Structural and Functional Analyses of the Interaction Between the USP7-NTD and the E2-Conjugating Enzymes, UbE2E2 and UbE2E3

Ubiquitin-specific protease 7 (USP7) is a deubiquitinating enzyme that regulates the turnover of proteins in a cell. To date several interacting partners that are involved in various cellular processes have been identified for USP7. Many of the interacting partners of USP7 contain a P/AxxS motif. We have identified two E2 ubiquitin-conjugating enzymes, UbE2E2 and UbE2E3, which contain the P/AxxS motif. Using a co-immunoprecipitation assay we have shown that these E2 proteins interact with USP7 through their P/AxxS motif. Co-crystal structures of the N-terminal domain of USP7 (USP7-NTD) and the E2 peptides reveal that the interactions are formed between USP7-NTD residues 164DWGF167 and the E2 P/AxxS motifs. It has also been established that USP7 may be involved in regulating the cellular levels of UbE2E2. Overall, our findings suggest USP7, a de-ubiquitinating enzyme, is a regulator of ubiquitin-conjugating enzymes, which are involved in the ubiquitination cascade.