ZDHHC9

ZDHHC9 is a Golgi-localized protein S-acyltransferase (palmitoyltransferase) that catalyzes the palmitoylation of a broad range of substrates, thereby controlling their membrane localization, protein stability, and downstream signaling across neuronal, metabolic, and oncogenic contexts. ZDHHC9 requires its obligate accessory partner GCP16 for proper folding, stability, and enzymatic activity; a conserved C-terminal cysteine motif mediates GCP16 binding, and disease-associated mutations disrupt this complex and impair a two-step catalytic mechanism involving enzyme autopalmitoylation followed by palmitoyl transfer to substrate (PMID:16000296, PMID:24811172, PMID:37035671). Validated substrates include H-Ras/N-Ras, TC10, GLUT1, β-catenin, MBP, Rab3gap1, Bip/GRP78, STRN4, CD38, hnRNPU, LAMTOR1, CD36, PCBP1, STAT1, and KLF5, through which ZDHHC9 regulates processes as diverse as neuronal dendrite outgrowth, inhibitory synapse formation, myelination, glycolysis, mTORC1 activation, Hippo/YAP signaling, ferroptosis suppression, and exocytosis (PMID:31747610, PMID:34620861, PMID:37865665, PMID:37325411, PMID:41031565, PMID:40903842, PMID:41856969). Loss-of-function mutations in ZDHHC9 cause X-linked intellectual disability (XLID), consistent with the neuronal phenotypes of shorter dendrites, reduced inhibitory synapses, altered E/I balance, and seizure-like activity observed in Zdhhc9 knockout mice (PMID:31747610, PMID:24811172).

1. 2005 High

   Establishing that ZDHHC9 is a palmitoyltransferase: the identity and Golgi localization of ZDHHC9 as an enzyme, its substrate specificity for H-Ras/N-Ras, and its obligate dependence on GCP16 for activity and stability were demonstrated, defining the core enzymatic unit.

   Evidence Purified recombinant DHHC9·GCP16 complex tested in in vitro palmitoylation assays with co-IP and subcellular fractionation

   PMID:16000296

   Open questions at the time

   • Catalytic mechanism (autopalmitoylation intermediate) not yet resolved
   • No structural information on the DHHC9·GCP16 complex
   • Substrate repertoire beyond Ras unknown
2. 2014 High

   Resolving the catalytic mechanism: XLID-associated mutations (R148W, P150S) were shown to specifically impair autopalmitoylation, revealing that ZDHHC9 operates via a two-step ping-pong mechanism — enzyme autopalmitoylation followed by transfer to substrate — and providing a biochemical explanation for disease pathogenesis.

   Evidence In vitro autopalmitoylation assay with purified wild-type and mutant ZDHHC9 proteins

   PMID:24811172

   Open questions at the time

   • No crystal structure to explain how mutations impair autopalmitoylation
   • Whether all XLID mutations act through the same mechanism unknown
3. 2019 High

   Linking ZDHHC9 to neuronal circuit function: loss of Zdhhc9 was shown to shorten dendrites (via Ras palmitoylation) and reduce inhibitory synapses (via TC10 palmitoylation), shifting E/I balance and producing seizure-like activity in mice, establishing the neurological basis for XLID.

   Evidence Hippocampal neurons from Zdhhc9 KO mice analyzed by morphometry, electrophysiology (mEPSC/mIPSC), and palmitoylation assays

   PMID:31747610

   Open questions at the time

   • Whether seizure phenotype is cell-autonomous to specific neuron types not resolved
   • No rescue experiment with wild-type ZDHHC9 re-expression reported
4. 2021 High

   Expanding substrates to metabolic regulation: ZDHHC9 was identified as the palmitoyltransferase for GLUT1 at Cys207, establishing that ZDHHC9-mediated palmitoylation controls a transporter's plasma membrane localization, glycolysis, and tumor growth.

   Evidence ZDHHC9 KO, Cys207 mutation, acyl-biotin exchange assay, glycolysis measurement, and in vivo glioblastoma xenograft

   PMID:34620861

   Open questions at the time

   • Whether other DHHC enzymes can compensate for ZDHHC9 on GLUT1 not tested
   • Tissue specificity of ZDHHC9-GLUT1 axis unclear
5. 2023 High

   Demonstrating palmitoylation as a degradation signal and defining the writer-eraser pair: ZDHHC9 palmitoylation of β-catenin promotes its ubiquitination and degradation, while APT1 depalmitoylation stabilizes β-catenin for nuclear translocation, establishing a reversible palmitoylation cycle governing Wnt pathway output in renal fibrosis.

   Evidence In vivo mouse kidney models with ZDHHC9 ablation/overexpression, palmitoylation and ubiquitination assays, nuclear fractionation

   PMID:37865665

   Open questions at the time

   • Whether this writer-eraser pairing applies in other tissue contexts unknown
   • Direct structural basis of palmitoylation-dependent ubiquitination not shown
6. 2023 High

   Structural requirements for the DHHC9-GCP16 partnership were defined: GCP16 prevents DHHC9 aggregation, a C-terminal cysteine motif is essential for GCP16 binding, and XLID mutations reduce stability of the complex, explaining pathogenicity at a protein folding level.

   Evidence Size-exclusion chromatography, in vitro PAT assays, CCM deletion mutagenesis, disease variant stability analysis

   PMID:37035671

   Open questions at the time

   • No high-resolution structure of the DHHC9·GCP16 complex
   • Whether CCM motif mediates GCP16 binding through direct contacts or indirectly unknown
7. 2023 Medium

   ZDHHC9 was shown to regulate cardiac exocytosis: palmitoylation of Rab3gap1 sequesters it from Rab3a, elevating Rab3a-GTP and impairing ANP secretion, revealing a role in cardiomyocyte vesicle trafficking.

   Evidence Acyl-RAC palmitoylation assay, Rab3a-GTP pulldown, ANP secretion assay in cardiomyocytes

   PMID:37325411

   Open questions at the time

   • Single lab study; independent replication needed
   • Whether ZDHHC9 is the sole PAT for Rab3gap1 not determined
8. 2025 Medium

   ZDHHC9 was found to localize to Golgi outposts in oligodendrocyte processes and palmitoylate MBP; Zdhhc9 KO mice show myelin structural defects, establishing a role in CNS myelination distinct from the synaptic phenotype.

   Evidence Live imaging of ZDHHC9 localization in OL processes, palmitoylation assay for MBP, Zdhhc9 KO mouse with electron microscopy of myelin

   PMID:41031565

   Open questions at the time

   • Whether MBP palmitoylation is the primary driver of myelin defects versus other substrates not resolved
   • Functional rescue with wild-type ZDHHC9 in OLs not shown
9. 2025 Medium

   A rapid expansion of validated substrates in cancer contexts — including CD38, hnRNPU, LAMTOR1, CD36, PCBP1, STRN4, STAT1, and KLF5 — revealed that ZDHHC9-mediated palmitoylation controls diverse signaling outputs (mTOR, Hippo/YAP, JNK/ERK, ferroptosis suppression, JAK-STAT, cAMP/PKA) to promote tumor proliferation, migration, and metastasis across multiple cancer types.

   Evidence Acyl-biotin exchange assays with site-directed mutagenesis of palmitoylation sites, co-immunoprecipitation, downstream pathway assays, and in vivo xenograft/metastasis models across multiple studies

   PMID:39002690 PMID:40903842 PMID:41087856 PMID:41419885 PMID:41535416 PMID:41711908 PMID:41856969 PMID:41882103

   Open questions at the time

   • Each substrate identified in a single lab study; independent validation lacking for most
   • Substrate selectivity determinants for ZDHHC9 versus other DHHC enzymes largely unexplored
   • No global palmitoyl-proteomics in ZDHHC9-null cells to define the complete substrate landscape

• Major open questions include: the high-resolution structure of the DHHC9·GCP16 complex, the molecular determinants of substrate selectivity among DHHC family members, a comprehensive palmitoyl-proteome for ZDHHC9, and the relative contribution of individual substrates to XLID neuropathology.
• No crystal or cryo-EM structure available
• No unbiased palmitoyl-proteomics in ZDHHC9 KO cells published
• Relative contribution of individual substrate palmitoylation to XLID phenotype unresolved