Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 108, Issue 51, Pages 20579-20584Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1110712108
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Funding
- Targeted Proteins Research Program
- matching Program for Innovations in Future Drug Discovery and Medical Care
- Funding Program for World-Leading Innovative R&D on Science and Technology
- Ministry of Education, Science, and Culture, Japan
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Cbl-b is a RING-type E3 ubiquitin ligase that functions as a negative regulator of T-cell activation and growth factor receptor and non-receptor-type tyrosine kinase signaling. Cbl-b dysfunction is related to autoimmune diseases and cancers in humans. However, the molecular mechanism regulating its E3 activity is largely unknown. NMR and small-angle X-ray scattering analyses revealed that the unphosphorylated N-terminal region of Cbl-b forms a compact structure by an intramolecular interaction, which masks the interaction surface of the RING domain with an E2 ubiquitin-conjugating enzyme. Phosphorylation of Y363, located in the helix-linker region between the tyrosine kinase binding and the RING domains, disrupts the interdomain interaction to expose the E2 binding surface of the RING domain. Structural analysis revealed that the phosphorylated helix-RING region forms a compact structure in solution. Moreover, the phosphate group of pY363 is located in the vicinity of the interaction surface with UbcH5B to increase affinity by reducing their electrostatic repulsion. Thus, the phosphorylation of Y363 regulates the E3 activity of Cbl-b by two mechanisms: one is to remove the masking of the RING domain from the tyrosine kinase binding domain and the other is to form a surface to enhance binding affinity to E2.
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