TBC1D22A

TBC1D22A is a TBC-domain-containing protein that binds the Golgi adaptor ACBD3 and competes with PI4KB for occupancy of the same ACBD3 region, thereby providing a mutually exclusive regulatory switch for PI4KB recruitment to the Golgi (PMID:23572552). This ACBD3–TBC1D22A interaction is subverted by picornavirus 3A proteins, with kobuvirus 3A disrupting TBC1D22A binding via the ACBD3 GOLD domain (PMID:23572552). Although annotated as a putative Rab33 GAP, TBC1D22A does not replicate the RAB1B-directed GAP activity or ER-to-Golgi trafficking inhibition exhibited by its paralog TBC1D22B, establishing functional divergence between the two paralogs (PMID:40878439).

1. 2013 High

   Identification of TBC1D22A as an ACBD3-binding partner that competes with PI4KB for the same ACBD3 domain established a mutually exclusive regulatory mechanism governing PI4KB recruitment to the Golgi.

   Evidence Affinity purification-mass spectrometry, reciprocal co-immunoprecipitation, and mammalian two-hybrid domain mapping in mammalian cells

   PMID:23572552

   Open questions at the time

   • Direct GAP activity of TBC1D22A toward Rab33 or any other Rab has not been reconstituted in vitro
   • Functional consequences of disrupting TBC1D22A–ACBD3 binding on Golgi PI4P levels have not been measured
   • Structural basis for the mutually exclusive ACBD3 binding by TBC1D22A versus PI4KB is unknown
2. 2013 Medium

   Demonstrating that picornavirus 3A proteins differentially displace TBC1D22A from ACBD3 revealed that viruses exploit this regulatory axis to reorganize Golgi-associated lipid kinase signaling during replication.

   Evidence Mammalian two-hybrid and affinity purification with enteroviral and kobuviral 3A constructs, domain mapping of ACBD3 GOLD domain

   PMID:23572552

   Open questions at the time

   • Effect of TBC1D22A displacement on viral replication efficiency has not been tested directly
   • Whether TBC1D22A displacement is sufficient to enhance PI4KB recruitment in the context of infection is unresolved
3. 2013 Low

   Genetic linkage of a chromosome 22q13.31 locus encompassing TBC1D22A to autosomal recessive GEFS+ in a consanguineous family raised the possibility of a neurological role, but no causative coding variant in TBC1D22A was identified.

   Evidence Genome-wide SNP genotyping, parametric linkage analysis, haplotype reconstruction, and whole-exome sequencing in a Tunisian family

   PMID:24067191

   Open questions at the time

   • No causative mutation in TBC1D22A has been identified; linkage interval contains other genes
   • No functional or expression data connect TBC1D22A to neuronal excitability or seizure phenotypes
   • Finding has not been replicated in independent cohorts
4. 2025 Medium

   Functional comparison of TBC1D22A and TBC1D22B demonstrated that TBC1D22A lacks RAB1B GAP activity and does not inhibit ER-to-Golgi trafficking, establishing that the two paralogs have diverged in substrate specificity and cellular function.

   Evidence RUSH trafficking assay, co-immunoprecipitation proteomics, proximity labeling, RAB1B silencing, GAP-dead mutant analysis in 3D spheroid culture

   PMID:40878439

   Open questions at the time

   • The bona fide Rab substrate of TBC1D22A GAP activity remains unidentified
   • Whether TBC1D22A regulates a trafficking step distinct from ER-to-Golgi transport is untested
   • Negative result based on a single culture system (3D spheroids); other cell types or conditions not explored

• The direct enzymatic GAP activity of TBC1D22A — its Rab substrate specificity and catalytic parameters — has never been reconstituted, leaving its core molecular function unresolved.
• No in vitro GAP assay with purified TBC1D22A and candidate Rab GTPases has been reported
• Loss-of-function phenotype in mammalian cells or animal models has not been characterized
• Physiological context in which TBC1D22A–ACBD3 competition with PI4KB is rate-limiting is unknown