posted on 2020-03-19, 18:48authored byAbhijit Saha, Patricia Duchambon, Vanessa Masson, Damarys Loew, Sophie Bombard, Marie-Paule Teulade-Fichou
We investigate herein
the interaction between nucleolin (NCL) and
a set of G4 sequences derived from the CEB25 human minisatellite that
adopt a parallel topology while differing in the length of the central
loop (from nine nucleotides to one nucleotide). It is revealed that
NCL strongly binds to long-loop (five to nine nucleotides) G4 while
interacting weakly with the shorter variants (loop with fewer than
three nucleotides). Photo-cross-linking experiments using 5-bromo-2′-deoxyuridine
(BrU)-modified sequences further confirmed the loop-length dependency,
thereby indicating that the WT-CEB25-L191 (nine-nucleotide loop) is
the best G4 substrate. Quantitative proteomic analysis (LC-MS/MS)
of the product(s) obtained by photo-cross-linking NCL to this sequence
enabled the identification of one contact site corresponding to a
15-amino acid fragment located in helix α2 of RNA binding domain
2 (RBD2), which sheds light on the role of this structural element
in G4-loop recognition. Then, the ability of a panel of benchmark
G4 ligands to prevent the NCL–G4 interaction was explored.
It was found that only the most potent ligand PhenDC3 can inhibit
NCL binding, thereby suggesting that the terminal guanine quartet
is also a strong determinant of G4 recognition, putatively through
interaction with the RGG domain. This study describes the molecular
mechanism by which NCL recognizes G4-containing long loops and leads
to the proposal of a model implying a concerted action of RBD2 and
RGG domains to achieve specific G4 recognition via a dual loop–quartet
interaction.