TPGS2

Model summary

A soluble cytosolic scaffold that assembles and stabilizes the tubulin polyglutamylase complex. By organizing catalytic and accessory subunits through a Smi1-like binding core, it promotes tubulin glutamylation and thereby tunes microtubule dynamics and trafficking. This cytoskeletal control propagates to phosphorylation networks and dampens cytosolic antiviral signaling, acting as a negative regulator of cGAMP-driven pathways and broader defense responses to virus.

Predicted Gene Ontology terms

1. 01

   I begin with the InterPro architecture.

   The sequence is dominated by IPR039231 (Tubulin polyglutamylase complex subunit 2 family) spanning residues 3–289, which frames the entire polypeptide as a dedicated component of the tubulin polyglutamylase assembly. Nested within this family scaffold is a Knr4/Smi1-like core: IPR037883 (Knr4/Smi1-like domain superfamily, residues 40–199) and its specific instance IPR018958 (Knr4/Smi1-like domain, residues 44–187). This internal Smi1-like fold is a soluble β-rich module frequently used for macromolecular assembly and targeting rather than catalysis. The ordered layout—an N-to-C-terminal TGase2-complex family envelope containing a central Smi1-like binding module—causes the protein to function as a soluble adaptor/scaffold that binds partners and positions the catalytic subunit of the tubulin polyglutamylase complex. Such an architecture dictates a primary molecular role of multivalent protein association, consistent with GO:0005515 protein binding.

2. 02

   From this binding-centric core, I infer the molecular function and its pathway context.

   The TGase2 complex catalyzes post-translational glutamylation on tubulin C-terminal tails, which tunes microtubule stability and trafficking. A non-catalytic subunit with a Knr4/Smi1-like domain is well-suited to recruit and stabilize the catalytic unit and accessory factors, thereby enabling efficient tubulin polyglutamylase chemistry. This adaptor role explains how the protein contributes to protein phosphorylation (GO:0006468) indirectly: by organizing signaling and trafficking hubs that modulate kinase pathways and by coupling cytoskeletal state to phosphorylation cascades. The same scaffolding logic extends to innate immune signaling: cytosolic assemblies that regulate microtubule-based transport and receptor-proximal adaptors can dampen cGAMP/SIRT1/STING signaling. A soluble TGase2-complex scaffold provides a physical means to suppress this axis, aligning with negative regulation of the cGAMP pathway (GO:0039532) and negative regulation of defense response to virus (GO:0050687).

3. 03

   Cellular placement follows from the soluble Smi1-like architecture and the absence of transmembrane or secretion signals.

   The protein operates in the cytoplasm and specifically the cytosol (GO:0005829), where tubulin modification and cytoskeleton-coupled signaling are coordinated. This soluble cytosolic residency is reinforced by the TGase2-complex family signature and the internal Knr4/Smi1-like domain that typically mediates cytosolic assembly.

4. 04

   Mechanistically, I hypothesize that the protein nucleates a cytosolic polyglutamylase assembly that binds and stabilizes the catalytic subunit and accessory factors, thereby promoting tubulin glutamylation and tuning microtubule dynamics.

   By shaping microtubule-based trafficking and receptor-proximal signaling platforms, it attenuates cGAMP/SIRT1/STING and related antiviral pathways and interfaces with phosphorylation networks. Likely interaction partners include the catalytic tubulin polyglutamylase, additional TGase2-complex subunits, tubulin substrates, and innate immune adaptors that reside in cytosolic signaling condensates.