Abstract
CBL is a RING type E3 ubiquitin ligase that functions as a negative regulator of tyrosine kinase signaling and loss of CBL function is implicated in several forms of leukemia. The Src-like adaptor proteins (SLAP/SLAP2) bind to CBL and are key components of CBL-dependent downregulation of antigen receptor, cytokine receptor, and receptor tyrosine kinase signaling. To understand the molecular basis of the interaction between SLAP/SLAP2 and CBL, we solved the crystal structure of CBL tyrosine kinase binding domain (TKBD) in complex with SLAP2. The carboxy-terminal region of SLAP2 adopts an α-helical structure which binds in a cleft between the 4H, EF-hand, and SH2 domains of the TKBD. This SLAP2 binding site is remote from the canonical TKBD phospho-tyrosine peptide binding site but overlaps with a region important for stabilizing CBL in its autoinhibited conformation. Addition of SLAP2 to autoinhibited CBL in vitro activates CBL autoubiquitination. As well, disruption of the CBL/SLAP2 interface through mutagenesis demonstrates a role for this protein-protein interaction in regulation of CBL E3 ligase activity in cells. Our results reveal that SLAP2 binding provides an alternative mechanism for activation of CBL ubiquitin ligase function.
Competing Interest Statement
The authors have declared no competing interest.