Paper
Molecular Dynamics Simulations Reveal PolyQ-Length-Dependent Conformational Changes in Huntingtin Exon-1: Implications for Environmental Co-Solvent Modulation of Aggregation-Prone States
Authors
Jai Geddes-Nelson, Xiaochen Liu, Ken-Tye Yong
Abstract
Huntington's disease (HD) is caused by CAG-repeat expansion in HTT, which lengthens the polyglutamine (polyQ) tract in huntingtin (HTT) and promotes misfolding and aggregation. While polyQ-length-dependent aggregation is well established, the atomistic conformational dynamics preceding aggregation remain less defined. Here we perform all-atom molecular dynamics simulations of HTT exon-1 constructs containing the N17 domain, polyQ tracts of clinically relevant lengths (Q21, wildtype; Q40, adult onset threshold; Q70, juvenile onset), and the polyproline (polyP) region. Multi-copy simulations (four chains) were run for 100 ns in explicit SPC/E water using the OPLS-AA force field. We quantified radius of gyration (Rg), solvent-accessible surface area (SASA), root-mean-square deviation (RMSD), and intra-protein hydrogen bonds as proxies for conformational expansion and aggregation propensity. PolyQ expansion drove progressive increases in Rg and SASA, consistent with more extended, solvent-exposed ensembles. We further tested organic co-solvents (methanol, hexane, trichloroethylene; 0.5 to 1.0 M), which modulated these landscapes in a solvent-dependent manner. Trichloroethylene induced marked expansion in Q21 and Q40, whereas methanol produced mild compaction in Q21. To our knowledge, this is the first MD study to systematically examine co-solvent effects on HTT exon-1 conformational dynamics. Although limited sampling precludes definitive mechanistic conclusions, the observed trends suggest that hydrophobic co-solvents can bias HTT exon-1 toward more expanded ensembles, motivating computational studies of gene-environment modulation in HD.
Metadata
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"raw_xml": "<entry>\n <id>http://arxiv.org/abs/2603.02572v1</id>\n <title>Molecular Dynamics Simulations Reveal PolyQ-Length-Dependent Conformational Changes in Huntingtin Exon-1: Implications for Environmental Co-Solvent Modulation of Aggregation-Prone States</title>\n <updated>2026-03-03T03:45:26Z</updated>\n <link href='https://arxiv.org/abs/2603.02572v1' rel='alternate' type='text/html'/>\n <link href='https://arxiv.org/pdf/2603.02572v1' rel='related' title='pdf' type='application/pdf'/>\n <summary>Huntington's disease (HD) is caused by CAG-repeat expansion in HTT, which lengthens the polyglutamine (polyQ) tract in huntingtin (HTT) and promotes misfolding and aggregation. While polyQ-length-dependent aggregation is well established, the atomistic conformational dynamics preceding aggregation remain less defined. Here we perform all-atom molecular dynamics simulations of HTT exon-1 constructs containing the N17 domain, polyQ tracts of clinically relevant lengths (Q21, wildtype; Q40, adult onset threshold; Q70, juvenile onset), and the polyproline (polyP) region. Multi-copy simulations (four chains) were run for 100 ns in explicit SPC/E water using the OPLS-AA force field. We quantified radius of gyration (Rg), solvent-accessible surface area (SASA), root-mean-square deviation (RMSD), and intra-protein hydrogen bonds as proxies for conformational expansion and aggregation propensity. PolyQ expansion drove progressive increases in Rg and SASA, consistent with more extended, solvent-exposed ensembles. We further tested organic co-solvents (methanol, hexane, trichloroethylene; 0.5 to 1.0 M), which modulated these landscapes in a solvent-dependent manner. Trichloroethylene induced marked expansion in Q21 and Q40, whereas methanol produced mild compaction in Q21. To our knowledge, this is the first MD study to systematically examine co-solvent effects on HTT exon-1 conformational dynamics. Although limited sampling precludes definitive mechanistic conclusions, the observed trends suggest that hydrophobic co-solvents can bias HTT exon-1 toward more expanded ensembles, motivating computational studies of gene-environment modulation in HD.</summary>\n <category scheme='http://arxiv.org/schemas/atom' term='cs.CE'/>\n <category scheme='http://arxiv.org/schemas/atom' term='q-bio.BM'/>\n <published>2026-03-03T03:45:26Z</published>\n <arxiv:primary_category term='cs.CE'/>\n <author>\n <name>Jai Geddes-Nelson</name>\n </author>\n <author>\n <name>Xiaochen Liu</name>\n </author>\n <author>\n <name>Ken-Tye Yong</name>\n </author>\n </entry>"
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