Energy minimized structures of carcinogen-dna adducts: 2-acetylaminofluorene and 2-aminofluorene

Energy minimized structures of DNA modified by the aromatic amines 2-acetylaminofluorene (AAF) and 2-aminofuorene (AF), for which no experimental atomic resolution data exist, are presented. These have been computed with a new molecular mechanics program specifically designed to define distortions imposed by such adducts, and employing a rational strategy for searching the conformation space of a DNA molecule with covalently linked carcinogen. In alternating G-C sequences, the AAF adduct prefers to reside at the exterior of an undeformed Z-helix. It can also induce base displacement with attendant denaturation and helix bending in sequences that disfavor the Z form, but undeformed B helices are excluded. The AF adduct, by contrast, prefers the major groove of an unperturbed B-helix, but can also induce carcinogen-base stacking in single stranded regions of the DNA, such as at the replication fork. The different biological properties of these two adducts may be related to their distinct conformational features.