Solution Structure of a CUE-Ubiquitin Complex Reveals a Conserved Mode of Ubiquitin Binding

Abstract

Monoubiquitination serves as a regulatory signal in a variety of cellular processes. Monoubiquitin signals are transmitted by binding to a small but rapidly expanding class of ubiquitin binding motifs. Several of these motifs, including the CUE domain, also promote intramolecular monoubiquitination. The solution structure of a CUE domain of the yeast Cue2 protein in complex with ubiquitin reveals intermolecular interactions involving conserved hydrophobic surfaces, including the Leu8-Ile44-Val70 patch on ubiquitin. The contact surface extends beyond this patch and encompasses Lys48, a site of polyubiquitin chain formation. This suggests an occlusion mechanism for inhibiting polyubiquitin chain formation during monoubiquitin signaling. The CUE domain shares a similar overall architecture with the UBA domain, which also contains a conserved hydrophobic patch. Comparative modeling suggests that the UBA domain interacts analogously with ubiquitin. The structure of the CUE-ubiquitin complex may thus serve as a paradigm for ubiquitin recognition and signaling by ubiquitin binding proteins.

Gp78 Cooperates with RMA1 in Endoplasmic Reticulum-associated Degradation of CFTRΔF508

“…Previous studies have precisely mapped the specific sites of interaction between conserved amino acid side chains of the CUE domain and side chains of ubiquitin (Kang et al, 2003;Prag et al, 2003). The amino acids identified in these previous studies were conserved in the CUE domain of gp78, which suggested that the association of gp78 with CFTR⌬F508 ( Figure 3D) occurs through a ubiquitin moiety.…”

“…Recently, Chen et al (2006) demonstrated that both the E2 binding site and the coupling of ubiquitin to ER degradation (CUE) domain of gp78 are essential for its ubiquitin ligase activity. Although recent biochemical and structural studies have helped define the ubiquitin binding properties of CUE domains (Ponting, 2000;Kang et al, 2003;Prag et al, 2003), the role of the gp78 CUE domain in ubiquitin ligation remains unclear. HRD1 is also a RING finger-dependent ubiquitin ligase, located in the ER, and it is involved in ERAD, in cooperation with Ube2g2 (Kaneko et al, 2002;Nadav et al, 2003;Kikkert et al, 2004).…”

Role of protein ubiquitylation in regulating endocytosis of receptor tyrosine kinases

“…Consistent with the possibility that CUE domains and UIM motifs share functional characteristics, the interaction between the CUE domain and ubiquitin appears to mediate recognition of ubiquitylated cargo, as well as activate Rabex/Vps9 upon cargo binding. In addition, within a CUEubiquitin complex, the branching site of ubiquitin at lysine 48 is 'capped', thereby preventing polyubiquitylation (Kang et al, 2003). Thus, endosomal vesicle fusion may be regulated by cargo, through a mechanism in which binding of the CUE domain to ubiquitylated cargo relieves an autoinhibitory intramolecular interaction.…”

Coordination of Hpr1 and Ubiquitin Binding by the UBA Domain of the mRNA Export Factor Mex67

“…UBA-Mex67 retains several features that in other UBA domains are involved in the interaction with ubiquitin. Thus, residues in both helix H1, loop1, and helix H3 have been reported to interact with ubiquitin in UBA:monoubiquitin complexes (Kang et al, 2003;Mueller et al, 2004;Ohno et al, 2005). Analogous residues are present in Mex67, and they are exposed on the surface.…”