NMR and molecular modeling studies of the interaction of artificial AP lyases with a DNA duplex containing an apurinic abasic site model

Tailor-made molecules, DTAc and ATAc, that incorporate a nucleic base (adenine or 2,6-diaminopurine) linked by a diamino chain to an intercalator (9-amino-6-chloro-2-methoxyacridine) selectively recognize and efficiently cleave abasic sites in DNA via a p-elimination reaction. The threedimensional structure of the complexes of DTAc and ATAc bound to a DNA undecamer, the (5')d(C(1)G(2)C(3)A(4)C(5)X(6)C(7)A(8)C(9)G(10)C(11))(3'.3')d(G(22)C(21)G(20)T(19)G(18)T(17)G(16)T(15)G(14)C(13)G(12))(5') duplex in which the X residue is a stable abasic site [3-hydroxy-2-(hydroxymethyl)tetrahydrofuran], has been studied by combined NMR-energy minimization methods. Analysis of the NMR spectra reveals that DTAc and ATAc interact with a very similar fashion and form two different complexes with DNA, present in a ratio of 70/30 (+/-10). In both complexes, the acridine ring intercalates exclusively between the C3.G20 and A4.T19 base pairs, the linker is located in the minor groove, and the base moiety docks in the abasic site. The principal difference between the major and the minor complexes consists of a 180 degrees rotation of the acridine ring around the Acr-C-N bond within the same intercalation site. Molecular modeling studies with few intermolecular ligand-DNA restraints were used to investigate the geometry of the base pair formed between the diaminopurine of DTAc and the T17 ring. The most energetically favored complex has the 2,6-diaminopurine of DTAc base paired with the T17 ring in a Hoogsteen conformation. The models DTAc and ATAc are also discussed as nuclease mimics and cleaving agents at abasic sites.