Recognition and Unfolding of c-MYC and Telomeric G-Quadruplex DNAs by the RecQ C-Terminal Domain of Human Bloom Syndrome Helicase

Abstract

G-quadruplex (G4) is a noncanonical DNA secondary structure formed by Hoogsteen base pairing. It is recognized by various DNA helicases involved in DNA metabolism processes such as replication and transcription. Human Bloom syndrome protein (BLM), one of five human RecQ helicases, is a G4 helicase. While several studies revealed the mechanism of G4 binding and unfolding by the conserved RecQ C-terminal (RQC) domain of BLM, how RQC recognizes different G4 topologies is still unclear. Here, we investigated the interaction of Myc-22­(14/23T) G4 from the c-Myc promoter and hTelo G4 from the telomeric sequence with RQC. Myc-22­(14/23T) and hTelo form parallel and (3+1) hybrid topologies, respectively. Our circular dichroism (CD) spectroscopy data indicate that RQC can partially unfold the parallel G4, even with a short 3′ overhang, while it can only partially unfold the (3+1) hybrid G4 with a 3′ overhang of 6 nucleotides or longer. We found that the intrinsic thermal stability of G4 does not determine RQC-induced G4 unfolding by comparing T m of G4s. We also showed that both parallel and (3+1) hybrid G4s bind to the β-wing region of RQC. Thermodynamic analysis using isothermal titration calorimetry (ITC) showed that all interactions were endothermic and entropically driven. We suggest that RQC partially unfolds the parallel G4 more efficiently than the (3+1) hybrid G4 and binds to various G4 structures using its β-wing region. By this information, our research provides new insights into the influence of G4 structure on DNA metabolic processes involving BLM.

The Amino Acids Motif -32GSSYN36- in the Catalytic Domain of E. coli Flavorubredoxin NO Reductase Is Essential for Its Activity

“…The maximum molar ellipticity values at 225 nm were normalized and fitted to the Boltzmann sigmoidal curve using Origin 2019 software [36]:…”

“…where T m is the melting temperature, dx is the slope of the curve, Y is the molar ellipticity value, x is the temperature and T m is the melting temperature [36].…”

Fuzzy protein theory for disordered proteins

“…Ordered binding modes are achieved via disorder-to-order transitions resulting in well-defined contact patterns between specific residues [13,14]. Disordered binding modes involve many binding configurations, which are resulted by disorder-to-disorder transitions [15][16][17]. In these cases, interactions in the bound state ensemble are mediated by redundant motifs.…”