Structural basis for UBA-mediated dimerization of c-Cbl ubiquitin ligase.
Ligand-induced down-regulation by the ubiquitin-protein ligases, c-Cbl and Cbl-b, controls signaling downstream from many receptor-tyrosine kinases (RTK). Cbl proteins bind to phosphotyrosine residues on activated RTKs to affect ligand-dependent ubiquitylation of these receptors targeting them for degradation in the lysosome. Both c-Cbl and Cbl-b contain a ubiquitin-associated (UBA) domain, which is important for Cbl dimerization and tyrosine phosphorylation; however, the mechanism of UBA-mediated dimerization and its requirement for Cbl biological activity is unclear. Here, we report the crystal structure of the UBA domain of c-Cbl refined to 2.1-A resolution. The structure reveals the protein is a symmetric dimer tightly packed along a large hydrophobic surface formed by helices 2 and 3. NMR chemical shift mapping reveals heterodimerization can occur with the related Cbl-b UBA domain via the same surface employed for homodimerization. Disruption of c-Cbl dimerization by site-directed mutagenesis impairs c-Cbl phosphorylation following activation of the Met/hepatocyte growth factor RTK and c-Cbl-dependent ubiquitination of Met. This provides direct evidence for a role of Cbl dimerization in terminating signaling following activation of RTKs.
Kozlov
Guennadi
G
Department of Biochemistry, McGill University.
Peschard
Pascal
P
Department of Biochemistry, McGill University; Molecular Oncology Group, McGill University Health Center, Montréal, Québec H3G 1Y6, Canada.
Zimmerman
Brandon
B
Department of Biochemistry, McGill University.
Lin
Tong
T
Molecular Oncology Group, McGill University Health Center, Montréal, Québec H3G 1Y6, Canada; Department of Medicine, McGill University.
Moldoveanu
Tudor
T
Department of Biochemistry, McGill University.
Mansur-Azzam
Nura
N
Department of Biochemistry, McGill University.
Gehring
Kalle
K
Department of Biochemistry, McGill University; Molecular Oncology Group, McGill University Health Center, Montréal, Québec H3G 1Y6, Canada. Electronic address: kalle.gehring@mcgill.ca.
Park
Morag
M
Department of Biochemistry, McGill University; Molecular Oncology Group, McGill University Health Center, Montréal, Québec H3G 1Y6, Canada; Department of Medicine, McGill University; Department of Oncology, McGill University. Electronic address: morag.park@mcgill.ca.
D000595:Amino Acid Sequence; D019281:Dimerization; D006801:Humans; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D050721:Proto-Oncogene Proteins c-cbl / Q000737:chemistry* / Q000502:physiology; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology; D015398:Signal Transduction; D025801:Ubiquitin / Q000378:metabolism*
D025801:Ubiquitin; D050721:Proto-Oncogene Proteins c-cbl; D020794:Receptor Protein-Tyrosine Kinases; C067419:CBL protein, human