The role of cysteines in the structure and function of OGG1.

8-Oxoguanine glycosylase (OGG1) is a base excision repair enzyme responsible for the recognition and removal of 8-oxoguanine, a commonly occurring oxidized DNA modification. OGG1 prevents the accumulation of mutations and regulates the transcription of various oxidative stress-response genes. In addition to targeting DNA, oxidative stress can affect proteins like OGG1 itself, specifically at cysteine residues. Previous work has shown that the function of OGG1 is sensitive to oxidants, with the cysteine residues of OGG1 being the most likely site of oxidation. Due to the integral role of OGG1 in maintaining cellular homeostasis under oxidative stress, it is important to understand the effect of oxidants on OGG1 and the role of cysteines in its structure and function. In this study, we investigate the role of the cysteine residues in the function of OGG1 by mutating and characterizing each cysteine residue. Our results indicate that the cysteines in OGG1 fall into four functional categories: those that are necessary for (1) glycosylase activity (C146 and C255), (2) lyase activity (C140S, C163, C241, and C253), and (3) structural stability (C253) and (4) those with no known function (C28 and C75). These results suggest that under conditions of oxidative stress, cysteine can be targeted for modifications, thus altering the response of OGG1 and affecting its downstream cellular functions.