Multicolorfully Probing Intramolecular G-Quadruplex Tandem Interface

A long guanine-rich oliogonucleotide sequence can form multiple G-quadruplex (G4) tandem individuals in a single molecule with internal G4-G4 (inG4-G4) interfaces. The interface can exist at the stacked (s-inG4-G4) or unstacked (us-inG4-G4) state, dependent of the G4 conformation and environment. Because of the vital bioactivity of the G4 interface state, there is a great demand for developing a reliable multicolor fluorescence method to identify the interface state using a fluorophore that can emit at the individual wavelength for a specific interface. Herein, we found that a porphyrin with four dihydroxyphenyl substituents (OH2PP) can multicolorfully recognize the s-inG4-G4 dimer interface against the us-inG4-G4 dimer one. The s-inG4-G4 dimer cause significant red shifts in the excitation and emission bands of OH2PP in contrast to the us-inG4-G4 dimer and G4 monomers. OH2PP adopts a 1:1 binding mode with the s-inG4-G4 dimer, whereas a 2:1 binding mode occurs to the us-inG4-G4 dimer. The limit of detection (LOD) for the s-inG4-G4 structure is about tens of nM level. The observed binding dependence of OH2PP on the linker length between the G4 individuals suggests the interface binding with the s-inG4-G4 dimer. Deformation of the porphyrin macrocycle within the s-inG4-G4 interface confinement most likely contributes to the multicolorful response with the hyperporphyrin effect. Our work demonstrates that OH2PP is a promising fluorophore to fluorescently recognize the G4 multimer with an ideal interface-sensitive multicolor response.