and R

and R.S.).. a biologically important activity of DNA glycosylases, shielding the potentially harmful repair intermediate until the enzyme acting downstream in the pathway is usually in place to proceed with the repair process. Consistent with this are reports on the ability of human (AP)-endonuclease, APE1, to stimulate the enzymatic turnover of TDG (Waters et al., 1999) and other DNA glycosylases (Parikh et al., 1998; Hill et al., 2001; Nilsen et al., 2001; Vidal et al., 2001; Yang et al., 2001). However, at least in the cases of human TDG Everolimus (RAD001) and OGG1, this stimulation is best explained by simple competition of the DNA glycosylase and the (AP)-endonuclease for the AP site (Vidal et al., 2001). We set out to identify proteins that physically interact with human TDG and actively modulate its turnover in base release assays. Everolimus (RAD001) Yeast two-hybrid screening revealed the human ubiquitin-like modifiers SUMO-1 and SUMO-3 as specific conversation partners of TDG. Three SUMO proteins have been recognized in mammalian cells that, according to their amino acid sequence divergence, can be grouped into two subclasses, SUMO-1 and SUMO-2/3. All SUMOs are known to change target proteins covalently by an enzymatic pathway analogous to ubiquitin conjugation. Unlike ubiquitylation, however, SUMO conjugation does not lead to protein degradation but provokes other, apparently target protein-specific effects, all modulating biological activities in different ways (examined in Melchior, 2000; Rabbit polyclonal to Catenin T alpha Muller cells. No binding of either of the SUMO proteins was observed in controls with APE1-coated beads. Vice versa, affinity beads coated with protein extracts from cells expressing Everolimus (RAD001) either SUMO-1 or SUMO-3 precipitated recombinant TDG, while control Everolimus (RAD001) beads covered with extract of vector control cells failed to do so (Physique?1C and D). Since these results were reproduced in experiments with purified SUMO proteins (data not shown), it is established that human TDG engages in a direct physical interaction with Everolimus (RAD001) the ubiquitin-like proteins SUMO-1 and SUMO-3. Open in a separate windows Fig. 1. Physical conversation of human TDG with SUMO-1 and SUMO-3. Co-precipitation of purified recombinant human SUMO-1?(A) and SUMO-3?(B) proteins with human TDG. Ni2+-NTA beads coated with 1?g of His6-tagged human TDG protein (lanes?1, 3 and 5) or an equimolar amount of human APE1 (lanes?2, 4 and 6) were incubated with extracts of cells expressing either human SUMO-1 or HA-tagged human SUMO-3 protein. Input (2%), last wash (100%) and bead fractions (100%) were separated by 15% SDSCPAGE and the SUMO proteins detected by western blotting with antibodies against SUMO-1 (A) and the HA-tag (B). SUMO-1 and SUMO-3 precipitated with the TDG (lanes?5) but not with the APE1 beads (lanes?6). Co-precipitation of human TDG with SUMO-1?(C) and SUMO-3?(D) proteins. Affi-Gel?10 beads coated with BL21 extract made up of either SUMO-1 or SUMO-3 (lanes?1, 3 and 5) or no recombinant protein as a control (BL21, lanes?2, 4 and 6) were incubated with recombinant human TDG. Western blotting with a TDG antibody revealed specific binding of TDG to SUMO-1 and SUMO-3 (lanes?5). No binding of TDG to control beads was detected (lanes?6). The input shown (lanes?1 and 2) corresponds to 10% of the total amount of TDG used in the experiment. TDG is the target for modification by ubiquitin-like proteins Since small ubiquitin-like proteins are known to change other cellular proteins covalently, we wondered whether TDG is usually a target for SUMO attachment. Sumoylation is usually a highly dynamic, ATP-dependent and reversible process including activating E1 (AOS1/UBA2) and conjugating E2 enzymes (UBC9) as well as deconjugating ULP isopeptidases (examined in Melchior, 2000; Muller modification of endogenous TDG was detectable following a short incubation of the extract with 10?mM ATP (lane?2). This reaction was stimulated further by the presence of a 60mer GU heteroduplex DNA substrate (lane?3). (D)?Recombinant His6-tagged TDG (6H-TDG) was incubated with HeLa nuclear extract in the absence or presence of 10?mM ATP and GU mismatched DNA. Western blotting revealed that this recombinant protein was modified.