The binding interface between an E2 (UBC9) and a ubiquitin homologue (UBL1)

Human UBC9 is a member of the E2 (ubiquitin conjugation enzyme) family of p roteins. Instead of conjugating to ubiquitin, it conjugates with a ubiquiti n homologue UBL1 (also known as SUMO-1, GMP1, SMTP3, PIC1, and sentrin). UB C9 has been shown to be involved in cell cycle regulation, DNA repair, and p53-dependent processes. The binding interfaces of the UBC9 and UBL1 comple x have been determined by chemical shift perturbation using nuclear magneti c resonance spectroscopy. The binding site of UBL1 resides on the ubiquitin domain, and the binding site of UBC9 is located on a structurally conserve d region of E2, Because the UBC9-UBL1 system shares many similarities with the ubiquitin system in structures and in conjugation with each other and w ith target proteins, the observed binding interfaces may be conserved in Ea -ubiquitin interactions in general.