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-aminofluorene (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