2023 journal article

Frustration Between Preferred States of Complementary Trinucleotide Repeat DNA Hairpins Anticorrelates with Expansion Disease Propensity

JOURNAL OF MOLECULAR BIOLOGY, 435(10).

By: P. Xu  n, J. Zhang  n, F. Pan n, C. Mahn n, C. Roland n, C. Sagui n, K. Weninger n 

author keywords: single molecule FRET; hairpin slippage; molecular dynamics; kinetics; trinucleotide interrupts; Huntington's disease
MeSH headings : Humans; DNA / genetics; DNA / chemistry; DNA, Complementary; Nucleic Acid Conformation; Trinucleotide Repeat Expansion / genetics; Trinucleotide Repeats; Neurodegenerative Diseases / genetics
TL;DR: Single molecule FRET experiments and molecular dynamics simulations are applied to determine conformational stabilities and slipping dynamics for CAG, CTG, GAC and GTC hairpins to determine Tetraloops and TTG interrupts near the loop in the CTG hairpin stabilize the hairpin against slipping. (via Semantic Scholar)
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Added: May 22, 2023

DNA trinucleotide repeat (TRs) expansion beyond a threshold often results in human neurodegenerative diseases. The mechanisms causing expansions remain unknown, although the tendency of TR ssDNA to self-associate into hairpins that slip along their length is widely presumed related. Here we apply single molecule FRET (smFRET) experiments and molecular dynamics simulations to determine conformational stabilities and slipping dynamics for CAG, CTG, GAC and GTC hairpins. Tetraloops are favored in CAG (89%), CTG (89%) and GTC (69%) while GAC favors triloops. We also determined that TTG interrupts near the loop in the CTG hairpin stabilize the hairpin against slipping. The different loop stabilities have implications for intermediate structures that may form when TR-containing duplex DNA opens. Opposing hairpins in the (CAG) ∙ (CTG) duplex would have matched stability whereas opposing hairpins in a (GAC) ∙ (GTC) duplex would have unmatched stability, introducing frustration in the (GAC) ∙ (GTC) opposing hairpins that could encourage their resolution to duplex DNA more rapidly than in (CAG) ∙ (CTG) structures. Given that the CAG and CTG TR can undergo large, disease-related expansion whereas the GAC and GTC sequences do not, these stability differences can inform and constrain models of expansion mechanisms of TR regions.