Studies On Interface Assembly Of Nucleic Acid Substructure And Ligand Recognition

Organism genome contains a large number of non-classical G-quadruplex-forming sequences,and the role of G-quadruplexes in organisms is crucial.In particular,the high-order multimeric G-quadruplex?G4?structure has attracted much attention due to its biological activity in vivo,application in cancer treatment,sensor signal amplification and biocatalysis.In the thesis,the main research objects are the assembly characteristics of the interface between G-quadruplex substructures and ligand recognition.Firstly,porphyrin molecules were used as probes to study the multicolor fluorescence recognition of the stacked and unstacked interfaces between G-quadruplex substructures.Secondly,the induction effect of multivalent metal cerium ions on the formation of high-order assembly dimers of human telomere G-quadruplex monomers was investigated and it was found that the high-order assembly can activate the catalytic activity of cerium ions.The main research contents are as follows:1.Multicolorfully probing intramolecular G-quadruplex tandem interfaceA long guanine-rich sequence can form multiple G-quadruplex?G4?tandem individuals in a single molecule with internal G4-G4?in G4-G4?interfaces.The interfaces can stay at the stacked?s-in G4-G4?and unstacked?us-in G4-G4?states,dependent of the G4 conformations and environments.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 with an interface-dependent manner.Herein,we found that a porphyrin with four dihydroxyphenyl substituents?OH₂PP?can multicolorfully recognize the s-in G4-G4dimer interface against the us-in G4-G4 dimer one.The s-in G4-G4 dimer cause significant red shifts in the excitation and emission bands of OH₂PP in contrast to the us-in G4-G4 dimer and G4 monomer with a negligible wavelength shift.OH₂PP adopts a 1:1 binding mode with the s-in G4-G4 dimer,whereas a 2:1 binding mode occurs to the us-in G4-G4 dimer.The limit of detection?LOD?for s-in G4-G4structures is about tens of n M level.The observed binding dependence of OH₂PP on the linker length between the G4 individuals suggests the interface binding with the s-in G4-G4 dimer.Deformation of the porphyrin macrocycle within the s-in G4-G4interface confinement most likely contributes to the multicolorful response by leading to 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.2.Peroxidase-like activity of G4 assembly induced by Ce³⁺There are many ways to form G-quadruplex assemblies,among which metal ions can induce G-quadruplexes to form multimers that are widely used in the construction of sensor platforms.Therefore,exploring the influence of metal ions on the G-quadruplex has a crucial role.We find that lanthanide trivalent cerium ion can bind to human telomere G-quadruplex ht G4 with a binding ratio of 1:2 and induces ht G4 to form higher-order dimers.The binding site of cerium ion to ht G4 is at the G-quadruplex dimer G4-G4 interface,which can form a G4/Ce³⁺/G4 complex.More interestingly,we found that the G4/Ce³⁺/G4 complex has a certain catalase activity and can catalyze the oxidation of TMB?3,3,5,5-tetramethylbenzidine?with hydrogen peroxide.The pseudoenzymatic activity of the G4/Ce³⁺/G4 complex is likely related to the accelerated conversion rate between Ce³⁺and Ce⁴⁺in the complex.Our work shows that the combination of nucleic acids and cerium ions to form higher-order assemblies with pseudoenzymatic activity,which provides more feasibility for the application of cerium complexes in the biological field.At the same time,it provides new possibilities for the formation of higher-order assembled G-quadruplexes.