WHAMMP3

Model summary

A soluble human assembly factor that organizes large cytosolic complexes to regulate actin nucleation and membrane remodeling. By using a central scaffolding module, it promotes multivalent protein binding and complex assembly that tune actin dynamics and endomembrane trafficking. It operates primarily in the cytosol with additional nucleoplasmic access, coordinating cytoskeletal and vesicular pathways through transient assemblies that couple membrane-associated GTPases to actin-nucleation machinery.

Predicted Gene Ontology terms

1. 01

   I begin with the InterPro architecture: a single annotated module, IPR031738 (JMY/WHAMM, middle domain, residues 37–152).

   In JMY/WHAMM-family proteins, the middle domain forms a helical scaffold that mediates multivalent protein–protein interactions and oligomerization. Its position near the N- to mid-region creates an assembly hub that recruits partners and couples membrane-associated GTPases to actin nucleation machinery. This architecture inherently promotes protein binding rather than catalysis, aligning with GO:0005515 protein binding as the primary molecular function.

2. 02

   A central scaffold of this kind drives higher-order assembly of large cytosolic complexes.

   By stabilizing and organizing multi-subunit assemblies, the middle domain directly causes GO:0065003 protein-containing complex assembly. In the JMY/WHAMM lineage, this assembly role extends to actin nucleation and membrane remodeling: the scaffold nucleates complexes that activate Arp2/3-mediated actin polymerization and coordinate membrane tubulation. Such coordinated assembly explains how the protein can both regulate actin dynamics and influence endomembrane trafficking.

3. 03

   The absence of transmembrane segments and the presence of a soluble assembly platform indicate a cytosolic residency.

   This supports GO:0005829 cytosol and is consistent with a broader cytoplasmic distribution. The reported nucleoplasmic presence (GO:0005654 nucleoplasm) suggests regulated nucleocytoplasmic shuttling—likely a means to couple cytoskeletal and membrane-remodeling programs to nuclear signaling or transcriptional control. Together, these localizations fit a soluble factor that operates predominantly in the cytosol with transient nuclear access.

4. 04

   Mechanistically, the middle-domain scaffold recruits and positions partners that together control actin nucleation and membrane dynamics.

   By concentrating GTPase effectors and nucleators, it can bias Arp2/3 activity and membrane tubulation, thereby tuning both cytoskeletal remodeling and endomembrane trafficking. I hypothesize that it transiently associates with small GTPases and their effectors, clathrin/adaptor assemblies, and actin-nucleation modules. These interactions would allow it to bridge membrane-bound cargo selection with cytoskeletal forces, explaining its dual role in actin regulation and vesicle pathway control.