Mariana Gallo | Huntingtin’s N17 region: Post-translational modifications

Mariana Gallo, University of Parma, Italy Huntington’s disease (HD) is a fatal neurodegenerative disorder caused by a polyglutamine (polyQ) expansion in the first exon of the huntingtin protein (HTT exon 1), leading to protein dysfunction and the formation of toxic N-terminal aggregates. The dimerization of the HTT exon 1 fragment, primarily through the self-association of the first 17 residues (N17), triggers the aggregation pathway, and membrane association further accelerates this process by increasing the local concentration of exon 1. Post-translational modifications (PTMs) in the N17 region modulate both membrane binding and aggregation kinetics; however, their precise molecular effects remain elusive. To elucidate how N17 PTMs influence self-association and membrane interactions—critical steps in HTT pathogenesis—we employed solution nuclear magnetic resonance (NMR) and circular dichroism (CD) spectroscopies. Key N17 PTMs, including loss of the initial methionine, subsequent N-term acetylation at alanine (A2), and phosphorylation at threonine (T3) and serines (S13/S16), were systematically analyzed. Our findings demonstrate that PTMs promoting N17 helicity enhance both dimerization and membrane affinity. Strikingly, T3 phosphorylation—previously reported to inhibit HTT exon 1 aggregation—was found to promote helical conformation and dimer formation. X-ray crystallographic studies revealed an anti-parallel N17 dimer with hydrophobic interfaces dominating stability. T3 phosphorylation preserves core dimer contacts, but likely inhibits progression to nucleation-competent oligomers, decoupling dimer formation from downstream aggregation. This HTT exon 1 dimerization model is thus consistent with the association of N17 dimers and provides insight into the impact of PTMs on HTT aggregation. These findings demonstrate how N17 PTMs modulating helical propensity control early aggregation events. Our integrated NMR-CD-crystallography platform establishes a foundation for dissecting additional N17 PTMs and their pathogenic roles. Critically, these insights reposition T3 phosphorylation as a helicity modulator rather than an aggregation suppressor, revealing a nuanced therapeutic target that stabilizes protective dimers while blocking pathogenic oligomerization in HD. #ISAD2026 #Alzheimers #Dementia #AlzheimersDisease #DementiaResearch #AlzheimersResearch #Neuroscience #NeurodegenerativeDiseases #BrainHealth #Neuroinflammation #Amyloid #TauProtein #Biomarkers #ClinicalResearch #ScientificConference #MedicalConference #InternationalConference #ResearchCollaboration #Innovinc #InnovincConferences #InnovincInternational #ParisConference