ASB15

Model summary

A cytosolic ankyrin-repeat scaffold that captures specific protein substrates and recruits an Elongin–Cullin–RING ubiquitination module via its SOCS box. By coupling high-specificity substrate recognition to assembly of ubiquitin-transfer machinery, it promotes substrate polyubiquitination and subsequent proteasome-directed turnover, thereby shaping cytosolic proteostasis and signaling pathways.

Predicted Gene Ontology terms

1. 01

   I begin with the domain architecture.

   The N-terminal two-thirds of the protein is dominated by IPR036770 (Ankyrin repeat-containing domain superfamily, residues 39–446), within which lie multiple specific ankyrin-repeat modules: IPR002110 Ankyrin repeat units at residues 110–208, 209–241, 242–339, and 344–409. Ankyrin repeats form elongated solenoid scaffolds that create high-affinity, sequence-specific protein-binding grooves; this architecture causes selective recognition and stable capture of target proteins. The C-terminal region contains IPR036036 (SOCS box-like domain superfamily, residues 524–579) and the embedded IPR001496 SOCS box domain (residues 528–579). The SOCS box is a hallmark recruitment module that binds Elongin B/C and couples to Cullin–RING ligase cores. The ordered layout—ankyrin-repeat substrate-binding platform followed by a SOCS-box adaptor—establishes a canonical ankyrin/SOCS architecture that drives substrate recognition and ubiquitin pathway assembly.

2. 02

   From this architecture, the molecular function resolves as protein binding (GO:0005515).

   The ankyrin array supplies the avid, modular binding surface that selects substrates, while the SOCS box recruits the ubiquitination machinery. This coupling of recognition and assembly directly drives protein ubiquitination (GO:0016567). Once assembled with Elongin B/C and a Cullin–RING core, the complex catalyzes ubiquitin transfer to bound substrates, committing them to the ubiquitin-dependent protein catabolic process (GO:0006511). Thus, the ankyrin repeats cause substrate capture, and the SOCS box causes ubiquitin-system engagement; together they enforce ubiquitin-mediated proteostasis.

3. 03

   Cellular localization follows from function and composition.

   The absence of transmembrane segments and the soluble nature of ankyrin/SOCS assemblies point to a cytosolic environment where CRL assembly and substrate turnover are most active. This supports a cytosolic localization (GO:0005829 cytosol), consistent with soluble adaptor-driven ubiquitination hubs that patrol the cytoplasm.

4. 04

   Mechanistically, the protein likely operates as a substrate adaptor within a CRL complex.

   The ankyrin repeats bind specific targets—potentially including regulatory factors—while the SOCS box recruits Elongin B/C and engages a Cullin–RING scaffold to catalyze polyubiquitin chain formation and subsequent proteasomal degradation. I therefore hypothesize interactions with Elongin B and C, Cullin family components (e.g., CUL5 commonly paired with SOCS boxes), and RING-box proteins, forming a dynamic ubiquitination assembly that tunes cytosolic protein stability and signaling thresholds.