Mimicking Functions of Native Enzymes or Photosynthetic Reaction-Centers by Nucleoapzymes and Photonucleoapzymes.

The covalent linkage of catalytic units to aptamers-sequence-specific nucleic acids exhibiting selective binding affinities towards substrates leads to functional scaffolds mimicking native enzymes - nucleoapzymes. The binding of the substrates to the aptamer and their structural orientation in respect to the catalytic units duplicates the functions of the active center of enzymes. The possibility to link the catalytic sites directly, or through spacer units, to the 5'-end, 3'-end, and middle positions of the aptamers allows the design of nucleoapzyme libraries, revealing structure-functions diversities, and these can be modelled by molecular dynamics simulations. Catalytic sites integrated into nucleoapzymes include DNAzymes, transition metal complexes and organic ligands. Catalytic transformations driven by nucleoapzymes are exemplified with the oxidation of dopamine or L-arginine, hydroxylation of tyrosine to L-DOPA, hydrolysis of ATP and cholic acid modified esters. The covalent linkage of photosensitizers to the tyrosinamide aptamer leads to a photonucleoapzyme scaffold that binds the N-methyl-N'-(3-aminopropane)-4,4'-bipyridinium-functionalized tyrosinamide to the aptamer. By linking the photosensitizer directly, or through a spacer bridge to the 5'-end or 3'-end of the aptamer, a library of supramolecular photosensitizer/electron acceptor photonucleoapzymes mimicking the functions of photosystem I in the photosynthetic apparatus is demonstrated. The photonucleoapzymes catalyze the photoinduced generation of NADPH, in the presence of ferredoxin-NADP+-reductase (FNR), or the photoinduced H2 evolution catalyzed by Pt nanoparticles. The future perspectives of nucleoapzymes and photonucleoapzymes are discussed.