the interactions 
among the components of the transport machinery that sorts aggregate protein to 
the aggresome, and pave the way to in vivo studies aimed at further clarifying 
their roles.