Catalysis And Application Of Mimic Enzyme Modulated By Nucleic Acid Structure

Since the discovery of natural ribozymes,nucleic acids have not only been a storage and processing medium for genetic information,but also have shown catalytic activity.The versatility of these nucleic acids has propelled many studies toward practical applications,such as biomolecular detection,bioengineering,and nanomedicine.Compared with natural proteases and ribozymes,DNAzymes have many practical advantages.For example,DNAzymes are more chemically and thermally stable than proteases and ribozymes,which makes DNAzymes more suitable for on-site testing and analysis.The cost of DNAzymes has been greatly reduced with the developments of the chemical synthesis technology of DNA.At the same time,photosensitized oxidation has been explored in many fields,such as photodynamic therapy?PDT?and photodynamic antibacterial chemotherapy?PACT?.Although photosensitized reactive oxygen?ROS?has emerging application functions,sometimes problems still exist during the controllable management of the photosensitization process.With the further study of the chemical function of DNA,the characteristics of the selective recognition of DNA make them an excellent regulator of photosensitized oxidation.Therefore,on the basis of the interactions between different photosensitizer ligands and nucleic acid which has a variety of structures,this thesis has developed two nucleic acid-based photooxidation mimic enzymes that provide multiple methods to PDT and biosensors.The main contents are as follows:1.G-Quadruplex-Based Photooxidase Driven by Visible Light.The G-quadruplex?G4?/hemin entity has been widely used as a peroxidase-mimic DNAzyme to catalyze the substrate oxidation with exogenous and concentrated H₂O₂as oxidant for developing various devices.Herein,a G4-based oxidase-mimic DNAzyme that can be driven by visible light was developed.The oxidant is in situ produced by light irradiation.As a natural photosensitizer,Hypericin?Hyp?alone in solution is inactive because of aggregation.However,the binding with G4 triggers the fluorescence emission and activates Hyp to produce singlet oxygen?¹O₂?by energy transfer to the dissolved oxygen.Therefore,the G4/Hyp entity can serve as a photooxidase via the ¹O₂ pathway to catalyze the substrate oxidation.Since the G4-bound Hyp can be excited by almost the whole range of visible light,the photooxidase should cover a wide range of photocatalytic applications.Similar to the peroxidase-mimic DNAzyme,the G4 sequence can regulate the photooxidase activity and metal ions can serve as efficient cofactors to activate the photooxidase capacity for an inactive G4 structure.This work provides an alternative to build a versatile G4-based photooxidase with straightforward tunability of its activity.2.Photocatalytic Duplex DNAzyme with an Abasic Site as Active Site.¹O₂ produced by photosensitization of natural drugs has become increasingly attractive in the development of bioassays and PDT.More and more studies have begun to use DNA to activate photosensitivity with interacting photosensitizers.As an isoquinoline alkaloid,palmatine?PAL?is widely used as a multi-purpose drug with considerable biological activity in pharmacy.Recently,PAL has been proposed as a promising DNA phototherapy drug.Interacting with fully matched double-stranded DNA of a specific sequence can activate its photosensitization.However,the steric hindrance is significantly enhanced when PAL binds to the small groove of DNA and the photosensitive activity is greatly limited.Herein,we first proposed DNA containing an abasic site?AP-DNA?as an excellent regulator for photosensitization of PAL to improve the production capacity of ¹O₂,and developed a photooxidase that can catalyze the oxidation of substrates.At the same time,we used uracil-DNA glycosylase?UDG?to remove uracil from fully matched double-stranded DNA that can generate an AP site.This method is low-cost and the activity of photooxidase is not affected with the UDG addition.