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. Author manuscript; available in PMC: 2009 Aug 20.
Published in final edited form as: Chem Rev. 2006 Aug;106(8):3443–3467. doi: 10.1021/cr050317n

Figure 20.

Figure 20

Reaction pathway of UDG. A stepwise mechanism has been established involving a discrete oxacarbenium ion intermediate that is stabilized by electrostatic interactions with active site residues and the phosphodiester groups of the DNA. Two catalytic groups are indicated in the figure: His268, which serves as a hydrogen bond donor to stabilize the developing negative charge on uracil O2 in the dissociative transition state, and Asp145, which stabilizes the cationic sugar of the intermediate. The structure of 1-aza-deoxyribose (1-aza-dR), which is proposed to mimic the sugar conformation in the second transition state involving water addition, is also shown.