Dynamics and stability of polymorphic human telomeric G-quadruplex under tension.

Huijuan You,Jie Yan,Xiangjun Zeng,Artem K Efremov,Anh Tuân Phan,Yue Xu,Ci Ji Lim

doi:10.1093/nar/gku581

Abstract

As critical DNA structures capping the human chromosome ends, the stability and structural polymorphism of human telomeric G-quadruplex (G4) have drawn increasing attention in recent years. This work characterizes the equilibrium transitions of single-molecule telomeric G4 at physiological K+ concentration. We report three folded states of telomeric G4 with markedly different lifetime and mechanical stability. Our results show that the kinetically favored folding pathway is through a short-lived intermediate state to a longer-lived state. By examining the force dependence of transition rates, the force-dependent transition free energy landscape for this pathway is determined. In addition, an ultra-long-lived form of telomeric G4 structure with a much stronger mechanical stability is identified.

Highlights

In addition to the canonical double helix B-form structure, DNA can adopt other structures, such as the duplex structures Z-DNA, S-DNA, as well as triplex and tetraplex, etc. [1,2]
A single-stranded telomeric G4 DNA formed on 5 TTGGG(TTAGGG)3TTT sandwiched between two double-stranded DNA (dsDNA) handles was stretched using ultra-stable magnetic tweezers (Figure 1A) [37]
In the subsequent constant loading rate stretching, two types of force responses were observed: (i) If the DNA was in the lower extension state prior to the constant loading rate stretching, an abrupt unfolding transition with a step size of ∼8 nm was observed at a force of ∼20 pN (Figure 1C, first stretching cycle). (ii) If the DNA was in the longer extension state prior to the constant loading rate stretching, such unfolding step was not observed (Figure 1C, second stretching cycle)

Summary

Introduction

In addition to the canonical double helix B-form structure, DNA can adopt other structures, such as the duplex structures Z-DNA, S-DNA, as well as triplex and tetraplex, etc. [1,2]. Increasing evidences have suggested that such structures are ubiquitous in the genome and may play various crucial regulatory functions such as regulation of chromosome stability and gene transcriptions [3,4]. Human telomeric DNA consists of several kilobases of double-stranded DNA (dsDNA) tandem repeats of 5 -TTAGGG sequence, ended with a terminal single-stranded 3 overhang of 100–200 nucleotides [9]. Besides protection of the 3 overhang end of chromosome, telomeric G4 plays a critical role in inhibiting the activity of telomerase [10]. Small molecules stabilizing telomeric G4 have been shown to effectively inhibit telomerase activity and has an anti-cancer activity [13]. The stability of telomeric G4 is crucial for anti-cancer drug developments

Methods

Results

Conclusion