RSPRY1

Model summary

A cytoplasmic E3 ubiquitin ligase that assembles a recognition-and-catalysis platform to remodel the proteome. An armadillo-type scaffold and a central SPRY module recruit substrates and adaptors, positioning them for ubiquitin transfer by a C-terminal RING catalytic core. This architecture drives formation of K48-linked polyubiquitin chains that target proteins for proteasomal degradation, thereby tuning pathways linked to apoptosis and cytoskeletal dynamics. The enzyme operates predominantly in the soluble cytosolic compartment, where it organizes transient complexes that couple substrate selection to efficient ubiquitin chain assembly.

Predicted Gene Ontology terms

1. 01

   I begin with the domain architecture.

   The N-terminal half contains IPR016024 (Armadillo-type fold, residues 155–323), a solenoid scaffold that mediates avid protein–protein interactions and often positions downstream recognition modules. Immediately following and partially overlapping, the central region is dominated by a SPRY/B30.2 module: IPR043136 (B30.2/SPRY domain superfamily, residues 318–508), IPR001870 (B30.2/SPRY domain, residues 300–483), IPR003877 (SPRY domain, residues 358–482), and IPR035774 (RING finger and SPRY domain-containing protein 1, SPRY domain, residues 359–479). The SPRY fold is a beta-sandwich that confers substrate/adaptor recognition and frequently pairs with catalytic modules to specify ubiquitination targets. The C-terminal region carries the catalytic E3 machinery: IPR013083 (Zinc finger, RING/FYVE/PHD-type superfamily, residues 513–575) and the specific IPR001841 (Zinc finger, RING-type, residues 527–562). A RING domain coordinates zinc to stabilize an E2~Ub thioester and catalyzes ubiquitin transfer. The overall architecture—ARM scaffold → SPRY recognition module → RING catalytic core—is reinforced by IPR045129 (E3 ubiquitin-protein ligase RNF123/RKP/RSPRY1 family, residues 39–526), which ties this arrangement to a defined E3 ligase lineage. The SPRY region also overlaps IPR013320 (Concanavalin A-like lectin/glucanase domain superfamily, residues 319–486), reflecting the beta-sandwich topology of SPRY and providing a structural basis for high-affinity substrate docking.

2. 02

   This ordered layout dictates molecular function.

   The RING-type zinc finger (IPR001841) provides the catalytic platform for ubiquitin transfer, establishing GO:0004842 ubiquitin-protein transferase activity. The ARM and SPRY modules create multivalent binding surfaces that recruit substrates and cofactors, supporting GO:0005515 protein binding. The combination of a recognition SPRY and a catalytic RING causes selective ubiquitination of bound targets.

3. 03

   From function to process, a RING E3 that builds K48-linked chains drives proteasome targeting.

   The presence of a canonical RING and a substrate-specifying SPRY explains GO:0070936 protein K48-linked ubiquitination and situates the enzyme in GO:0043161 proteasome-mediated ubiquitin-dependent protein catabolic process. By promoting turnover of signaling and cytoskeletal regulators, this E3 can tip cell-fate pathways toward cell death; thus its activity aligns with GO:0043065 positive regulation of apoptotic process, consistent with roles in apoptosis and cytoskeletal remodeling.

4. 04

   Cellular location follows from the soluble, modular architecture and lack of transmembrane segments.

   ARM and SPRY modules typically function in the cytoplasm, and E3 assemblies often operate in the soluble fraction. This supports a cytosolic residency consistent with GO:0005829 cytosol and a broader cytoplasmic localization.

5. 05

   Mechanistically, the ARM–SPRY–RING chain suggests a two-step pathway: the SPRY domain captures specific substrates or adaptors, the ARM fold stabilizes the complex and orients it, and the RING domain catalyzes K48-linked chain assembly using cognate E2s.

   Likely partners include E2 conjugating enzymes that support RING E3s (e.g., UBE2D and UBE2N families), proteasome receptors that recognize polyubiquitin, and cytoskeletal or signaling proteins whose turnover modulates apoptosis and motility. I therefore hypothesize transient assemblies with E2s that favor K48 chain formation, with substrate selection mediated by SPRY-driven recognition and execution by the RING catalytic core.