The article describes the crystal structure of the c-Cbl-UbcH7-ZAP-70 peptide complex, which reveals how the RING domain of c-Cbl recruits the E2 ubiquitin-conjugating enzyme (E2). The structure shows that the RING domain and the linker sequence pack extensively with the TKB domain, and both domains interact with the UbcH7 E2. The RING domain forms a shallow groove that accommodates the UbcH7 L1 and L2 loops, while the linker helix packs with the H1 helix of UbcH7. The structure also reveals a conserved surface channel leading from the peptide to the E2 active site, suggesting that RING E3s may function as scaffolds that position the substrate and the E2 optimally for ubiquitin transfer. Comparison with the structure of an HECT family E3-E2 complex indicates that a common E2 motif is recognized by both E3 families. The findings provide insights into the specificity of E2-E3 interactions and the mechanism of RING E3-mediated ubiquitination.The article describes the crystal structure of the c-Cbl-UbcH7-ZAP-70 peptide complex, which reveals how the RING domain of c-Cbl recruits the E2 ubiquitin-conjugating enzyme (E2). The structure shows that the RING domain and the linker sequence pack extensively with the TKB domain, and both domains interact with the UbcH7 E2. The RING domain forms a shallow groove that accommodates the UbcH7 L1 and L2 loops, while the linker helix packs with the H1 helix of UbcH7. The structure also reveals a conserved surface channel leading from the peptide to the E2 active site, suggesting that RING E3s may function as scaffolds that position the substrate and the E2 optimally for ubiquitin transfer. Comparison with the structure of an HECT family E3-E2 complex indicates that a common E2 motif is recognized by both E3 families. The findings provide insights into the specificity of E2-E3 interactions and the mechanism of RING E3-mediated ubiquitination.