A General Strategy to Access Structural Information at Atomic Resolution in Polyglutamine Homorepeats

Homorepeat (HR) proteins are involved in key biological processes and multiple pathologies, however their high‐resolution characterization has been impaired due to their homotypic nature. To overcome this problem, we have developed a strategy to isotopically label individual glutamines within HRs by combining nonsense suppression and cell‐free expression. Our method has enabled the NMR investigation of huntingtin exon1 with a 16‐residue polyglutamine (poly‐Q) tract, and the results indicate the presence of an N‐terminal α‐helix at near neutral pH that vanishes towards the end of the HR. The generality of the strategy was demonstrated by introducing a labeled glutamine into a pathological version of huntingtin with 46 glutamines. This methodology paves the way to decipher the structural and dynamic perturbations induced by HR extensions in poly‐Q‐related diseases. Our approach can be extended to other amino acids to investigate biological processes involving proteins containing low‐complexity regions (LCRs).