The MLLE Domain of the Ubiquitin Ligase UBR5 Binds to Its Catalytic Domain to Regulate Substrate Binding

• DOI: 10.1074/jbc.m115.672246
• Publication Date: 2015-07-30T02:54:47Z
• Authors: Juliana Muñoz-Esc...; Edna Matta-Camacho; Guennadi Kozlov; Kalle Gehring
• Keywords: 0303 health sciences; Ubiquitin-Protein Ligases; Amino Acid Motifs; RNA-Binding Proteins; Crystallography, X-Ray; Protein Structure, Tertiary; Rats; 03 medical and health sciences; Peptide Initiation Factors; Animals; Humans; Peptides; Protein Structure, Quaternary; Protein Binding

E3 ubiquitin ligases catalyze the transfer of ubiquitin from an E2-conjugating enzyme to a substrate. UBR5, homologous to the E6AP C terminus (HECT)-type E3 ligase, mediates the ubiquitination of proteins involved in translation regulation, DNA damage response, and gluconeogenesis. In addition, UBR5 functions in a ligase-independent manner by prompting protein/protein interactions without ubiquitination of the binding partner. Despite recent functional studies, the mechanisms involved in substrate recognition and selective ubiquitination of its binding partners remain elusive. The C terminus of UBR5 harbors the HECT catalytic domain and an adjacent MLLE domain. MLLE domains mediate protein/protein interactions through the binding of a conserved peptide motif, termed PAM2. Here, we characterize the binding properties of the UBR5 MLLE domain to PAM2 peptides from Paip1 and GW182. The crystal structure with a Paip1 PAM2 peptide reveals the network of hydrophobic and ionic interactions that drive binding. In addition, we identify a novel interaction of the MLLE domain with the adjacent HECT domain mediated by a PAM2-like sequence. Our results confirm the role of the MLLE domain of UBR5 in substrate recruitment and suggest a potential role in regulating UBR5 ligase activity.