In mammalian cells, protein S-palmitoylation is primarily catalyzed by the DHHC family of palmitoyltransferases. These enzymes are multi-pass transmembrane proteins, typically containing 4 to 6 transmembrane domains (TMDs), with their N- and C-termini oriented toward the cytosol. A key characteristic of this family of enzymes is the highly conserved catalytic core between the second and third transmembrane helix. This core contains the catalytic motif aspartate-histidine-histidine-cysteine (DHHC), where cysteine acts as the active nucleophile engaging in auto palmitoylation (Mitchell et al., 2006; Gottlieb and Linder, 2017). Critically, within this DHHC motif, two zinc ions (Zn²⁺) are coordinated to form a folded zinc finger domain. As this zinc-binding property is fundamental to the domain’s stability and function, the protein family is also named ZDHHC proteins (González Montoro et al., 2013). Genomic databases for humans and mice indicate that this family comprises 23 members, including ZDHHC1-ZDHHC9 and ZDHHC11-ZDHHC24, which encode 23 distinct proteins (Elliot Murphy and Banerjee, 2022). Additionally, some family members, such as ZDHHC13 and ZDHHC17, possess an N-terminal ankyrin repeat domain that specifically mediates interactions with substrate proteins (Lemonidis et al., 2014). Furthermore, most ZDHHC proteins are localized to the endoplasmic reticulum and Golgi apparatus, while a subset, including ZDHHC5, ZDHHC20, and ZDHHC21, predominantly reside at the plasma membrane (Rocks et al., 2010). This distinct subcellular localization determines the subset of substrates accessible to each enzyme, thereby spatially regulating protein S-palmitoylation across different cellular compartments.

Currently, ten depalmitoylases have been identified, which are classified into three main families: 1) the acyl protein thioesterase (APT) family, including APT1/LYPLA1 and APT2/LYPLA2, which are primarily cytosolic; 2) the palmitoyl protein thioesterase (PPT) family, comprising PPT1 and PPT2, which are predominantly localized to lysosomes; and 3) the alpha/beta-hydrolase domain-containing (ABHD) family, including ABHD10 (mitochondria), ABHD16A (membranous), and ABHD17A/B/C (plasma membrane) (Shi et al., 2022; Cai et al., 2023; Fan et al., 2023; Wang et al., 2024). All these enzymes belong to the serine hydrolase superfamily. Despite variations in their overall structure, all depalmitoylases contain a conserved α/β-hydrolase fold and a catalytic triad, which enables them to efficiently catalyze depalmitoylation reactions. Notably, in contrast to S-palmitoylation, which relies on consensus sequences like the DHHC motif, no strict sequence specificity has been identified for depalmitoylase substrate recognition so far (Rocks et al., 2010).

S-palmitoylation and depalmitoylation constitute a dynamic, reversible modification that critically regulates cellular adaptation to changing physiological conditions and external stimuli. The immediate donor of the palmitoyl group is Pal-CoA. Pal-CoA is generated through the acyl-CoA synthetases–mediated activation of palmitic acid, which is primarily produced through de novo lipogenesis (Figure 1). This pathway begins with glucose uptake and glycolysis; the generated pyruvate is converted to acetyl-CoA by pyruvate dehydrogenase in mitochondria. After export to the cytosol, acetyl-CoA is carboxylated to malonyl-CoA by acetyl-CoA carboxylase. Then palmitic acid is synthesized by FAS through a series of reactions that sequentially condense acetyl-CoA with malonyl-CoA.

Palmitoyltransferases exploit the resulting Pal-CoA to attach palmitate to target proteins through a two-step mechanism (Figure 2): first, the enzyme undergoes auto-palmitoylation, whereby a cysteine residue in the palmitoyltransferase utilizes Pal-CoA derived from cellular metabolism to form an acyl-enzyme intermediate via a thioester bond, releasing free CoA-SH. In the absence of a substrate protein, the resulting intermediate is inherently unstable and undergoes slow auto-hydrolysis. Second, in the presence of a substrate protein, the palmitoyl group is transferred from the intermediate to a cysteine residue on the substrate, thereby achieving S-palmitoylation of the target protein (Stix et al., 2020).

Depalmitoylation is catalyzed by depalmitoylases via hydrolysis (Figure 2). All these depalmitoylases share a core α/β-hydrolase fold and a catalytic triad. The catalytic triad activates a water molecule, which then nucleophilically attacks the thioester bond linking the palmitic acid to the cysteine residue of the substrate protein. This hydrolysis reaction cleaves the bond, releasing free palmitate and the depalmitoylated protein. Understanding the enzymes and mechanisms of reversible S-palmitoylation is key to explaining how viruses hijack this system and how hosts exploit it for immune defense.

The initial step of viral infection involves efficient attachment to and entry into host cells. Based on the presence or absence of an envelope, viruses are classified as enveloped and non-enveloped. These two types employ distinct entry mechanisms: enveloped viruses typically enter via receptor binding mediated by viral glycoproteins, followed by fusion of the viral envelope with the host cell membrane; non-enveloped viruses, by contrast, usually rely on endocytosis and subsequent penetration of the endosomal membrane.

Viral genome replication-associated proteins are core components of viral replication, responsible for genome replication, transcription, or the assembly of replication complexes. S-palmitoylation of these proteins can anchor the replication complexes to cellular membranes and regulate protein-protein interactions within the replication machinery. For instance, in alphaviruses such as Semliki Forest virus (SFV) and Sindbis virus (SINV), the non-structural protein nsP1 is palmitoylated at cysteine residues in its C-terminal region (Cys418–420 in SFV and Cys420 in SINV). This modification enhances its binding to the plasma membrane, endosomes, and lysosomes, promotes localization to filopodia, and anchors the replication complex to the plasma membrane via an amphipathic helix. This modification is essential for formation and function of the replication complex (Laakkonen et al., 1996; Karo-Astover et al., 2010). Similarly, in Hepatitis C virus (HCV), S-palmitoylation at Cys172 of the core protein strengthens its association with the endoplasmic reticulum (ER) membrane, particularly the ER-adjacent lipid droplets. This modification promotes the assembly of viral particles on the ER membrane and facilitates their release via ER-derived transport and secretory pathways. Additionally, it induces lipid droplet accumulation, thereby maintaining a lipid environment conducive to viral replication. Mutation of Cys172 significantly reduces the formation of nucleocapsid-like particles (NLPs) in yeast cells and impairs viral particle assembly efficiency in Huh7.5 cells (Majeau et al., 2009). The PRRSV nucleocapsid (N) protein is one of the most abundant viral proteins in PRRSV-infected cells, and the formation of its homodimeric structure is essential for viral assembly and infectivity (Chen et al., 2019; Chang et al., 2020; Zheng et al., 2024). S-palmitoylation at the Cys90 residue of the N protein, catalyzed by ZDHHC3, exhibits a dual regulatory function: on the one hand, this modification interferes with the formation of the N protein-Nsp9 protein complex, inhibits viral RNA synthesis and thereby negatively regulates PRRSV replication (Jing et al., 2025); on the other hand, although the Cys90 mutant is capable of genomic replication and subgenomic mRNA transcription, it fails to produce infectious viral particles, confirming the necessity of this modification for viral assembly and maturation (Lee et al., 2005). Notably, this inhibitory effect of ZDHHC3 is counteracted by the APT1, which removes the palmitate group from N protein, thereby restoring N-Nsp9 interaction and promoting viral RNA synthesis. Pharmacological inhibition of APT1 with the small-molecule inhibitor ML348 effectively suppresses PRRSV-2 replication, highlighting the therapeutic potential of targeting depalmitoylation enzymes (Jing et al., 2025). This exemplifies the dynamic, reversible nature of S-palmitoylation in viral replication, where the balance between ZDHHC-mediated palmitoylation and APT1-mediated depalmitoylation determines the functional outcome. Furthermore, in both PRRSV-1 and PRRSV-2, the GP5 and M proteins are palmitoylated at conserved cysteine residues within their cytoplasmic tails near the transmembrane domain. This modification enables the fatty acid chains to interact with the lipid bilayer, driving the clustering of GP5/M heterodimers in cholesterol-enriched microdomains of the Golgi membrane and inducing membrane curvature, thereby promoting virus assembly and budding. Mutation of any or all S-palmitoylation sites significantly reduces virion production, but does not affect the formation of the disulfide-linked GP5-M dimer, ER-to-Golgi transport, or incorporation into virus particles, nor does it impair viral entry. However, these modifications are crucial for viral assembly and budding (Zhang et al., 2017; Zhang et al., 2021).

Viral assembly and release represent the final sequential steps of the viral life cycle, involving the packaging of newly synthesized genomes and structural proteins into mature virions, followed by egress from host cells. S-palmitoylation of viral proteins involved in these processes primarily modulates membrane curvature (e.g., the amphipathic helix of M2 promotes budding), strengthens protein-protein interactions (e.g., S-palmitoylation of coronaviral E protein facilitates virion assembly), and mediates targeting to lipid rafts or specific cellular compartments (e.g., the Golgi apparatus and the plasma membrane). We classify these proteins into two distinct functional categories: structural proteins that focus on assembly and viroporins that serve dual purposes in ion balance and viral release.

To successfully establish infection, viruses employ host protein S-palmitoyltransferases to modify their own proteins or manipulate the S-palmitoylation of host proteins, thereby suppressing the host immune response. The following sections delineate the key strategies viruses have evolved to subvert host immunity through S-palmitoylation.

In summary, S-palmitoylation, which serves as a versatile and often essential post-translational modification, is hijacked by viruses to facilitate multiple stages of their life cycle. From enhancing membrane fusion during entry (e.g., enveloped virus glycoproteins) to anchoring the replication complexes and promoting the assembly and release of viral particles, this reversible modification fine-tunes the function of viral protein function in a spatiotemporally regulated manner. Notably, S-palmitoylation can exert both positive and negative regulatory effects on viral replication, as exemplified by its role in PRRSV N protein. Additionally, viruses exploit this modification to directly undermine host immune surveillance, such as by downregulating MHC-I or inhibiting cGAS-STING signaling. Collectively, these findings underscore S-palmitoylation as a critical interface in virus-host interactions, highlighting its potential as a target for broad-spectrum antiviral interventions. The diverse strategies employed by different virus families are summarized in Table 2, illustrating how this modification is exploited across distinct lifecycle stages—from entry and replication to assembly and immune evasion.

Beyond targeting specific proteins, some viruses possess the capability to reprogram the host’s palmitoyltransferase system to enhance viral fitness. A prime example is SARS-CoV-2. Research has demonstrated that SARS-CoV-2 infection induces a shift in the transcriptional start site of the host ZDHHC20 gene. This shift triggers a switch from the expression of the canonical 42 kDa short isoform (ZDHHC20^short) to a longer protein variant (ZDHHC20^Long), which contains an additional 67-amino-acid extension at its N-terminus. Compared to ZDHHC20^short, the ZDHHC20^Long isoform exhibits greater stability and a longer half-life. Its N-terminal extension harbors a PERW motif, which mediates its retention within the endoplasmic reticulum (ER). Notably, SARS-CoV-2 assembly occurs specifically at the ER-Golgi intermediate compartment (ERGIC). This relocalization allows ZDHHC20^Long to more efficiently palmitoylate the viral Spike protein, thereby enhancing viral infectivity and cell-cell fusion (Mesquita et al., 2023). Notably, this mechanism is not unique to the virus; it exploits an existing host damage-response pathway, as non-viral injuries can also trigger the expression of ZDHHC20^Long (Mesquita et al., 2023). It remains unknown whether ZDHHC20 exerts a similar mechanism in other viruses and whether its regulation exhibits viral specificity.

The cGAS-STING pathway is the primary innate immune signaling cascade for detecting cytosolic exogenous DNA (e.g., from DNA viruses such as HSV-1). S-palmitoylation modulates multiple steps of this pathway to balance antiviral efficacy and immune homeostasis.

The tumor necrosis factor receptor-associated factor 6 (TRAF6)-transforming growth factor-β-activated kinase 1 (TAK1) pathway is critical for activating the NF-κB and MAPK signaling cascades, which regulate the production of proinflammatory cytokines during antiviral immunity. Although ZDHHC11 can mediate S-palmitoylation, its regulation of the TRAF6-TAK1 pathway in response to DNA viruses is independent of this enzymatic activity. Instead, ZDHHC11 functions in a non-catalytic adaptor capacity.

The C-terminal region (amino acids 198-412) of ZDHHC11 binds to the TRAF-C domain of TRAF6, promoting TRAF6 oligomerization (Liu et al., 2021). Enhanced TRAF6 oligomerization significantly increases its E3 ubiquitin ligase activity, facilitating the synthesis of K63-linked polyubiquitin chains. These chains activate TAK1 and the IκB kinase (IKK) complex, leading to activation of NF-κB pathway and transcription of proinflammatory cytokines (e.g., IL-6, TNF-α) (Liu et al., 2021). It is worth noting that this regulatory effect is independent of the palmitoyltransferase activity of ZDHHC11-mutation of its DHHC domain (the catalytic core) does not affect the activation of NF-κB (Liu et al., 2021).

ZDHHC11 KO bone marrow-derived macrophages (BMDMs) and mouse embryonic fibroblasts (MEFs) show reduced NF-κB activation induced by IL-1β, LPS, or HSV-1 (DNA virus), and decreased mRNA levels of downstream proinflammatory cytokines (IL-6, TNF-α). No such effect is observed for RNA viruses (e.g., SeV) (Liu et al., 2021). ZDHHC11 KO mice that are infected with HSV-1 show markedly lower levels of serum IL-6 and weakened antiviral immune responses (Liu et al., 2021).

Interferon-induced transmembrane (IFITM) proteins are evolutionarily conserved broad-spectrum antiviral restriction factors. The vertebrate IFITM family is divided into three subfamilies: immune-related IFITMs (IFITM1, IFITM2, IFITM3, IFITM6, IFITM7), IFITM5, and IFITM10. Among these, only IFITM1, IFITM2, and particularly IFITM3 exhibit antiviral activity (Gómez-Herranz et al., 2023). Notably, S-palmitoylation is one of the key mechanisms regulating the antiviral activities of these three proteins.

In the innate immune defense against viral infections, the retinoic acid-inducible gene I (RIG-I)-like receptor (RLR) signaling pathway serves as a critical mechanism for recognizing RNA viruses and initiating antiviral responses. Upon RNA virus infection, RLRs detect viral nucleic acids and undergo conformational changes. Through their caspase activation and recruitment domains (CARD), they interact with the CARD domain of MAVS, inducing MAVS to form prion-like aggregates (Chen et al., 2021). These aggregates recruit downstream kinases such as TANK-binding kinase 1 (TBK1) and the IκB kinase (IKK) complex, leading to the activation of transcription factors NF-κB and IRF3/7. This cascade ultimately induces the expression of type I interferons (e.g., IFN-β), proinflammatory cytokines, and interferon-stimulated genes (ISGs), establishing an antiviral state in the host (Sharma et al., 2021).

As the central adaptor protein in the RLR pathway, MAVS function is tightly regulated by various post-translational modifications and protein-protein interactions. Recent studies have revealed that S-palmitoylation of MAVS plays a crucial regulatory role in its mediated antiviral immune response. Different members of the ZDHHC family of palmitoyltransferases have been shown to modulate MAVS function through distinct mechanisms, highlighting the complexity and precision of this regulatory layer in antiviral innate immunity.

S-palmitoylation of MAVS is a key regulatory mechanism in the antiviral innate immune response, and its modification sites, catalytic enzymes, and functional effects have been gradually elucidated through multiple studies. Research has confirmed that S-palmitoylation of MAVS can occur at multiple conserved cysteine residues. Among these, C79 is the first identified core site, and its S-palmitoylation is primarily catalyzed by ZDHHC12. This modification is essential for MAVS to form prion-like aggregates and activate the downstream type I interferon (IFN) pathway (Wang et al., 2024). ZDHHC12 interacts with the full-length MAVS and enhances its S-palmitoylation level upon RNA virus infection. The systemic lupus erythematosus-associated MAVS mutant C79F, which lacks this modification site, impairs IFN production and increases host susceptibility to viral infection (Wang et al., 2024).

Another study has demonstrated that MAVS residue C508 (adjacent to its C-terminal transmembrane domain) can be palmitoylated by ZDHHC7. This modification does not affect the mitochondrial localization of MAVS under resting conditions but significantly enhances the stability of MAVS aggregates on the outer mitochondrial membrane during viral infection, promoting IRF3 phosphorylation and IFN secretion (Liu et al., 2024). ZDHHC3 also exhibits weak catalytic activity. Deficiency of ZDHHC7 markedly reduces antiviral immune responses in macrophages and mice, increasing the replication of influenza virus and encephalomyocarditis virus. The C508S mutant forms only dispersed small punctate aggregates upon stimulation and partially detaches from mitochondria, indicating that S-palmitoylation regulates immune signaling by enhancing the membrane-binding capacity and aggregate stability of MAVS (Liu et al., 2024). This study complements the mechanism of C79 site modification, together revealing the fine-tuning of MAVS aggregation by S-palmitoylation at different stages.

Recent research has further identified C46 and C79 of MAVS as S-palmitoylation sites, catalyzed by ZDHHC24. Palmitic acid can promote this modification and the mitochondrial localization and aggregation of MAVS by enhancing the interaction between ZDHHC24 and MAVS (Bu et al., 2024). Deficiency of ZDHHC24 significantly impairs the activation of the TBK1-IRF3 pathway and IFN production induced by RNA viruses, while a high-palmitic acid diet can enhance antiviral immunity in mice in a ZDHHC24-dependent manner (Bu et al., 2024). Additionally, depalmitoylase APT2 can specifically remove S-palmitoylation from MAVS. The inhibitor ML349 significantly enhances the formation of MAVS aggregate and antiviral responses by blocking this process, offering a potential strategy for targeting the regulation of MAVS S-palmitoylation (Bu et al., 2024).

In summary, S-palmitoylation of MAVS at distinct sites (C46, C79, C508) and its coordinated modification by specific ZDHHC family members (ZDHHC7, ZDHHC12, ZDHHC24) regulate its aggregate stability, mitochondrial localization, and downstream signaling activation. This constitutes a critical regulatory network in antiviral innate immunity and provides novel molecular targets for the treatment of related diseases, such as autoimmune disorders and viral infections.

Overall, S-palmitoylation serves as a pivotal regulatory mechanism across multiple arms of the host antiviral innate immune response. Through site-specific modifications catalyzed by distinct ZDHHC enzymes, it governs the membrane association, stability, aggregation, and signaling competency of key immune adaptors and effectors, including STING, MAVS, and IFITMs. While the modification enhances immune activation of pathways such as cGAS-STING and RLR-MAVS, it also fine-tunes the antiviral efficacy of restriction factors like IFITM3. Notably, the regulatory roles of ZDHHC proteins extend beyond catalytic activity, as exemplified by the scaffolding functions of ZDHHC1 and ZDHHC11 in promoting signalosome assembly. These findings underscore a sophisticated layer of post-translational control that enables the host to launch rapid and tailored defenses against viral invasions. Importantly, this host-centric regulation stands in dynamic contrast to the previously described viral hijacking of S-palmitoylation mechanisms, highlighting the constant tug-of-war at the virus-host interface. The reversibility of this modification further implies that the net immune outcome is determined by the balance between palmitoylation and its counterpart—depalmitoylation, which we will discuss in the following section.

Depalmitoylases play a multifaceted role in the replication of viruses, functioning as a double-edged sword that may either promote or hinder the spread of viral entities.

Early in vitro studies by Veit et al. have demonstrated that the depalmitoylase APT1 could remove palmitic acid from the glycoproteins of several enveloped RNA viruses, including the G protein of vesicular stomatitis virus (VSV), the hemagglutinin of influenza viruses, and the E2 glycoprotein of Semliki Forest virus (SFV). Interestingly, APT1 exhibited poor activity toward the SFV E1 glycoprotein, hinting at an early recognition of substrate specificity among viral proteins (Veit and Schmidt, 2001). This differential susceptibility may stem from distinct local conformations or steric hindrance at the cytoplasmic tail-membrane interface of E1, or it may be attributable to the difference in the number of acylation sites (E1 harbors a single site versus four in E2). In contrast to these early in vitro findings, subsequent cellular studies revealed that some viruses actively exploit host depalmitoylases to enhance their replication. For instance, infection with foot-and-mouth disease virus (FMDV) upregulated the expression of the depalmitoylase APT1, and knockdown of APT1 significantly reduced the synthesis and titers of RNA viruses, indicating a pro-viral role (Guo et al., 2015). A more direct mechanism was observed in Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), where APT1-mediated depalmitoylation of the viral nucleocapsid (N) protein reversed the inhibitory effect of ZDHHC3-mediated S-palmitoylation, restoring the interaction between the N protein and Nsp9 and facilitating the synthesis of viral RNA (Jing et al., 2025). The small-molecule inhibitor ML348, which inhibits APT1, significantly diminishes PRRSV replication, highlighting the potential for therapeutic strategies targeting this enzyme (Jing et al., 2025).

Conversely, depalmitoylases can also act as antiviral factors by modifying host proteins required for viral entry. A prime example is the SARS-CoV-2 receptor, angiotensin-converting enzyme 2 (ACE2). Knockdown of APT1 increases the S-palmitoylation of ACE2, leading to enhanced stabilization on the plasma membrane. This elevated surface expression of ACE2 consequently increases cellular susceptibility to SARS-CoV-2 infection. Accordingly, pharmacological inhibition of APT1 with ML348 boosts SARS-CoV-2 infection efficiency (Xie et al., 2021). This presents a scenario where the same depalmitoylase (APT1) can be pro-viral in one context (e.g., PRRSV) and anti-viral in another (e.g., SARS-CoV-2), depending on whether its substrate is a viral or a host protein.

Collectively, these findings reveal that the influence of depalmitoylases on viral replication is not symmetric. They can be hijacked by viruses to promote their own life cycle through the depalmitoylation of viral proteins, or they can serve as innate barriers by modulating the localization and stability of critical host factors like viral receptors. What, then, determines whether a depalmitoylase acts as a proviral facilitator or an antiviral restriction factor? First, substrate identity is paramount: depalmitoylation of viral proteins (e.g., PRRSV N protein) typically benefits viral replication by reversing host ZDHHC-mediated restriction, whereas depalmitoylation of host proteins required for viral entry, such as the SARS-CoV-2 receptor ACE2, limits infection by reducing receptor surface availability. Second, spatiotemporal expression patterns during infection play a critical role; viruses like FMDV actively upregulate APT1 expression early in infection to enhance replication, whereas in other contexts, constitutive depalmitoylase activity may constitutively suppress viral spread. Third, subcellular compartmentalization determines substrate accessibility; depalmitoylases localized to viral replication factories (e.g., ER-derived membranes) likely encounter viral substrates preferentially, while those at the plasma membrane may predominantly target host entry factors. Fourth, the dynamic balance between ZDHHC-mediated palmitoylation and depalmitoylase activity creates a rheostat-like effect; the net palmitoylation status depends on the relative enzymatic activities, which may vary across cell types, metabolic states, or infection stages. Finally, cell-type-specific expression profiles of depalmitoylase isoforms (e.g., neuron-enriched PPT1 versus ubiquitously expressed APT1/LYPLA1) likely dictate tissue tropism and viral pathogenesis. Understanding these determinants will be essential for predicting when pharmacological inhibition versus enhancement of depalmitoylase activity would constitute an effective antiviral strategy.

Beyond their direct roles in modulating viral proteins and host receptors, depalmitoylases also play a critical role in fine-tuning the host innate immune response. This regulatory function ensures a robust yet controlled antiviral defense, thereby preventing immunopathology. The following examples illustrate how depalmitoylation acts as a key regulator of major innate immune signaling pathways.

The mitochondrial antiviral-signaling protein (MAVS) serves as a crucial regulatory component within the RLR pathway, facilitating the production of type I interferon in response to RNA virus detection. Recent research has identified depalmitoylation as a critical negative feedback mechanism for MAVS. The depalmitoylase APT2 specifically removes palmitoyl groups from MAVS via thioester bond hydrolysis. This depalmitoylation compromises the aggregation and mitochondrial localization of MAVS, which are essential for its signal transduction function. Consequently, APT2 activity results in reduced phosphorylation of TBK1 and IRF3, decreased interferon production, and an attenuated antiviral state. The significance of this regulation is underscored by the fact that the APT2 inhibitor ML349 stabilizes palmitoylated MAVS, restoring its activation and significantly enhancing antiviral immunity against viruses like VSV and SeV both in vitro and in vivo (Bu et al., 2024).

Interestingly, depalmitoylases can also utilize non-enzymatic mechanisms to bolster antiviral defense. Conventional dendritic cells type 1 (cDC1), which is a professional antigen-presenting cell vital for initiating adaptive immunity, employs the depalmitoylase PPT1 in a unique manner. In cDC1s, PPT1 is recruited to phagosomes, where it plays a critical role in maintaining an acidic environment required for viral inactivation, presumably by scaffolding and recruiting the V-ATPase proton pump complex. This function may be unrelated to its canonical depalmitoylase activity (Ou et al., 2019). Furthermore, PPT1 expression is under dynamic regulation: it is highly expressed at steady state to sustain this phagosomal antiviral function, but is rapidly downregulated upon cDC1 activation to facilitate antigen retention and cross-presentation, thereby perfectly balancing innate viral clearance with adaptive immune activation (Ou et al., 2019).

In summary, depalmitoylases serve as precise rheostats for innate immunity. Through enzymatic activity, as seen with APT2 fine-tuning MAVS, they prevent excessive immune activation. Additionally, through both enzymatic and non-enzymatic support roles, as demonstrated by PPT1 in cDC1s, they play a crucial role in enhancing the cell’s defenses against viral threats.

Collectively, the studies discussed herein suggest that depalmitoylation is not merely a passive reversal of S−palmitoylation but an active regulatory layer that shapes viral infection and host immunity. Depalmitoylases function as a double−edged sword: they can be co−opted by viruses to promote replication (e.g., APT1 in PRRSV) or act as host restriction factors by modulating critical proteins such as ACE2 or MAVS. Moreover, their roles extend beyond canonical enzymatic activity, as exemplified by PPT1’s non−catalytic scaffolding function in dendritic cells. Despite these advances, only a subset of known depalmitoylases (APT1, APT2, PPT1, ABHD16A) has been firmly linked to virus-host interactions, leaving a vast landscape for future discoveries.