Recombinant Macaca fascicularis Palmitoyltransferase ZDHHC13 (ZDHHC13)

What is ZDHHC13 and what is its primary enzymatic function?

ZDHHC13 is a member of the DHHC-containing palmitoyl acyltransferases (PATs) family of enzymes. Its primary function is to post-translationally add 16-carbon palmitate to proteins through a thioester linkage, a process known as protein palmitoylation . This reversible post-translational modification is critically important for regulating protein localization, stability, and function within cells . The enzymatic palmitoylation activity of ZDHHC13, rather than its protein scaffolding function, is essential for maintaining normal physiological processes, as demonstrated by studies using enzymatically dead DQ-to-AA ZDHHC13 mutants .

How does ZDHHC13 deficiency affect physiological systems?

ZDHHC13 deficiency impacts multiple physiological systems, with pronounced effects observed in the following areas:

• Skeletal system: Mice with Zdhhc13 deficiency develop osteoporosis, showing growth retardation, delayed secondary ossification center formation, disorganized growth plate structure, and reduced bone mineral density .

• Nervous system: Mutant mice display increased sensorimotor gating, anxiety, hypoactivity, and decreased motor coordination at 3 months of age .

• Integumentary system: ZDHHC13-deficient mice exhibit compromised skin barrier permeability, making them susceptible to environmental bacterial infection and inflammatory dermatitis .

These diverse phenotypes underscore ZDHHC13's role as a critical regulator of multiple developmental and physiological processes.

What are the key target substrates of ZDHHC13?

ZDHHC13 has numerous substrate proteins that undergo palmitoylation. Key identified substrates include:

• MT1-MMP (Membrane Type 1-Matrix Metalloproteinase): A direct substrate whose palmitoylation affects subcellular distribution and is associated with VEGF and osteocalcin expression in chondrocytes and osteoblasts .

• Drp1 (Dynamin-related protein 1): Zdhhc13-dependent Drp1 S-palmitoylation enables normal mitochondrial fission-fusion processes, with direct Zdhhc13-Drp1 protein interaction confirmed both in vitro and in vivo .

• Skin barrier proteins: Including loricrin, peptidyl arginine deiminase type III, and transglutaminase 1, whose palmitoylation by ZDHHC13 is critical for protein stability and proper skin barrier development .

• Huntingtin protein (Htt): ZDHHC13 has been linked to Huntington's disease through Zdhhc13-dependent S-palmitoylation of Htt .

Proteomic approaches have identified over 300 candidate proteins that can be classified into four biological categories: immunological disease, skin development and function, dermatological disease, and lipid metabolism .

How does ZDHHC13-dependent palmitoylation affect mitochondrial dynamics?

ZDHHC13-dependent palmitoylation significantly impacts mitochondrial form and function through its action on Drp1, a key regulator of mitochondrial fission. Research has demonstrated that:

• Loss of Zdhhc13 in cortex and cerebellum results in lower levels of Drp1 S-palmitoylation .

• This decreased palmitoylation leads to altered mitochondrial dynamics, affecting the fission-fusion balance essential for mitochondrial health .

• Disrupted mitochondrial dynamics leads to metabolic adaptations, including increased glycolysis, glutaminolysis, and lactic acidosis .

• The abnormal fission-fusion processes result in disrupted mitochondria morphology and distribution .

• These changes ultimately affect mitochondrial ATP output, neurotransmission, and integrity of synaptic structures in the brain .

The direct Zdhhc13-Drp1 protein interaction confirms Drp1 as a substrate of Zdhhc13, establishing a mechanistic link between palmitoylation status and mitochondrial health .

What is the relationship between ZDHHC13 and neurodegenerative disorders?

ZDHHC13 has significant implications for neurological health and neurodegenerative disorders:

• Zdhhc13-deficient mice exhibit behavioral abnormalities similar to those observed in neurodegenerative conditions, including increased anxiety, hypoactivity, and decreased motor coordination .

• Specific connections to Huntington's disease (HD) have been established:

  • Deficiencies in Zdhhc13 have been linked to HD characterized by progressive neuropathology and motor deficits .

  • This connection is supported by the Zdhhc13-dependent S-palmitoylation of Huntingtin protein (Htt) .

  • Both Zdhhc17 and Zdhhc13 are Htt-interacting proteins with dual functions as PATs and as favoring Mg2+ transport .

• The neurological phenotypes appear to be partly mediated through altered mitochondrial dynamics and subsequent neurotransmitter imbalances .

This relationship between ZDHHC13 and neurodegeneration highlights the importance of protein palmitoylation in maintaining neuronal health and function.

How does ZDHHC13 regulate bone homeostasis?

ZDHHC13 regulates bone homeostasis through several interconnected mechanisms:

• MT1-MMP palmitoylation: ZDHHC13 directly palmitoylates MT1-MMP, affecting its subcellular distribution .

• Growth factor signaling: In Zdhhc13 mutant mice with under-palmitoylated MT1-MMP, there is reduced VEGF expression in hypertrophic chondrocytes and decreased osteocalcin at the cartilage-bone interface .

• Developmental timing: ZDHHC13 deficiency results in:

  • Growth retardation and delayed secondary ossification center formation (observed from day 10)

  • Disorganization in growth plate structure (evident at 4 weeks of age)

  • Progressive reduction in bone mineral density (observed via microCT from 4-20 weeks)

These findings establish ZDHHC13 as a novel regulator of postnatal skeletal development and bone mass acquisition, with ZDHHC13-mediated MT1-MMP palmitoylation serving as a key modulator of bone homeostasis .

What techniques are used to assess ZDHHC13-mediated protein palmitoylation?

Several complementary techniques can be employed to study ZDHHC13-mediated protein palmitoylation:

• Acyl-Biotin Exchange (ABE) Assay: This method has been successfully used to detect Zdhhc13-dependent protein S-palmitoylation in cerebella from wild-type and homozygous mutant mice. The assay revealed significant loss of palmitoylated proteins in both cytosolic and mitochondrial membrane fractions of mutant mice .

• Co-immunoprecipitation: This technique has been applied to identify direct substrates of ZDHHC13, such as MT1-MMP, and to confirm direct protein-protein interactions between Zdhhc13 and substrates like Drp1 .

• Quantitative Proteomics: Advanced proteomic approaches have been employed to identify protein molecules whose palmitoylation is tightly controlled by ZDHHC13, leading to the identification of over 300 candidate proteins across multiple biological categories .

• In vitro Palmitoylation Assays: Biochemical assays can confirm the palmitoylation of specific candidates by ZDHHC13, as demonstrated for loricrin, peptidyl arginine deiminase type III, and transglutaminase 1 .

• Protein Stability Assessment: In vivo protein stability analysis can determine whether palmitoylation affects the stability of target proteins, as shown for peptidyl arginine deiminase type III and transglutaminase 1 .

How can researchers effectively study the phenotypic consequences of ZDHHC13 deficiency?

To comprehensively evaluate the phenotypic consequences of ZDHHC13 deficiency, researchers should employ a multi-faceted approach:

• Genetic Models:

  • Spontaneous mutation models (e.g., the luc mouse model with L203X mutation)

  • Knockout models (complete deletion of Zdhhc13)

  • Enzymatically dead knock-in models (e.g., DQ-to-AA ZDHHC13 mutation)

• Behavioral Testing for Neurological Assessment:

  • Motor function and coordination: rotarod testing, footprint analysis

  • Learning and memory: fear conditioning

  • Anxiety-related behavior: open field testing

  • Sensorimotor gating assessment

• Metabolic Analysis:

  • Evaluation of glycolysis and glutaminolysis

  • Assessment of lactic acid production

  • Neurotransmitter level measurement

• Imaging Techniques:

  • MicroCT for bone mineral density monitoring over time (e.g., 4-20 weeks)

  • Immunohistochemical analyses for protein localization and expression (e.g., VEGF in hypertrophic chondrocytes, osteocalcin at the cartilage-bone interface)

  • Mitochondrial morphology and distribution assessment

• Molecular and Biochemical Analyses:

  • Gene expression analysis (e.g., qPCR)

  • Protein palmitoylation assessment (e.g., ABE assay)

  • Subcellular distribution of target proteins

This comprehensive approach allows for a thorough characterization of the diverse phenotypes associated with ZDHHC13 deficiency across multiple physiological systems.

What considerations should be made when using animal models to study ZDHHC13 function?

When designing studies using animal models to investigate ZDHHC13 function, researchers should consider the following important factors:

• Genetic Background Effects:

  • The same mutations in different genetic backgrounds can yield different phenotypes. For example, the Zdhhc13 (Hip14l) KO mice in FVB/N background may show different phenotypic characteristics compared to the luc mice in C57BL/6NJ background .

  • Appropriate backcrossing or the use of littermate controls is essential for accurate phenotypic analysis.

• Age-Dependent Phenotypes:

  • Many ZDHHC13-related phenotypes are age-dependent, with some manifesting early (e.g., skin changes) and others progressively developing over time (e.g., bone density reduction) .

  • Time-course studies are recommended to capture the full spectrum of phenotypic changes.

• Sex-Specific Differences:

  • When applicable, both male and female animals should be included to identify any sex-specific effects of ZDHHC13 deficiency.

• Model Selection:

  • Different models interrupt ZDHHC13 function in distinct ways:

    • Complete knockout models eliminate all protein functions

    • Point mutations may selectively affect enzymatic activity while preserving scaffolding functions

    • Spontaneous mutations may have variable effects depending on the specific alteration

• Control Selection:

  • Include heterozygous animals in addition to wild-type controls to assess gene dosage effects, as some phenotypes may be apparent even with partial ZDHHC13 deficiency .

• Phenotypic Breadth:

  • Given ZDHHC13's diverse roles, comprehensive phenotyping across multiple physiological systems (skeletal, neurological, dermatological, metabolic) is advisable .

• Species Considerations:

  • When extrapolating from mouse models to other species like Macaca fascicularis, consider species-specific differences in ZDHHC13 function and regulation.

  • For studies using recombinant Macaca fascicularis ZDHHC13, species-specific cellular contexts may be important for accurate functional assessment.