Structural insights into substrate recognition by the SOCS2 E3 ubiquitin ligase

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Suppressor of cytokine signaling 2 (SOCS2) is a key component of the Cullin5 E3 ubiquitin ligase complex.
• SOCS2 recognizes phosphotyrosine-modified substrates for ubiquitination and proteasomal degradation.
• The precise molecular mechanisms of SOCS2 substrate recognition remain largely unknown.

Purpose of the Study:

• To elucidate the molecular basis of substrate recognition by SOCS2.
• To determine the structural interactions between SOCS2 and its phosphorylated peptide substrates.
• To investigate the impact of cancer-associated single nucleotide polymorphisms (SNPs) on SOCS2 substrate binding.

Main Methods:

• Co-crystal structure determination of SOCS2-ElonginB-ElonginC complexed with phosphorylated peptides from GHR and EpoR.
• X-ray crystallography at 1.98 Å and 2.69 Å resolution.
• Biophysical assays to assess substrate-binding affinity.

Main Results:

• Co-crystal structures revealed that phosphorylated peptides from GHR and EpoR bind to SOCS2 in an extended conformation, mimicking the SH2 domain-pY interaction.
• Specific hydrophobic interactions involving the EF loop of SOCS2 were identified, contributing to substrate binding.
• The flexible BG loop of SOCS2 was structurally defined but did not directly interact with the substrate degron.
• Cancer-associated SNPs in the pY pocket region were shown to reduce SOCS2 substrate-binding affinity.

Conclusions:

• SOCS2 substrate recognition involves specific interactions with phosphotyrosine-containing peptides, with the EF loop playing a role in specificity.
• The structural data provides a molecular blueprint for understanding SOCS2 function in cytokine signaling regulation.
• Insights into how cancer mutations affect SOCS2 binding can inform the development of targeted therapeutics.