The cellular protein nucleolin preferentially binds long-looped G-quadruplex nucleic acids

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• G-quadruplexes (G4s) are non-canonical DNA structures crucial in cellular mechanisms.
• Nucleolin (NCL) is a protein implicated in diseases like neurodegeneration and cancer through its interaction with G4s.
• Understanding NCL-G4 interactions is key to deciphering disease pathways.

Purpose of the Study:

• To define the molecular determinants of Nucleolin (NCL) binding to G-quadruplexes (G4s).
• To elucidate how NCL-G4 interactions influence the structure and function of G4s.
• To provide insights into the role of NCL-G4 complexes in pathological processes.

Main Methods:

• Electrophoresis mobility shift assay (EMSA) for detecting NCL/G4 binding.
• Circular dichroism (CD) spectroscopy for assessing G4 folding, topology, and stability.
• Dimethylsulfate (DMS) footprinting to identify G-bases involved in G4 folding.

Main Results:

• NCL binding to G4s is primarily dependent on G4 loop length, irrespective of conformation or sequence.
• NCL preferentially binds to less stable G4 structures.
• When alternative conformations exist, NCL favors those with longer loops, even if it requires sparing G-tracts from folding.

Conclusions:

• NCL-G4 binding determinants, particularly loop length, offer insights into G4 regulatory roles in disease.
• NCL's ability to induce G4 folding suggests a role in cellular mechanosensing and signaling.
• Targeted therapies can be developed by understanding these NCL-G4 regulatory interactions.