Fig. 5

A close up view of the 10R (+)- and 10S (−)-cis-BP-N ²-dG adducts within Rev1 and comparisons with the 10S (+)-trans-BP structure. a Contacts of the 10S (−)-cis-BP-N ²-dG adduct with the Rev1 protein. The BP-modified dG forms hydrogen bonds between the N7 and O ⁶ atoms at its Hoogsteen edge and the main-chain amides of Met685 and Gly686 of Rev1. There is also a water-mediated bond between the O ⁶ of the base and the peptide amide of Lys681. The C9-OH of the BP moiety forms hydrogen bonds with the side chains of Trp417 and Asp399 and the C8-OH group of the BP is bridged to the N1 of the dG base through a water molecule. b Comparison of the 10R (+)-cis-BP-N ²-dG and 10S (+)-trans-BP adduct alignments. The 10R (+)-cis-BP-dG (shown in beige colored sticks) in the complex with Rev1 is superpositioned on the 10S (+)-trans-BP adduct structure (shown in orange sticks); the structures are aligned by Rev1 protein chains. The 10S ( + )-trans-BP and 10R (+)-cis-BP- moieties are oriented in the opposite directions. However, they occupy approximately the same physical space in the Rev1 active site. c A simulated annealing Fo−Fc omit map (contoured at 3.0σ-level at 2.24 Å resolution and colored in blue) showing clear electron density of the (−)-cis-BP-modified dG base (magenta sticks). Slight change in the position of the modified dG base (as compared to the unmodified dG as shown in Fig. 3a) places the N3 atom 3.6 Å away from the water molecule that is firmly coordinated via the side chains of Asp399, Trp417, and Lys681 -too far for a hydrogen bond formation. Despite the reasonably high 2.24 Å resolution, the electron density map for the BP moiety is not well defined and the conformation of the adduct cannot be established unambiguously. However, there is a residual electron density of the BP moiety below the dG base