PKM2 induces mitophagy through the AMPK-mTOR pathway promoting CSFV proliferation.

Viruses exploit the host cell's energy metabolism system to support their replication. Mitochondria, known as the powerhouse of the cell, play a critical role in regulating cell survival and virus replication. Our prior research indicated that the classical swine fever virus (CSFV) alters mitochondrial dynamics and triggers glycolytic metabolic reprogramming. However, the role and mechanism of PKM2, a key regulatory enzyme of glycolytic metabolism, in CSFV replication remain unclear. In this study, we discovered that CSFV enhances PKM2 expression and utilizes PKM2 to inhibit pyruvate production. Using an affinity purification coupled mass spectrometry system, we successfully identified PKM as a novel interaction partner of the CSFV non-structural protein NS4A. Furthermore, we validated the interaction between PKM2 and both CSFV NS4A and NS5A through co-immunoprecipitation and confocal analysis. PKM2 was found to promote the expression of both NS4A and NS5A. Moreover, we observed that PKM2 induces mitophagy by activating the AMPK-mTOR signaling pathway, thereby facilitating CSFV proliferation. In summary, our data reveal a novel mechanism whereby PKM2, a metabolic enzyme, promotes CSFV proliferation by inducing mitophagy. These findings offer a new avenue for developing antiviral strategies. IMPORTANCE: Viruses rely on the host cell's material-energy metabolic system for replication, inducing host metabolic disorders and subsequent immunosuppression-a major contributor to persistent viral infections. Classical swine fever virus (CSFV) is no exception. Classical swine fever is a severe acute infectious disease caused by CSFV, resulting in significant economic losses to the global pig industry. While the role of the metabolic enzyme PKM2 (pyruvate dehydrogenase) in the glycolytic pathway of tumor cells has been extensively studied, its involvement in viral infection remains relatively unknown. Our data unveil a new mechanism by which the metabolic enzyme PKM2 mediates CSFV infection, offering novel avenues for the development of antiviral strategies.

The role of PKM2 in cancer progression and its structural and biological basis.

Pyruvate kinase M2 (PKM2), a subtype of pyruvate kinase (PK), has been shown to play an important role in the development of cancer. It regulates the last step of glycolytic pathway. PKM2 has both pyruvate kinase and protein kinase activity, and the conversion of these two functions of PKM2 depends on the mutual change of dimer and tetramer. The dimerization of PKM2 can promote the proliferation and growth of tumor cells, so inhibiting the dimerization of PKM2 is essential to curing cancer. The aggregation of PKM2 is regulated by both endogenous and exogenous cofactors as well as post-translational modification (PTM). Although there are many studies on the different aggregation of PKM2 in the process of tumor development, there are few summaries in recent years. In this review, we first introduce the role of PKM2 in various biological processes of tumor growth. Then, we summarize the aggregation regulation mechanism of PKM2 by various endogenous cofactors such as Fructose-1, 6-diphosphate (FBP), various amino acids, and post-translational modification (PTMs). Finally, the related inhibitors and agonists of PKM2 are summarized to provide reference for regulating PKM2 aggregation in the treatment of cancer in the future.

PYK-SubstitutionOME: an integrated database containing allosteric coupling, ligand affinity and mutational, structural, pathological, bioinformatic and computational information about pyruvate kinase isozymes.

Interpreting changes in patient genomes, understanding how viruses evolve and engineering novel protein function all depend on accurately predicting the functional outcomes that arise from amino acid substitutions. To that end, the development of first-generation prediction algorithms was guided by historic experimental datasets. However, these datasets were heavily biased toward substitutions at positions that have not changed much throughout evolution (i.e. conserved). Although newer datasets include substitutions at positions that span a range of evolutionary conservation scores, these data are largely derived from assays that agglomerate multiple aspects of function. To facilitate predictions from the foundational chemical properties of proteins, large substitution databases with biochemical characterizations of function are needed. We report here a database derived from mutational, biochemical, bioinformatic, structural, pathological and computational studies of a highly studied protein family-pyruvate kinase (PYK). A centerpiece of this database is the biochemical characterization-including quantitative evaluation of allosteric regulation-of the changes that accompany substitutions at positions that sample the full conservation range observed in the PYK family. We have used these data to facilitate critical advances in the foundational studies of allosteric regulation and protein evolution and as rigorous benchmarks for testing protein predictions. We trust that the collected dataset will be useful for the broader scientific community in the further development of prediction algorithms. Database URL https://github.com/djparente/PYK-DB.

Roadmap to Pyruvate Kinase M2 Modulation - A Computational Chronicle.

Pyruvate kinase M2 (PKM2) has surfaced as a potential target for anti-cancer therapy. PKM2 is known to be overexpressed in the tumor cells and is a critical metabolic conduit in supplying the augmented bioenergetic demands of the recalcitrant cancer cells. The presence of PKM2 in structurally diverse tetrameric as well as dimeric forms has opened new avenues to design novel modulators. It is also a truism to state that drug discovery has advanced significantly from various computational techniques like molecular docking, virtual screening, molecular dynamics, and pharmacophore mapping. The present review focuses on the role of computational tools in exploring novel modulators of PKM2. The structural features of various isoforms of PKM2 have been discussed along with reported modulators. An extensive analysis of the structure-based and ligand- based in silico methods aimed at PKM2 modulation has been conducted with an in-depth review of the literature. The role of advanced tools like QSAR and quantum mechanics has been established with a brief discussion of future perspectives.

Identification of residues involved in allosteric signal transmission from amino acid binding site of pyruvate kinase muscle isoform 2.

PKM2 is a rate-limiting enzyme in the glycolytic process and is involved in regulating tumor proliferation. Several amino acids (AAs) such as Asn, Asp, Val, and Cys have been shown to bind to the AA binding pocket of PKM2 and modulate its oligomeric state, substrate binding affinity, and activity. Although previous studies have attributed that the main chain and side chain of bound AAs are responsible for initiating signal to regulate PKM2, the signal transduction pathway remains elusive. To identify the residues involved in signal transfer process, N70 and N75 located at two ends of a ß strand connecting the active site and AA binding pocket were altered. Biochemical studies of these variants with various AA ligands (Asn, Asp, Val, and Cys), illustrate that N70 and N75, along with ß1 connecting these residues are part of the signal transduction pathway between the AA binding pocket and the active site. The results demonstrate that mutation of N70 to D prevents the transfer of the inhibitory signal mediated by Val and Cys, whereas N75 to L alteration blocks the activating signal initiated by Asn and Asp. Taken together, this study confirms that N70 is one of the residues responsible for transmitting the inhibitory signal and N75 is involved in the activation signal flow.

Serendipitous Identification of a Covalent Activator of Liver Pyruvate Kinase.

Enzymes are effective biological catalysts that accelerate almost all metabolic reactions in living organisms. Synthetic modulators of enzymes are useful tools for the study of enzymatic reactions and can provide starting points for the design of new drugs. Here, we report on the discovery of a class of biologically active compounds that covalently modifies lysine residues in human liver pyruvate kinase (PKL), leading to allosteric activation of the enzyme (EC50 =0.29 µM). Surprisingly, the allosteric activation control point resides on the lysine residue K282 present in the catalytic site of PKL. These findings were confirmed by structural data, MS/MS experiments, and molecular modelling studies. Altogether, our study provides a molecular basis for the activation mechanism and establishes a framework for further development of human liver pyruvate kinase covalent activators.

Identification of Natural Compounds as Inhibitors of Pyruvate Kinase M2 for Cancer Treatment.

The reliance of tumor cells on aerobic glycolysis is one of the emerging hallmarks of cancer. Pyruvate kinase M2 (PKM2), an important enzyme of glycolytic pathway, is highly expressed in a number of cancer cells. Tumor cells heavily depend on PKM2 to fulfill their divergent energetic and biosynthetic requirements, suggesting it as novel drug target for cancer therapies. Based on this context, we performed enzymatic-assay-based screening of the in-house phenolic compounds library for the identification of PKM2 inhibitors. This screening identified silibinin, curcumin, resveratrol, and ellagic acid as potential inhibitors of PKM2 with IC50 values of 0.91 µM, 1.12 µM, 3.07 µM, and 4.20 µM respectively. For the determination of Ki constants and the inhibition type of hit compounds, Lineweaver-Burk graphs were plotted. Silibinin and ellagic acid performed the competitive inhibition of PKM2 with Ki constants of 0.61 µM and 5.06 µM, while curcumin and resveratrol were identified as non-competitive inhibitors of PKM2 with Ki constants of 1.20 µM and 7.34 µM. The in silico screening of phenolic compounds against three binding sites of PKM2 provided insight into the binding pattern and functionally important amino residues of PKM2. Further, the evaluation of cytotoxicity via MTT assay demonstrated ellagic acid as potent inhibitor of cancer cell growth (IC50 = 20 µM). These results present ellagic acid, silibinin, curcumin, and resveratrol as inhibitors of PKM2 to interrogate metabolic reprogramming in cancer cells. This study has also provided the foundation for further research to validate the potential of identified bioactive entities for PKM2 targeted-cancer therapies.

Odd one out? Functional tuning of Zymomonas mobilis pyruvate kinase is narrower than its allosteric, human counterpart.

Various protein properties are often illuminated using sequence comparisons of protein homologs. For example, in analyses of the pyruvate kinase multiple sequence alignment, the set of positions that changed during speciation ("phylogenetic" positions) were enriched for "rheostat" positions in human liver pyruvate kinase (hLPYK). (Rheostat positions are those which, when substituted with various amino acids, yield a range of functional outcomes). However, the correlation was moderate, which could result from multiple biophysical constraints acting on the same position during evolution and/or various sources of noise. To further examine this correlation, we here tested Zymomonas mobilis PYK (ZmPYK), which has <65% sequence identity to any other PYK sequence. Twenty-six ZmPYK positions were selected based on their phylogenetic scores, substituted with multiple amino acids, and assessed for changes in Kapp-PEP . Although we expected to identify multiple, strong rheostat positions, only one moderate rheostat position was detected. Instead, nearly half of the 271 ZmPYK variants were inactive and most others showed near wild-type function. Indeed, for the active ZmPYK variants, the total range of Kapp,PEP values ("tunability") was 40-fold less than that observed for hLPYK variants. The combined functional studies and sequence comparisons suggest that ZmPYK has evolved functional and/or structural attributes that differ from the rest of the family. We hypothesize that including such "orphan" sequences in MSA analyses obscures the correlations used to predict rheostat positions. Finally, results raise the intriguing biophysical question as to how the same protein fold can support rheostat positions in one homolog but not another.

A magneto-controlled biocatalytic cascade with a fluorescent output.

A biocatalytic cascade based on concerted operation of pyruvate kinase and luciferase with a bioluminescent output was switched reversibly between low and high activity by applying an external magnetic field at different positions or removing it. The enzymes participating in the reaction cascade were bound to magnetic nanoparticles to allow their translocation or aggregation/dispersion to be controlled by the magnetic field. The reaction intensity, measured as the bioluminescent output, was dependent on the effective distances between the enzymes transported on the magnetic nanoparticles controlled by the magnets.

Reversible amyloids of pyruvate kinase couple cell metabolism and stress granule disassembly.

Cells respond to stress by blocking translation, rewiring metabolism and forming transient messenger ribonucleoprotein assemblies called stress granules (SGs). After stress release, re-establishing homeostasis and disassembling SGs requires ATP-consuming processes. However, the molecular mechanisms whereby cells restore ATP production and disassemble SGs after stress remain poorly understood. Here we show that upon stress, the ATP-producing enzyme Cdc19 forms inactive amyloids, and that their rapid re-solubilization is essential to restore ATP production and disassemble SGs in glucose-containing media. Cdc19 re-solubilization is initiated by the glycolytic metabolite fructose-1,6-bisphosphate, which directly binds Cdc19 amyloids, allowing Hsp104 and Ssa2 chaperone recruitment and aggregate re-solubilization. Fructose-1,6-bisphosphate then promotes Cdc19 tetramerization, which boosts its activity to further enhance ATP production and SG disassembly. Together, these results describe a molecular mechanism that is critical for stress recovery and directly couples cellular metabolism with SG dynamics via the regulation of reversible Cdc19 amyloids.

In Silico Study of the Structure and Ligand Preference of Pyruvate Kinases from Cyanobacterium Synechocystis sp. PCC 6803.

Finding reliable cheap sources for producing chemicals and materials is always challenging. During recent decades, photosynthetic organisms such as cyanobacteria, which used CO2 as a carbon source for making products, have attracted a great deal of attention. Among cyanobacteria, Synechocystis sp. PCC 6803 has been considered as a model strain and has some desirable features that make it suitable for use as an industrial strain. Pyruvate kinase (PK) catalyzes the transformation of phosphoenolpyruvate (PEP) to pyruvate in the last step of glycolysis that is an essential enzyme to produce adenosine triphosphate (ATP) in all organisms. Therefore, it plays a critical role in regulating cell metabolism. However, active and allosteric sites of PK and allosteric mechanisms governing PK activity are poorly understood in many bacteria. This study was aimed to provide more insight into PKs of Synechocystis sp. PCC 6803, using in silico methods. The results indicated that predicted structures of PKs from Synechocystis sp. PCC 6803 are reliable and can be considered for further studies. Molecular docking studies suggested that for predicted structures of sll0587 and sll1275, respectively, there are three and two possible active or allosteric sites. Furthermore, molecular interaction analysis of modeled structures proposes that sll0587 is strongly inhibited by ATP and when ATP concentration is low, this isoenzyme is active.

Rheostat functional outcomes occur when substitutions are introduced at nonconserved positions that diverge with speciation.

When amino acids vary during evolution, the outcome can be functionally neutral or biologically-important. We previously found that substituting a subset of nonconserved positions, "rheostat" positions, can have surprising effects on protein function. Since changes at rheostat positions can facilitate functional evolution or cause disease, more examples are needed to understand their unique biophysical characteristics. Here, we explored whether "phylogenetic" patterns of change in multiple sequence alignments (such as positions with subfamily specific conservation) predict the locations of functional rheostat positions. To that end, we experimentally tested eight phylogenetic positions in human liver pyruvate kinase (hLPYK), using 10-15 substitutions per position and biochemical assays that yielded five functional parameters. Five positions were strongly rheostatic and three were non-neutral. To test the corollary that positions with low phylogenetic scores were not rheostat positions, we combined these phylogenetic positions with previously-identified hLPYK rheostat, "toggle" (most substitution abolished function), and "neutral" (all substitutions were like wild-type) positions. Despite representing 428 variants, this set of 33 positions was poorly statistically powered. Thus, we turned to the in vivo phenotypic dataset for E. coli lactose repressor protein (LacI), which comprised 12-13 substitutions at 329 positions and could be used to identify rheostat, toggle, and neutral positions. Combined hLPYK and LacI results show that positions with strong phylogenetic patterns of change are more likely to exhibit rheostat substitution outcomes than neutral or toggle outcomes. Furthermore, phylogenetic patterns were more successful at identifying rheostat positions than were co-evolutionary or eigenvector centrality measures of evolutionary change.

Synthesis, Molecular Docking Studies and Antibacterial Activities of Novel Monocationic Indole-benzimidazole Derivatives.

BACKGROUND: Finding efficient therapy against hospital-acquired MRSA infections has become rather important in the last decade. To this end, inhibition of the enzyme pyruvate kinase (PK) is being investigated for antibacterial activity, since this enzyme controls energy generation and metabolic flux distribution. Our main scaffold consists of benzimidazole and indole rings fused together. Both rings are famous for antibacterial properties and promising anti-MRSA compounds including indole ring. METHODS: Several 1-substituted-2-(1H-indol-3-yl)-N-substituted-1H-benzimidazole-5-carboxamidine analogues were developed, synthesized and their antibacterial activities were evaluated against Staphylococcus aureus (ATCC 25923), Methicillin resistant Staphylococcus aureus (MRSA) (ATCC 43300), and Staphylococcus epidermidis (ATCC 12228) by using tube dilution method. Molecular docking analysis with a characteristic protein called MRSA- Pyruvate Kinase has been conducted for the assessment of the activities of our compounds against Methicillinresistant S. aureus (MRSA). RESULTS: Among all the tested compounds, the most potent compound 36 had MIC values as 3.12, 3.12 and 6.25 µg/mL against S. aureus, Methicillin-resistant S. aureus (MRSA), and S. epidermidis, respectively. This compound had much better docking energy value than standard ampicillin and also created the link between two residues in different monomers of PK. DISCUSSION: This approach of using indol-amidine conjugate systems as anti-MRSA agents may include MRSA-PK as potential target. To further increase the affinity, some other H-bonding parts may be added. By doing so, another bridge with Ile361 residues on both sides can be created. Our compounds tend to violate log P limit of Lipinski, therefore some optimizations with formulation can be made. CONCLUSION: This study mainly includes the design, synthesis and optimization of indolebenzimidazole- amidine derivatives. Docking studies confirmed our results, since our most potent hit compound 36 created the necessary interactions between two chains of MRSA-PK. Further optimization can be considered to increase drug ability.

Regulation of an important glycolytic enzyme, pyruvate kinase, through phosphorylation in the larvae of a species of freeze-tolerant insect, Eurosta solidaginis.

Larvae of the goldenrod gall fly, Eurosta solidaginis, rely on a freeze tolerance strategy to survive the sub-zero temperatures of Canadian winter. Critical to their survival is the accumulation of polyol cryoprotectants and global metabolic rate depression, both of which require the regulation of glycolysis and reorganization of carbohydrate metabolism. This study explored the role that pyruvate kinase (PK) regulation plays in this metabolic reorganization. PK was purified from control (5 °C-acclimated) and frozen (-15 °C-acclimated) larvae and enzyme kinetic properties, structural stability, and post-translational modifications were examined in both enzyme forms. The Km phosphoenolpyruvate (PEP) of frozen PK was 20% higher than that of control PK, whereas the Vmax of frozen PK was up to 50% lower than that of control PK at the lowest assay temperature, suggesting inhibition of the enzyme during the winter. Additionally, the activity and substrate affinity of both forms of PK decreased significantly at low assay temperatures, and both forms were regulated allosterically by a number of metabolites. Pro-Q™ Diamond phosphoprotein staining and immunoblotting experiments demonstrated significantly higher threonine phosphorylation of PK from frozen animals while acetylation and methylation levels remained constant. Together, these results indicate that PK exists in two structurally distinct forms in E. solidaginis. In response to conditions mimicking the transition to winter, PK appears to be regulated to support metabolic rate depression, the accumulation of polyol cryoprotectants, and the need for extended periods of anaerobic carbohydrate metabolism to allow the animal to survive whole-body freezing.

Purification and Regulation of Pyruvate Kinase from the Foot Muscle of the Anoxia and Freeze Tolerant Marine Snail, Littorina littorea.

The intertidal marine snail, Littorina littorea, has evolved to survive bouts of anoxia and extracellular freezing brought about by changing tides and subsequent exposure to harsh environmental conditions. Survival in these anoxic conditions depends on the animals entering a state of metabolic rate depression in order to maintain an appropriate energy production-consumption balance during periods of limited oxygen availability. This study investigated the kinetic, physical, and regulatory properties of pyruvate kinase (PK), which catalyzes the final reaction of aerobic glycolysis, from foot muscle of L. littorea to determine if the enzyme is differentially regulated in response to anoxia and freezing exposure. PK purified from foot muscle of anoxic animals exhibited a lower affinity for its substrate phosphoenolpyruvate than PK from control and frozen animals. PK from anoxic animals was also more sensitive to a number of allosteric regulators, including alanine and aspartate, which are key anaerobic metabolites in L. littorea. Furthermore, PK purified from anoxic and frozen animals exhibited greater stability compared to the non-stressed control animals, determined through high-temperature incubation studies. Phosphorylation of threonine and tyrosine residues was also assessed and demonstrated that levels of threonine phosphorylation of PK from anoxic animals were significantly higher than those of PK from control and frozen animals, suggesting a potential mechanism for regulating PK activity. Taken together, these results suggest that PK plays a role in suppressing metabolic rate in these animals during environmental anoxia exposure.

The phosphate moiety of phosphoenolpyruvate does NOT contribute to allosteric regulation of liver pyruvate kinase by fructose-1,6-bisphosphate✝.

A linked-function theory for allostery allows for a differentiation between those protein-ligand interactions that contribute the most to ligand binding and those protein-ligand interactions that contribute to the allosteric mechanism. This potential distinction is the basis for analogue studies used to determine which chemical moieties on the allosteric effector contribute to allostery. Although less recognized, the same separation of functions is possible for substrate-enzyme interactions. When evaluating allosteric regulation in human liver pyruvate kinase, the use of a range of monovalent cations (K+, NH4+, Rb+, Cs+, cyclohexylammonium+ and Tris+) altered substrate (phosphoenolpyruvate; PEP) affinity, but maintained similar allosteric responses to the allosteric activator, fructose-1,6-bisphosphate (Fru-1,6-BP). Because crystal structures indicate that the active site monovalent cation interacts directly with the phosphate moiety of the bound PEP substrate, we questioned if the phosphate moiety might contribute to substrate binding, but not to the allosteric mechanism. Here, we demonstrate that the binding of oxalate, a non-phosphorylated substrate/product analogue, is allosterically enhanced by Fru-1,6-BP. That observation is consistent with the concept that the phosphate moiety of PEP is not required for the allosteric function, even though that moiety likely contributes to determining substrate affinity.

Pyruvate kinase from Plasmodium falciparum: Structural and kinetic insights into the allosteric mechanism.

During its intra-erythrocytic growth phase, the malaria parasite Plasmodium falciparum relies heavily on glycolysis for its energy requirements. Pyruvate kinase (PYK) is essential for regulating glycolytic flux and for ATP production, yet the allosteric mechanism of P. falciparum PYK (PfPYK) remains poorly understood. Here we report the first crystal structure of PfPYK in complex with substrate analogues oxalate and the ATP product. Comparisons of PfPYK structures in the active R-state and inactive T-state reveal a 'rock-and-lock' allosteric mechanism regulated by rigid-body rotations of each subunit in the tetramer. Kinetic data and structural analysis indicate glucose 6-phosphate is an activator by increasing the apparent maximal velocity of the enzyme. Intriguingly, the trypanosome drug suramin inhibits PfPYK, which points to glycolysis as a set of potential therapeutic targets against malaria.

The lid domain is important, but not essential, for catalysis of Escherichia coli pyruvate kinase.

Pyruvate kinase catalyses the final step of the glycolytic pathway in central energy metabolism. The monomeric structure comprises three domains: a catalytic TIM-barrel, a regulatory domain involved in allosteric activation, and a lid domain that encloses the substrates. The lid domain is thought to close over the TIM-barrel domain forming contacts with the substrates to promote catalysis and may be involved in stabilising the activated state when the allosteric activator is bound. However, it remains unknown whether the lid domain is essential for pyruvate kinase catalytic or regulatory function. To address this, we removed the lid domain of Escherichia coli pyruvate kinase type 1 (PKTIM+Reg) using protein engineering. Biochemical analyses demonstrate that, despite the absence of key catalytic residues in the lid domain, PKTIM+Reg retains a low level of catalytic activity and has a reduced binding affinity for the substrate phosphoenolpyruvate. The enzyme retains allosteric activation, but the regulatory profile of the enzyme is changed relative to the wild-type enzyme. Analytical ultracentrifugation and small-angle X-ray scattering data show that, beyond the loss of the lid domain, the PKTIM+Reg structure is not significantly altered and is consistent with the wild-type tetramer that is assembled through interactions at the TIM and regulatory domains. Our results highlight the contribution of the lid domain for facilitating pyruvate kinase catalysis and regulation, which could aid in the development of small molecule inhibitors for pyruvate kinase and related lid-regulated enzymes.

Phosphoproteomic analysis of dengue virus infected U937 cells and identification of pyruvate kinase M2 as a differentially phosphorylated phosphoprotein.

Dengue virus (DENV) is an arthropod-borne Flavivirus that can cause a range of symptomatic disease in humans. There are four dengue viruses (DENV 1 to 4) and infection with one DENV only provides transient protection against a heterotypic virus. Second infections are often more severe as the disease is potentiated by antibodies from the first infection through a process known as antibody dependent enhancement (ADE) of infection. Phosphorylation is a major post-translational modification that can have marked effects on a number of processes. To date there has been little information on the phosphorylation changes induced by DENV infection. This study aimed to determine global phosphoproteome changes induced by DENV 2 in U937 cells infected under an ADE protocol. A 2-dimensional electrophoretic approach coupled with a phosphoprotein-specific dye and mass spectroscopic analysis identified 15 statistically significant differentially phosphorylated proteins upon DENV 2 infection. One protein identified as significantly differentially phosphorylated, pyruvate kinase M2 (PKM2) was validated. Treatment with a PKM2 inhibitor modestly reduced levels of infection and viral output, but no change was seen in cellular viral protein levels, suggesting that PKM2 acts on exocytic virus release. While the effect of inhibition of PKM2 was relatively modest, the results highlight the need for a greater understanding of the role of phosphoproteins in DENV infection.