ARHGAP23

Model summary

A cytoplasmic regulator that assembles at membrane-proximal signaling hubs via PDZ- and PH-mediated targeting and then switches off local Rho-family signaling through a catalytic inactivation module. By scaffolding membrane-associated partners and docking to phosphoinositide-rich sites, it spatially restricts Rho-dependent pathways controlling cytoskeleton and trafficking. The soluble nature of its scaffolded architecture places it in the cytosol and frequently in extracellular vesicle pathways, where it fine-tunes small GTPase signaling dynamics.

Predicted Gene Ontology terms

1. 01

   I begin with the domain architecture.

   The N-terminus contains a PDZ module: IPR036034 (PDZ superfamily, residues 19–159) encompasses IPR001478 (PDZ domain, residues 52–155) and the subtype IPR041489 (PDZ domain 6, residues 99–145). PDZ domains create modular scaffolds that bind short C-terminal motifs of membrane and membrane-proximal proteins, positioning signaling enzymes at specific cortical sites. Midway through the sequence sits a pleckstrin homology module: IPR011993 (PH-like domain superfamily, residues 687–832) that resolves into IPR001849 (Pleckstrin homology domain, residues 688–810) and IPR041681 (Pleckstrin homology domain 9, residues 691–803). PH domains bind phosphoinositides and thereby recruit soluble proteins to membrane surfaces and cytosolic interfaces. The C-terminus carries a RhoGAP engine: IPR008936 (Rho GTPase activation protein superfamily, residues 878–1103) that resolves into IPR000198 (Rho GTPase-activating protein domain, residues 905–1097). This catalytic module accelerates GTP hydrolysis on Rho-family small GTPases. The ordered layout—PDZ scaffold → PH membrane-targeting module → RhoGAP catalytic core—creates a targeting-and-execution machine that assembles at membrane-proximal signaling hubs and then switches local Rho signaling off.

2. 02

   This architecture dictates molecular function.

   The presence of the canonical RhoGAP domain (IPR000198 within IPR008936) causes GTPase activator activity by stabilizing the transition state of GTP hydrolysis on Rho-family GTPases, matching GO:0005096 GTPase activator activity. The PDZ and PH modules do not catalyze; they localize and concentrate the enzyme where its substrate resides. Together, these modules ensure efficient and spatially restricted inactivation of Rho signaling nodes.

3. 03

   From function to process, accelerating Rho-family GTP hydrolysis directly tunes actin dynamics, adhesion, and vesicle traffic—hallmarks of small GTPase pathways.

   By turning off Rho signaling locally, the protein modulates downstream cascades and thereby enacts GO:0051056 regulation of small GTPase mediated signal transduction. The PDZ-guided assembly and PH-mediated membrane targeting ensure that this regulation occurs at defined cortical or endomembrane sites.

4. 04

   Cellular placement follows from the soluble modular nature of PDZ and PH domains and the absence of transmembrane segments: the protein operates as a soluble factor in the cytoplasm, consistent with GO:0005829 cytosol and the broader cytoplasmic designation.

   Its participation in membrane-proximal assemblies and trafficking pathways also makes it a likely cargo of intraluminal vesicles, rationalizing recovery in GO:0070062 extracellular exosome fractions.

5. 05

   Mechanistically, the PDZ domain recruits membrane-proximal scaffolds and receptors; the PH domain binds phosphoinositide-enriched patches; and the RhoGAP core quenches nearby Rho-family switches.

   This tri-modular system predicts interactions with Rho-family GTPases (e.g., RHOA, RHOB, RHOC) as direct substrates, with PDZ-ligand membrane proteins and channels that carry PDZ-binding motifs as adaptors, and with phosphoinositide-rich membrane microdomains that concentrate the complex. I therefore hypothesize transient assemblies with cortical actin regulators and endocytic adaptors that collectively tune Rho signaling and membrane trafficking in human cells.