Random Formation of G-Quadruplexes in the Full-Length Human Telomere Overhangs Leads to a Kinetic Folding Pattern with Targetable Vacant G-Tracts

Punnoose, Jibin Abraham; Ma, Yue; Hoque, Mohammed Enamul; Cui, Yunxi; Sasaki, Satoshi; Guo, Athena Huixin; Mao, Hanbin

doi:10.1021/acs.biochem.8b00957

Cited by 33 publications

(20 citation statements)

References 61 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Molecular dynamics simulations combined with sedimentation velocity and fluorescence measurements supported the conclusion that oligonucleotides consisting of 8 or 12 telomeric repeats form primarily into 2 or 3 consecutive hybrid-type G-quadruplexes, respectively, with no gaps between them [ 104 , 105 ]. On the other hand, a single-molecule force ramping assay using oligonucleotides ranging from 4 to 12 repeats supported an alternative scenario, in which G-quadruplexes randomly form along the sequence and may have single-stranded telomere repeats between them [ 106 ]. Visualization of the behavior of very long single-stranded telomeric DNA (100 nt–20 kb) by electron microscopy supports the existence of single-stranded regions between G-quadruplexes [ 82 ].…”

Section: G-quadruplexes In the Telomeric Single-stranded Overhangmentioning

confidence: 99%

G-Quadruplexes at Telomeres: Friend or Foe?

Bryan

2020

Molecules

140

View full text Add to dashboard Cite

Telomeres are DNA-protein complexes that cap and protect the ends of linear chromosomes. In almost all species, telomeric DNA has a G/C strand bias, and the short tandem repeats of the G-rich strand have the capacity to form into secondary structures in vitro, such as four-stranded G-quadruplexes. This has long prompted speculation that G-quadruplexes play a positive role in telomere biology, resulting in selection for G-rich tandem telomere repeats during evolution. There is some evidence that G-quadruplexes at telomeres may play a protective capping role, at least in yeast, and that they may positively affect telomere maintenance by either the enzyme telomerase or by recombination-based mechanisms. On the other hand, G-quadruplex formation in telomeric DNA, as elsewhere in the genome, can form an impediment to DNA replication and a source of genome instability. This review summarizes recent evidence for the in vivo existence of G-quadruplexes at telomeres, with a focus on human telomeres, and highlights some of the many unanswered questions regarding the location, form, and functions of these structures.

show abstract

Section: G-quadruplexes In the Telomeric Single-stranded Overhangmentioning

confidence: 99%

G-Quadruplexes at Telomeres: Friend or Foe?

Bryan

2020

Molecules

140

View full text Add to dashboard Cite

show abstract

“…Specifically, the formation of G-quadruplex (GQ) structures has been shown to affect the replication of telomeres 3 and telomerase catalysis 4 . GQs are nucleic acid structures that are formed by four single stranded telomeric repeats 5 , 6 . To compensate for telomeric DNA lost during DNA replication, continuously proliferating cells such as germ cells, stem cells, and most cancer cells express telomerase 1 .…”

Section: Introductionmentioning

confidence: 99%

Observation of processive telomerase catalysis using high-resolution optical tweezers

et al. 2020

View full text Add to dashboard Cite

Telomere maintenance by telomerase is essential for continuous proliferation of human cells and is vital for the survival of stem cells and 90% of cancer cells. To compensate for telomeric DNA lost during DNA replication, telomerase processively adds GGTTAG repeats to chromosome ends by copying the template region within its RNA subunit. Between repeat additions, the RNA template must be recycled. How telomerase remains associated with substrate DNA during this critical translocation step remains unknown. Using a newly developed single-molecule telomerase activity assay utilizing high-resolution optical tweezers, we demonstrate that stable substrate DNA binding at an anchor site within telomerase facilitates the processive synthesis of telomeric repeats. The product DNA synthesized by telomerase can be recaptured by the anchor site or fold into G-quadruplex structures. Our results provide detailed mechanistic insights into telomerase catalysis, a process of critical importance in aging and cancer.

show abstract

“…For longer sequences with three and four G4 units, a mixture of hybrid-2 and hybrid-1 conformations seems to be present in an approximate 3:1 ratio. Our results show unequivocally that for all sequences up to 96 nt in length, the human telomere sequence maximizes its G4 formation, leaving no gaps-in direct contrast to prior EM, AFM, and single-molecule force ramping investigations (38)(39)(40). Our results provide the first quantitative estimates of the rigidity of folded telomeric DNA through determination of its persistence length (Lp = ~34 Å).…”

Section: Discussionmentioning

confidence: 52%

The solution structures of higher-order human telomere G-quadruplex multimers

Monsen

Chakravarthy

Dean

et al. 2020

Preprint

View full text Add to dashboard Cite

Human telomeres contain the repeat DNA sequence 5’(TTAGGG), with duplex regions that are several kilobases long terminating in a 3’ single-stranded overhang. The structure of the single-stranded overhang is not known with certainty, with disparate modes proposed in the literature. We report here the results of an integrated structural biology approach that combines small-angle X-ray scattering, circular dichroism (CD), analytical ultracentrifugation, size-exclusion column chromatography and molecular dynamics simulations that provide the most detailed characterization to date of the structure of the telomeric overhang. We find that the single-stranded sequences 5’(TTAGGG)n, with n=8, 12, and 16, fold into multimeric structures containing the maximal number (2, 3, and 4, respectively) of contiguous G4 units with no long gaps between units. The G4 units are a mixture of hybrid-1 and hybrid-2 conformers. In the multimeric structures, G4 units interact, at least transiently, at the interfaces between units to produce distinctive CD signatures. Global fitting of our hydrodynamic and scattering data to a worm-like chain (WLC) model indicates that these multimeric G4 structures are semi-flexible, with a persistence length of about 34 Å. Investigations of its flexibility using MD simulations reveal stacking, unstacking, and coiling movements, which yield unique sites for drug targeting.

show abstract

Random Formation of G-Quadruplexes in the Full-Length Human Telomere Overhangs Leads to a Kinetic Folding Pattern with Targetable Vacant G-Tracts

Cited by 33 publications

References 61 publications

G-Quadruplexes at Telomeres: Friend or Foe?

G-Quadruplexes at Telomeres: Friend or Foe?

Observation of processive telomerase catalysis using high-resolution optical tweezers

The solution structures of higher-order human telomere G-quadruplex multimers

Contact Info

Product

Resources

About