Crystal structure of DNA polymerase β with DNA containing the base lesion spiroiminodihydantoin in a templating position.

The first high-resolution crystal structure of spiroiminodihydantoin (dSp1) was obtained in the context of the DNA polymerase β active site and reveals two areas of significance. First, the structure verifies the recently determined S configuration at the spirocyclic carbon. Second, the distortion of the DNA duplex is similar to that of the single-oxidation product 8-oxoguanine. For both oxidized lesions, adaptation of the syn conformation results in similar backbone distortions in the DNA duplex. The resulting conformation positions the dSp1 A-ring as the base-pairing face whereas the B-ring of dSp1 protrudes into the major groove.