Fig. 1

The stability of the androgen receptor (AR) polyQ helix increases upon tract expansion. a Sequences of the uQ₂₅, uL₄Q₂₅, and L₄Q_n peptides used in this work. b Circular dichroism (CD) spectra of peptides L₄Q₄ to L₄Q₂₅ measured at pH 7.4 and 277 K and plot of the helicity determined by CD as a function of the size of the polyQ tract length, n (inset, color coded). c Residue-specific helicity of peptides L₄Q₄ to L₄Q₂₀ obtained from an analysis of the backbone chemical shifts measured by nuclear magnetic resonance (NMR) at pH 7.4 and 278 K by using the algorithm δ2D²⁸ with an indication of the region of sequence corresponding to the polyQ tract and of its first residue