Solution structure of the Oxytricha telomeric repeat d[G4(T4G4)3] G-tetraplex

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biophysics

Background:

• Telomeres protect chromosome ends and are rich in guanine.
• G-quadruplexes are non-canonical DNA structures formed in guanine-rich sequences.
• Understanding G-quadruplex structures is crucial for telomere biology and drug development.

Purpose of the Study:

• To determine the solution structure of the Oxytricha telomere sequence d[G4(T4G4)3].
• To characterize the folding topology, loop conformations, and groove characteristics of the G-quadruplex.
• To compare the structure with other G-quadruplexes, such as the human sequence.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy.
• Molecular dynamics simulations with relaxation matrix refinement.
• Analysis of guanine glycosidic bond orientations and G-tetrad alignments.

Main Results:

• The Oxytricha sequence forms a right-handed G-quadruplex with four stacked G-tetrads.
• The structure features two lateral T4 loops and a central diagonal T4 loop.
• Distinct grooves (two medium-width parallel, one wide and one narrow anti-parallel) are formed.
• Guanine residues exhibit syn-anti alternations, and G-tetrad orientations vary.
• The diagonal loop is well-defined, while lateral loops are flexible.

Conclusions:

• The Na+-stabilized Oxytricha G-quadruplex shares a common folding topology with the human counterpart.
• The conserved features include guanine residue distribution and the central diagonal loop.
• The well-resolved NMR spectra enable further studies on cation effects, hydration, and ligand/protein interactions.