(A) Effect of S13 and/or S16 phosphorylation on HTTex1 aggregation. HTTex1 forms a tadpole-like monomer structure and N17-driven interaction may further drive HTTex1 oligomerization and fibril formation. Phosphorylation at S13 and S16 destabilizes the helix at N17 that leads to inhibition of the formation of HTTex1 fibrils. 