Sequence rules for a long SPOP-binding degron required for protein ubiquitylation

Area of Science:

• Molecular Biology
• Protein Degradation
• Ubiquitination

Background:

• Speckle-type BTB/POZ protein (SPOP) is an adaptor protein crucial for selective protein ubiquitylation by cullin-3-based E3 ligases.
• Myeloid differentiation primary response 88 (MyD88) is ubiquitylated by SPOP-based E3 ligases, negatively regulating immune signaling, but the precise binding rules are unclear.

Purpose of the Study:

• To elucidate the sequence rules governing SPOP-mediated substrate recognition and degradation.
• To identify novel binding motifs and structural determinants for SPOP-substrate interactions.

Main Methods:

• Biochemical assays to study protein-protein interactions.
• Mammalian cell-based experiments to assess the role of identified motifs.
• X-ray crystallography to determine the structural basis of SPOP-substrate binding.

Main Results:

• MyD88 interacts with SPOP via a long degron containing both a known consensus and a newly identified N-terminal Q-motif.
• Additional substrates, including SRC-3, SETD2, and Caprin1, also engage SPOP through this mechanism.
• The Q-motif is essential for SPOP interactions in mammalian cells, and its structural basis was determined via X-ray crystallography.

Conclusions:

• A new consensus sequence, the Q-motif, expands the known rules for SPOP substrate binding.
• This finding is critical for understanding SPOP-mediated E3 ligase substrate recognition and subsequent ubiquitylation and degradation.