How loop lengths shape topological preferences of two-tetrad G-quadruplexes.

Area of Science:

• Molecular Biology
• Genomics
• Biophysics

Background:

• Smallest G-quadruplex (G4) structures involve two G-tetrads.
• These simple G4 motifs are prevalent in the human genome.
• G4s play roles in gene regulation and disease.

Purpose of the Study:

• To systematically analyze how loop length influences the structural preferences of two-tetrad G4s.
• To define characteristics of two-tetrad G4s and distinguish them from higher-order structures.
• To map sequence space for G4 folds based on molecularity and loop topology.

Main Methods:

• Experimental characterization of 64 DNA sequences (5'-GGTx=1-4GGTy=1-4GGTz=1-4GG-3').
• Utilized biophysical methods to differentiate two-tetrad G4s from higher-order assemblies.
• Employed 2D Nuclear Magnetic Resonance (NMR) for loop topology assignment.

Main Results:

• Identified features characteristic of two-tetrad G4 structures.
• Assigned specific loop topologies for 17 two-tetrad folds.
• Found the +l+l+l (antiparallel-chair) topology to be most prevalent, followed by -ld+l (antiparallel-basket).

Conclusions:

• The length of the central loop is the main determinant of two-tetrad G4 structural preferences.
• The study delineates sequence space occupied by G4 folds of different molecularities and loop topologies.
• Understanding these relationships is key for studying G4 roles in biological processes.