SPRY domain in Fbxo45 and suppressors of cytokine signaling (SOCS) proteins
This family consists of the SPRY domain-containing SOCS box protein family (SPSB1-4, also known as SSB-1 to -4) as well as F-box protein 45 (Fbxo45), a novel synaptic E3 and ubiquitin ligase. The SPSB protein is composed of a central SPRY protein interaction domain and a C-terminal SOCS box. SPSB1, SPSB2, and SPSB4 interact with prostate apoptosis response protein 4 (Par-4) and are negative regulators that recruit the ECS E3 ubiquitin ligase complex to polyubiquitinate inducible nitric-oxide synthase (iNOS), resulting in its proteasomal degradation. Fbxo45 is related to this family; it is located N-terminal to the SPRY domain, and known to induce the degradation of a synaptic vesicle-priming factor, Munc13-1, via the SPRY domain, thus playing an important role in the regulation of neurotransmission by modulating Munc13-1 at the synapse. Suppressor of cytokine signaling (SOCS) proteins negatively regulate signaling from JAK-associated cytokine receptor complexes, and play key roles in the regulation of immune homeostasis.
Jiyao W et al.(2023). "The conserved domain database in 2023.",