ARMH1

Model summary

A human cytoplasmic scaffold that uses an armadillo-like helical array to mediate multivalent protein binding and promote proteasome assembly. By stabilizing assembly intermediates and coordinating with chaperones and trafficking adaptors, it concentrates proteostasis machinery in the cytoplasm and at lysosome-proximal membranes. This architecture supports efficient core particle formation and integrates proteasome biogenesis with membrane-associated pathways.

Predicted Gene Ontology terms

1. 01

   I begin with the InterPro architecture.

   The sequence is encompassed by IPR041090 (Protein of unknown function DUF5578 family, residues 1–410), which frames the entire polypeptide and suggests a conserved, non-enzymatic scaffold. Within this envelope sit two overlapping helical repeat signatures: IPR011989 (Armadillo-like helical homologous superfamily, residues 72–381) and IPR016024 (Armadillo-type fold homologous superfamily, residues 83–364). Armadillo-type helical repeats form solenoid scaffolds that create extended protein–protein interaction surfaces rather than catalytic centers. The ordered layout—an N-terminal DUF5578 family framework embedding a central armadillo-like core—causally dictates a binding-centric role, favoring assembly and regulation of multiprotein complexes.

2. 02

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

   Armadillo-like folds generate curved helical arrays that capture partner proteins with high avidity and specificity, a hallmark of assembly factors and adaptors. The absence of catalytic motifs and the dominance of repeat scaffolding reinforce that this protein operates through multivalent binding rather than enzymatic chemistry.

3. 03

   This binding-centric scaffold explains its role in proteasome assembly (GO:0043248).

   The proteasome’s core particle requires precise stoichiometric assembly of α and β subunits guided by assembly factors. An armadillo-like platform can nucleate and stabilize transient intermediates, aligning subunits and shielding hydrophobic interfaces until the mature core forms. The DUF5578 family context likely tunes this scaffold for proteasome biogenesis, providing the structural logic that drives efficient core assembly.

4. 04

   Cellular localization follows from function and membrane association.

   The armadillo scaffold is soluble and typically cytoplasmic, consistent with cytoplasm (GO:0005737). Yet its role in proteasome biogenesis and the presence of trafficking/assembly cues point toward endo-lysosomal pathways; the lysosomal membrane (GO:0005765) emerges as a second anchor site where proteasome precursors and assembly factors can be sequestered or recycled. A parsimonious model is that the protein shuttles between cytoplasm and lysosome-proximal membranes, concentrating proteostasis machinery at membrane-associated assembly hubs.

5. 05

   Mechanistically, I hypothesize that the armadillo-like core forms a curved binding platform that recruits proteasome assembly factors and α/β subunits into defined intermediates.

   At cytoplasmic assembly sites and lysosome-adjacent membranes, this scaffold likely coordinates with chaperones and trafficking adaptors to balance proteasome assembly with turnover. Candidate partners include proteasome assembly factors (e.g., POMP and other biogenesis factors), core particle subunits, and lysosomal/endosomal adaptors that transiently tether the assembly platform to membranes. This arrangement enables efficient proteasome assembly while integrating with membrane-associated proteostasis routes.