DEAD-box RNA helicase Dbp2 binds to G-quadruplex nucleic acids and regulates different conformation of G-quadruplex DNA

G-quadruplexes (G4s) are important in regulating DNA replication, repair and RNA transcription through interactions with specialized proteins. Dbp2 has been identified as a G4 DNA binding protein from Saccharomyces cerevisiae cell lysates. The majority of G4 motifs in Saccharomyces cerevisiae display 5-50 nt loops, only a few have 1-2 nt loops. Human DDX5 could unfold MycG4 DNA, whether Dbp2 also participates in remodeling G4 motifs with short loops in Saccharomyces cerevisiae remains elusive. Here we find that Dbp2 prefers G-rich substrates and binds MycG4 with a high affinity. Dbp2 possesses a dual function for different conformations of MycG4, destabilizing the folded MycG4 and inducing further folding of the unfolded MycG4. Similarly, DDX5 can unfold MycG4, but it exhibits a weaker MycG4 folding-promoting activity relative to Dbp2. Furthermore, Dbp2 facilitates DNA annealing activity in the absence of ATP, suggesting that Dbp2 can work on DNA substrates and possibly participate in DNA metabolism. Our results demonstrate that Dbp2 plays an important role in regulating the folding and unfolding activities of MycG4.