TRAPPC4

TRAPPC4 Full Name

trafficking protein particle complex 4

TRAPPC4 Introduction

TRAPPC4 is a core subunit of the TRAPP (transport protein particle) complex, a multimeric GEF that activates Rab GTPases controlling ER-to-Golgi and intra-Golgi trafficking. The protein sits in the central TRAPP complex shared by all TRAPP variants and is essential for assembly of the active holo-complex. TRAPPC4 is widely expressed and is required for early secretory pathway function in virtually all eukaryotic cells, with hypomorphic alleles producing cumulative Golgi trafficking defects.

Figure 1. The structure of TRAPPC4.

Core Subunit of TRAPP and Rab GEF Activity
TRAPPC4 forms part of the TRAPPII and TRAPPIII assemblies, which act as GEFs for the Golgi-resident Rabs Ypt31/32 (yeast) and their mammalian counterparts Rab11 and Rab18. Within the complex, TRAPPC4 contributes to the structural core that positions the catalytic subunits and stabilizes the nucleotide-free intermediate during the GEF reaction. Depletion of TRAPPC4 disrupts Golgi morphology, slows secretory cargo exit, and produces aberrant ER-Golgi intermediate compartments, demonstrating that TRAPPC4 is essential for the fidelity of early secretory trafficking.

Neurodevelopmental Disease
Biallelic variants in TRAPPC4 cause a rare neurodevelopmental syndrome featuring microcephaly, epilepsy, spasticity, and progressive cerebral atrophy, with most disease-causing alleles producing destabilized proteins that prevent TRAPPII/III assembly. Patient-derived cells show fragmented Golgi and impaired secretion, and morpholino knockdown of TRAPPC4 in zebrafish recapitulates the microcephaly phenotype, confirming a conserved role for the subunit in neural development. The condition underscores the critical importance of Golgi trafficking for brain growth and points to potential therapeutic avenues involving chaperone-based stabilization of TRAPPC4 mutants.

Alternate Names for TRAPPC4

TRAPPC4; trafficking protein particle complex 4; trafficking protein particle complex subunit 4; PTD009; SBDN; TRS23; TRS23 homolog; hematopoietic stem/progenitor cell protein 172; CGI-104; HSPC172; SYNBINDIN