Development of a multitasking fluorescent probe for differentiating G-Quadruplex structures

Abstract G-quadruplexes exhibit extensive structural polymorphism, which are highly related to their biological functions. To date, multitasking probes that can simultaneously discriminate among parallel, antiparallel G-quadruplexes and single-/double-stranded nucleic acids have never been reported. In this study, we designed a probe IZNP-2 based on the photoinduced electron transfer (PeT) mechanism. Conformation analysis firstly revealed that IZNP-2 was a smart probe, of which the fluorescence varied according to its molecular conformations. Then, fluorescence assays demonstrated that IZNP-2 could not only differentiate between parallel and antiparallel G-quadruplexes, but also discriminate antiparallel G-quadruplexes from single-/double-stranded nucleic acids. To understand this multitasking ability, we performed various experiments, including absorption titrations, lifetime experiments, Job plot assays and 2-Ap experiments, to investigate the binding modes, which suggested that IZNP-2 might exhibit “Stretched”, “Semi-stretched” and “Stacked” conformations when targeting different nucleic acid topologies, alleviating the PeT to different extents and thus inducing differentiable fluorescence. Furthermore, we broadened the application of IZNP-2 in discriminating between multimeric and monomeric G-quadruplexes. To the best of our knowledge, such a study provides a first example of developing a multitasking fluorescent probe for differentiating different G-quadruplex structures by exploiting the PeT mechanism.