Folding Landscape of a Parallel G-Quadruplex.

ABSTRACT: Circular dichroism and stopped-flow UV spectroscopies were used to investigate the thermodynamic stability and the folding pathway of d[TGAG3TG3TAG3TG3TA2] at 25 °C in solutions containing 25 mM KCl. Under these conditions the oligonucleotide adopts a thermally stable, all-parallel G-quadruplex topography containing three stacked quartets. K+-induced folding shows three resolved relaxation times, each with distinctive spectral changes. Folding is complete within 200 s. These data indicate a folding pathway that involves at least two populated intermediates, one of which seems to be an antiparallel structure that rearranges to the final all-parallel conformation. Molecular dynamics reveals a stereochemically plausible folding pathway that does not involve complete unfolding of the intermediate. The rate of unfolding was determined using complementary DNA to trap transiently unfolded states to form a stable duplex. As assessed by 1D-1H NMR and fluorescence spectroscopy, unfolding is extremely slow with only one observable rate-limiting relaxation time.

SUBMITTER: Gray RD 

PROVIDER: S-EPMC6455816 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature