NHLRC4

Model summary

A nucleocytoplasmic adaptor that uses an NHL-repeat beta-propeller scaffold to organize RNA–protein assemblies controlling post-transcriptional gene expression. By concentrating binding interfaces rather than catalytic motifs, it assembles and remodels ribonucleoprotein complexes that repress translation in the cytosol while also influencing pre-mRNA splicing and nuclear export within the nucleoplasm. Its soluble architecture supports shuttling between these compartments to couple nuclear RNA processing with cytoplasmic translational control.

Predicted Gene Ontology terms

1. 01

   I begin with the InterPro architecture.

   The N-terminal two-thirds of the polypeptide (residues 5–122) is covered by IPR011042, a six-bladed beta-propeller, TolB-like homologous superfamily. This fold creates a radially arranged, solvent-exposed platform that typically mediates multivalent macromolecular recognition rather than catalysis. Within this propeller scaffold lie two tandem NHL repeats: IPR001258 (NHL repeat, residues 48–67) and IPR001258 (NHL repeat, residues 89–119). NHL repeats are characteristic blades or segments of beta-propellers that tune sequence-specific binding to RNA and proteins. The ordered arrangement—an NHL-repeat–decorated TolB-like propeller—causes high-affinity, avidity-driven interactions with RNA–protein assemblies and soluble factors, favoring a non-enzymatic adaptor role. This architecture directly supports a molecular function centered on multivalent macromolecular contacts, consistent with GO:0005515 protein binding.

2. 02

   From this binding-centric core, I infer how the protein regulates gene expression post-transcriptionally.

   NHL-propeller scaffolds frequently dock onto translational machinery and RNA granules. Such docking can repress ribosome engagement or promote assembly of inhibitory ribonucleoprotein complexes, providing a mechanistic route to GO:0017148 negative regulation of translation. The same scaffold can also stabilize or remodel ribonucleoprotein assemblies that influence mRNA maturation and export, explaining how it may modulate pre-mRNA splicing and nuclear export while simultaneously tuning cytosolic translation.

3. 03

   Cellular localization follows from this dual operational landscape.

   The soluble beta-propeller lacks transmembrane segments and secretory signals, favoring a cytosolic and nucleoplasmic distribution. Its role in translational repression and mRNP remodeling anchors it in the cytosol (GO:0005829 cytosol), while its influence on splicing and mRNA processing necessitates nucleoplasmic residency (GO:0005654 nucleoplasm). This nucleocytoplasmic shuttling enables the protein to couple nuclear RNA processing with cytoplasmic utilization or repression of mRNA.

4. 04

   Mechanistically, I hypothesize that the NHL-repeat beta-propeller nucleates transient assemblies with RNA-binding proteins and translation factors to gate ribosome access and mRNP fate.

   In the nucleus, it likely associates with spliceosomal adaptors and export receptors to shape pre-mRNA processing and handoff. In the cytosol, it may bind cap-binding or initiation complexes to dampen initiation, and engage granule-associated adaptors to sequester target transcripts. Candidate partners include initiation factors (eIF4E/eIF4G), poly(A)-binding proteins, and granule organizers such as LSM and DDX-family helicases. Together, these interactions would allow the propeller scaffold to coordinate translational repression with broader RNA maturation and export pathways.