Deciphering the ATP-binding mechanism(s) in NLRP-NACHT 3D models using structural bioinformatics approaches

Exploring the structural assembly of rice ADP-glucose pyrophosphorylase subunits using MD simulation

ADP-glucose pyrophosphorylase plays a pivotal role as an allosteric enzyme, essential for starch biosynthesis in plants. The higher plant AGPase comparises of a pair of large and a pair of small subunits to form a heterotetrameric complex. Growing evidence indicates that each subunit plays a distinct role in regulating the underlying mechanism of starch biosynthesis. In the rice genome, there are four large subunit genes (OsL1-L4) and three small subunit genes (OsS1, OsS2a, and OsS2b). While the structural assembly of cytosolic rice AGPase subunits (OsL2:OsS2b) has been elucidated, there is currently no such documented research available for plastidial rice AGPases (OsL1:OsS1). In this study, we employed protein modeling and MD simulation approaches to gain insights into the structural association of plastidial rice AGPase subunits. Our results demonstrate that the heterotetrameric association of OsL1:OsS1 is very similar to that of cytosolic OsL2:OsS2b and potato AGPase heterotetramer (StLS:StSS). Moreover, the yeast-two-hybrid results on OsL1:OsS1, which resemble StLS:StSS, suggest a differential protein assembly for OsL2:OsS2b. Thus, the regulatory and catalytic mechanisms for plastidial AGPases (OsL1:OsS1) could be different in rice culm and developing endosperm compared to those of OsL2:OsS2b, which are predominantly found in rice endosperm.

The balance between nuclear import and export of NLRC5 regulates MHC class I transactivation

Major histocompatibility complex (MHC) class I molecules play an essential role in regulating the adaptive immune system by presenting antigens to CD8 T cells. CITA (MHC class I transactivator), also known as NLRC5 (NLR family, CARD domain-containing 5), regulates the expression of MHC class I and essential components involved in the MHC class I antigen presentation pathway. While the critical role of the nuclear distribution of NLRC5 in its transactivation activity has been known, the regulatory mechanism to determine the nuclear localization of NLRC5 remains poorly understood. In this study, a comprehensive analysis of all domains in NLRC5 revealed that the regulatory mechanisms for nuclear import and export of NLRC5 coexist and counterbalance each other. Moreover, GCN5 (general control non-repressed 5 protein), a member of HATs (histone acetyltransferases), was found to be a key player to retain NLRC5 in the nucleus, thereby contributing to the expression of MHC class I. Therefore, the balance between import and export of NLRC5 has emerged as an additional regulatory mechanism for MHC class I transactivation, which would be a potential therapeutic target for the treatment of cancer and virus-infected diseases.

Brazilin is a natural product inhibitor of the NLRP3 inflammasome

Excessive or aberrant NLRP3 inflammasome activation has been implicated in the progression and initiation of many inflammatory conditions; however, currently no NLRP3 inflammasome inhibitors have been approved for therapeutic use in the clinic. Here we have identified that the natural product brazilin effectively inhibits both priming and activation of the NLRP3 inflammasome in cultured murine macrophages, a human iPSC microglial cell line and in a mouse model of acute peritoneal inflammation. Through computational modeling, we predict that brazilin can adopt a favorable binding pose within a site of the NLRP3 protein which is essential for its conformational activation. Our results not only encourage further evaluation of brazilin as a therapeutic agent for NLRP3-related inflammatory diseases, but also introduce this small-molecule as a promising scaffold structure for the development of derivative NLRP3 inhibitor compounds.

NLRP2 in health and disease

NLR family pyrin domain containing 2 (NLRP2) is a novel member of the Nod-like receptor (NLR) family. However, our understanding of NLRP2 has long been ambiguous. NLRP2 may have a role in the innate immune response, but its 'specific' functions remain controversial. Although NLRP2 can initiate inflammasome and promote inflammation, it can also downregulate inflammatory signals. Additionally, NLRP2 has been reported to function in the reproductive system and shows high expression in the placenta. However, the exact role of NLRP2 in the reproductive system is unclear. Here, we highlight the most current progress on NLRP2 in inflammasome activation, effector function and regulation of nuclear factor-κB. And we discuss functions of NLRP2 in inflammatory diseases, reproductive disorders and the potential implication of NLRP2 in human diseases.

Mechanism of NAIP-NLRC4 inflammasome activation revealed by cryo-EM structure of unliganded NAIP5

The nucleotide-binding domain (NBD), leucine rich repeat (LRR) domain containing protein family (NLR family) apoptosis inhibitory proteins (NAIPs) are cytosolic receptors that play critical roles in the host defense against bacterial infection. NAIPs interact with conserved bacterial ligands and activate the NLR family caspase recruitment domain containing protein 4 (NLRC4) to initiate the NAIP-NLRC4 inflammasome pathway. Here we found the process of NAIP activation is completely different from NLRC4. Our cryo-EM structure of unliganded mouse NAIP5 adopts an unprecedented wide-open conformation, with the nucleating surface fully exposed and accessible to recruit inactive NLRC4. Upon ligand binding, the winged helix domain (WHD) of NAIP5 undergoes roughly 20° rotation to form a steric clash with the inactive NLRC4, which triggers the conformational change of NLRC4 from inactive to active state. We also show the rotation of WHD places the 17-18 loop at a position that directly bind the active NLRC4 and stabilize the NAIP5-NLRC4 complex. Overall, these data provide structural mechanisms of inactive NAIP5, the process of NAIP5 activation and NAIP-dependent NLRC4 activation.

6-Shogaol Exhibits Anti-viral and Anti-inflammatory Activity in COVID-19-Associated Inflammation by Regulating NLRP3 Inflammasomes

Recent global health concern motivated the exploration of natural medicinal plant resources as an alternative target for treating COVID-19 infection and associated inflammation. In the current study, a phytochemical, 6-shogaol [1-(4-hydroxy-3-methoxyphenyl)dec-4-en-3-one; 6-SHO] was investigated as a potential anti-inflammatory and anti-COVID-19 agent. In virus release assay, 6-SHO efficiently (94.5%) inhibited SARS-CoV2 replication. When tested in the inflammasome activation model, 6-SHO displayed mechanistic action by regulating the expression of the inflammasome pathway molecules. In comparison to the existing drugs, remdesivir and hydroxy-chloroquine, 6-SHO was not only found to be as effective as the standard anti-viral drugs but also much superior and safe in terms of predicted physicochemical properties and clinical toxicity. Comparative molecular dynamics simulation demonstrated a stable interaction of 6-SHO with NLRP3 (the key inflammasome regulator) in the explicit water environment. Overall, this study provides important cues for further development of 6-SHO as potential anti-inflammatory and anti-viral therapeutic agents.

ATP-binding and hydrolysis of human NLRP3

The innate immune system uses inflammasomal proteins to recognize danger signals and fight invading pathogens. NLRP3, a multidomain protein belonging to the family of STAND ATPases, is characterized by its central nucleotide-binding NACHT domain. The incorporation of ATP is thought to correlate with large conformational changes in NLRP3, leading to an active state of the sensory protein. Here we analyze the intrinsic ATP hydrolysis activity of recombinant NLRP3 by reverse phase HPLC. Wild-type NLRP3 appears in two different conformational states that exhibit an approximately fourteen-fold different hydrolysis activity in accordance with an inactive, autoinhibited state and an open, active state. The impact of canonical residues in the nucleotide binding site as the Walker A and B motifs and sensor 1 and 2 is analyzed by site directed mutagenesis. Cellular experiments show that reduced NLRP3 hydrolysis activity correlates with higher ASC specking after inflammation stimulation. Addition of the kinase NEK7 does not change the hydrolysis activity of NLRP3. Our data provide a comprehensive view on the function of conserved residues in the nucleotide-binding site of NLRP3 and the correlation of ATP hydrolysis with inflammasome activity.

Analysis of the inflammasome-forming protein NLRP3 provides insights into the function of conserved residues in the ATP-binding site of NLRP3 and the correlation of ATP hydrolysis with inflammasome activation.

Probing the effect of NEK7 and cofactor interactions on dynamics of NLRP3 monomer using molecular simulation

The NLRP3 inflammasome is a cytoplasmic complex that regulates the activation of inflammatory cytokines and, given its implication in a range of diseases, is an important therapeutic target. The cofactor ATP and the centrosomal kinase NEK7 are important for NLRP3 activation. Here we have constructed and simulated computational models of full‐length monomeric NLRP3 to shed light on the importance of NEK7 and cofactor interactions for its conformation and dynamics in aqueous solution. We find that molecular dynamics simulation reproduces well the features of the recently published cryo‐EM structure of the ADP‐bound NLRP3–NEK7 complex; on the removal of NEK7, the NLRP3 molecule adopts a more compact closed form during simulations. Replacement of ADP by ATP promotes a rearrangement of hydrogen‐bonding interactions, domain interfaces, and a degree of opening of the NLRP3 conformation. We also examine the dynamics of an acidic loop of the LRR domain of NLRP3, which samples in a region observed in the NEK7‐bound cryo‐EM structure but not in an oligomeric form of inactive NLRP3. During the molecular dynamics simulations of NLRP3, we find some plasticity in its topology that suggests access routes for ATP to the cofactor pocket not immediately evident from the existing NEK7‐bound cryo‐EM structure. These computed dynamical trajectories of NLRP3 provide insight into coordinates of deformation that may be key for cofactor binding and inflammasome activation.

Activation and Pharmacological Regulation of Inflammasomes

Inflammasomes are intracellular signaling complexes of the innate immune system, which is part of the response to exogenous pathogens or physiological aberration. The multiprotein complexes mainly consist of sensor proteins, adaptors, and pro-caspase-1. The assembly of the inflammasome upon extracellular and intracellular cues drives the activation of caspase-1, which processes pro-inflammatory cytokines IL-1β and IL-18 to maturation and gasdermin-D for pore formation, leading to pyroptosis and cytokine release. Inflammasome signaling functions in numerous infectious or sterile inflammatory diseases, including inherited autoinflammatory diseases, metabolic disorders, cardiovascular diseases, cancers, neurodegenerative disorders, and COVID-19. In this review, we summarized current ideas on the organization and activation of inflammasomes, with details on the molecular mechanisms, regulations, and interventions. The recent developments of pharmacological strategies targeting inflammasomes as disease therapeutics were also covered.

The immune function of a NLR like gene, LvNLRPL1, in the Pacific whiteleg shrimp Litopenaeus vannamei

NOD-like receptors (NLRs) are a kind of pattern recognition receptors, which are vital for detection of pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs) and then trigger downstream immune responses in vertebrates. Although many NLR like genes have been identified in invertebrates in recent years, knowledge about their immune functions is still very limited. In the present study, a NLR like gene, designated as LvNLRPL1, was identified in Litopenaeus vannamei. It was widely expressed in multiple tissues and responsive to the infection of Vibrio parahaemolyticus. Knockdown of LvNLRPL1 could accelerate the proliferation of Vibrio in hepatopancreas and increase the mortality rate of shrimp after Vibrio infection. Meanwhile, knockdown of LvNLRPL1 also up-regulated the expression of Caspase 2, 3 and 5 in hemocytes, which caused apoptosis of more hemocytes. These results indicated that LvNLRPL1 played important immune functions in shrimp during Vibrio infection through regulating the apoptosis of hemocytes in shrimp. To our knowledge, this is the first time to reveal the immune function of a NLR like gene in crustaceans.

Structural Elucidation of Inter-CARD Interfaces involved in NOD2 Tandem CARD Association and RIP2 Recognition

Nucleotide-binding and oligomerization domain-containing protein 2 (NOD2) recognizes the muramyl dipeptide and activates the NF-κB signaling cascade following its interaction with receptor-interacting protein 2 (RIP2) via caspase recruitment domains (CARDs). The NOD2-RIP2 interaction is not understood well due to inadequate structural information. Using comparative modeling and multimicrosecond timescale molecular dynamics simulations, we have demonstrated the association of NOD2-CARDs (CARDa-CARDb) and their interaction with RIP2^CARD. Our results suggest that a negatively charged interface of NOD2^CARDa and positively charged type-Ia interface of NOD2^CARDb are crucial for CARDa-CARDb association and the type-Ia interface of NOD2^CARDa and type-Ib interface of RIP2^CARD predicted to be involved in 1:1 CARD-CARD interaction. Moreover, the direct interaction of NOD2^CARDb with RIP2^CARD signifies the importance of both CARDs of NOD2 in RIP2-mediated CARD-CARD interaction. Altogether, the structural results could help in understanding the underlying molecular details of the NOD2-RIP2 association in higher and lower eukaryotes.

Cellular origins of dsRNA, their recognition and consequences

Double-stranded RNA (dsRNA) is associated with most viral infections - it either constitutes the viral genome (in the case of dsRNA viruses) or is generated in host cells during viral replication. Hence, nearly all organisms have the capability of recognizing dsRNA and mounting a response, the primary aim of which is to mitigate the potential infection. In vertebrates, a set of innate immune receptors for dsRNA induce a multitude of cell-intrinsic and cell-extrinsic immune responses upon dsRNA recognition. Notably, recent studies showed that vertebrate cells can accumulate self-derived dsRNAs or dsRNA-like species upon dysregulation of several cellular processes, activating the very same immune pathways as in infected cells. On the one hand, such aberrant immune activation in the absence of infection can lead to pathogenesis of immune disorders, such as Aicardi-Goutières syndrome. On the other hand, the same innate immune reaction can be induced in a controlled setting for a therapeutic benefit, as occurs in immunotherapies. In this Review, we describe mechanisms by which immunostimulatory dsRNAs are generated in mammalian cells, either by viruses or by the host cells, and how cells respond to them, with the focus on recent developments regarding the role of cellular dsRNAs in immune modulation.

Apurinic/apyrimidinic endonuclease 1/reduction-oxidation effector factor-1 (APE1) regulates the expression of NLR family pyrin domain containing 3 (NLRP3) inflammasome through modulating transcription factor NF-κB and promoting the secretion of inflammatory mediators in macrophages

Background

Inflammatory mediators play an important role in the occurrence, development, and metastasis of tumors. The aim of the present study was to elucidate the effect of apurinic/apyrimidinic endonuclease 1/reduction-oxidation effector factor-1 (APE1) on inflammatory mediator secretion, which is dependent on the APE1-mediated NLR family pyrin domain containing 3 (NLRP3) regulatory mechanism.

Methods

The human myeloid leukemia mononuclear cell line (THP-1) cells were cultured and polarized to M2 subset macrophages. Enzyme-linked immunosorbent assay was used for determining tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-18, IL-10, and IL-33 levels. Reverse transcription–polymerase chain reaction and western blot were used for evaluating TNF-α, NLR family pyrin domain containing 1 (NLRP1), NLRP3, caspase-1, and apoptosis-associated speck-like protein containing a card expression. Plasmid silencing APE1 gene (APE1^shRNA) was synthesized and packaged into lentiviral. For activating inflammasomes, M2-type THP-1 cells were transfected with lentiviral vector APE1^shRNA incubated with lipopolysaccharide (LPS) (100 ng/mL)/APE1 inhibitor (E3330, 20 µM) and ATP. Electrophoretic mobility shift assay and dual-luciferase reporter assay were used for determining the interaction between NLRP3 and nuclear factor-κB (NF-κB) molecule.

Results

APE1 significantly induced LPS-induced pro-inflammatory cytokine production, including TNF-α, IL-1β, and IL18, compared with THP-1 cells without APE1 treatment (P<0.05). APE1 promoted LPS-induced NLRP3 inflammasome activation by modulating the gene transcription of NLRP3-associated molecules. APE1 enhanced LPS-induced NLRP3 inflammasome activation by regulating NLRP3 and caspase-1 protein expression. APE1 improved NLRP3 activity by modulating the interaction between NLRP3 and NF-κB, and the modulation of NF-κB. APE1 promoted LPS-induced NLRP3 inflammasome activation through an NF-κB-dependent pathway.

Conclusions

APE1 regulates the expression of NLRP3 by modulating transcription factor NF-κB and further promoting the secretion of inflammatory mediators IL-1β and IL-18 in macrophages. The findings of the present study provide theoretical and experimental bases for the design of tumor-associated macrophage (TAM)-targeted therapy, with APE1 as the target molecule.

APE1/Ref-1 - One Target with Multiple Indications: Emerging Aspects and New Directions

In the realm of DNA repair, base excision repair (BER) protein, APE1/Ref-1 (Apurinic/Apyrimidinic Endonuclease 1/Redox Effector - 1, also called APE1) has been studied for decades. However, over the past decade, APE1 has been established as a key player in reduction-oxidation (redox) signaling. In the review by Caston et al. (The multifunctional APE1 DNA repair-redox signaling protein as a drug target in human disease), multiple roles of APE1 in cancer and other diseases are summarized. In this Review, we aim to expand on the contributions of APE1 to various diseases and its effect on disease progression. In the scope of cancer, more recent roles for APE1 have been identified in cancer cell metabolism, as well as chemotherapy-induced peripheral neuropathy (CIPN) and inflammation. Outside of cancer, APE1 signaling may be a critical factor in inflammatory bowel disease (IBD) and is also an emergent area of investigation in retinal ocular diseases. The ability of APE1 to regulate multiple transcription factors (TFs) and therefore multiple pathways that have implications outside of cancer, makes it a particularly unique and enticing target. We discuss APE1 redox inhibitors as a means of studying and potentially combating these diseases. Lastly, we examine the role of APE1 in RNA metabolism. Overall, this article builds on our previous review to elaborate on the roles and conceivable regulation of important pathways by APE1 in multiple diseases.

Inhibiting the NLRP3 Inflammasome

Inflammasomes are protein complexes which are important in several inflammatory diseases. Inflammasomes form part of the innate immune system that triggers the activation of inflammatory cytokines interleukin (IL)-1β and IL-18. The inflammasome most studied in sterile inflammation and non-communicable disease is the NLRP3 inflammasome. Upon activation by diverse pathogen or disease associated signals, NLRP3 nucleates the oligomerization of an adaptor protein ASC forming a platform (the inflammasome) for the recruitment and activation of the protease caspase-1. Active caspase-1 catalyzes the processing and release of IL-1β and IL-18, and via cleavage of the pore forming protein gasdermin D can drive pyroptotic cell death. This review focuses on the structural basis and mechanism for NLRP3 inflammasome signaling in the context of drug design, providing chemical structures, activities, and clinical potential of direct inflammasome inhibitors. A cryo-EM structure of NLRP3 bound to NEK7 protein provides structural insight and aids in the discovery of novel NLRP3 inhibitors utilizing ligand-based or structure-based approaches.

Computational Modeling of NLRP3 Identifies Enhanced ATP Binding and Multimerization in Cryopyrin-Associated Periodic Syndromes

Cyropyrin-associated periodic syndromes (CAPS) are clinically distinct syndromes that encompass a phenotypic spectrum yet are caused by alterations in the same gene, NLRP3. Many CAPS cases and other NLRP3-autoinflammatory diseases (NLRP3-AIDs) are directly attributed to protein-coding alterations in NLRP3 and the subsequent dysregulation of the NLRP3 inflammasome leading to IL-1β-mediated inflammatory states. Here, we used bioinformatics tools, computational modeling, and computational assessments to explore the proteomic consequences of NLRP3 mutations, which potentially drive NLRP3 inflammasome dysregulation. We analyzed 177 mutations derived from familial cold autoinflammatory syndrome (FCAS), Muckle-Wells Syndrome (MWS), and the non-hereditary chronic infantile neurologic cutaneous and articular syndrome, also known as neonatal-onset multisystem inflammatory disease (CINCA/NOMID), as well as other NLRP3-AIDs. We found an inverse relationship between clinical severity and the severity of predicted structure changes resulting from mutations in NLRP3. Bioinformatics tools and computational modeling revealed that NLRP3 mutations that are predicted to be structurally severely-disruptive localize around the ATP binding pocket and that specific proteo-structural changes to the ATP binding pocket lead to enhanced ATP binding affinity by altering hydrogen-bond and charge interactions. Furthermore, we demonstrated that NLRP3 mutations that are predicted to be structurally mildly- or moderately-disruptive affect protein-protein interactions, such as NLRP3-ASC binding and NLRP3-NLRP3 multimerization, enhancing inflammasome formation and complex stability. Taken together, we provide evidence that proteo-structural mechanisms can explain multiple mechanisms of inflammasome activation in NLRP3-AID.

ATP-Binding and Hydrolysis in Inflammasome Activation

The prototypical model for NOD-like receptor (NLR) inflammasome assembly includes nucleotide-dependent activation of the NLR downstream of pathogen- or danger-associated molecular pattern (PAMP or DAMP) recognition, followed by nucleation of hetero-oligomeric platforms that lie upstream of inflammatory responses associated with innate immunity. As members of the STAND ATPases, the NLRs are generally thought to share a similar model of ATP-dependent activation and effect. However, recent observations have challenged this paradigm to reveal novel and complex biochemical processes to discern NLRs from other STAND proteins. In this review, we highlight past findings that identify the regulatory importance of conserved ATP-binding and hydrolysis motifs within the nucleotide-binding NACHT domain of NLRs and explore recent breakthroughs that generate connections between NLR protein structure and function. Indeed, newly deposited NLR structures for NLRC4 and NLRP3 have provided unique perspectives on the ATP-dependency of inflammasome activation. Novel molecular dynamic simulations of NLRP3 examined the active site of ADP- and ATP-bound models. The findings support distinctions in nucleotide-binding domain topology with occupancy of ATP or ADP that are in turn disseminated on to the global protein structure. Ultimately, studies continue to reveal how the ATP-binding and hydrolysis properties of NACHT domains in different NLRs integrate with signaling modules and binding partners to control innate immune responses at the molecular level.

Understanding the thermal response of rice eukaryotic transcription factor eIF4A1 towards dynamic temperature stress: insights from expression profiling and molecular dynamics simulation

Eukaryotic translation initiation factors (eIFs) are the group of regulatory proteins that are involved in the initiation of translation events. Among them, eIF4A1, a member of the DEAD-box RNA helicase family, participates in a wide spectrum of activities which include, RNA splicing, ribosome biogenesis, and RNA degradation. It is well known that ATP-binding and subsequent hydrolysis activities are crucial for the functionality of such helicases. Although the stress-responsive upregulation of eIF4A1 has been reported in plants during stress, it is difficult to anticipate the functionality of the corresponding protein product. Therefore, to understand the activity of eIF4A1 in rice in response to temperature stress, we first conducted an expression analysis of the gene and further investigated the structural stability of the eIF4A1-ATP/Mg²⁺ complex through molecular dynamics (MD) simulations at different temperature conditions (277 K, 300 K, and 315 K). Our results demonstrated a three to fourfold increased expression of rice eIF4A1 both in root and shoot at 42 °C compared to control. Furthermore, the MD simulation portrayed strong ATP/Mg²⁺ binding at a higher temperature in comparison to control and cold temperature. Overall, the increased expression pattern of eIF4A1 and strong ATP/Mg²⁺ binding at higher temperature indicated the heat stress-tolerant capacity of the gene in rice. The results from our study will help in understanding the activity of gene and guide the researchers for screening of novel stress inducible candidate genes for the engineering of temperature stress tolerant plants.Communicated by Ramaswamy H. Sarma.

Molecular characterization, constitutive expression and GTP binding mechanism of Cirrhinus mrigala (Hamilton, 1822) Myxovirus resistance (Mx) protein

Myxovirus resistance (Mx) proteins represents the subclass of the dynamin superfamily of large Guanosine triphosphates (GTPases), play esential role in intracellular vesicle trafficking, endocytosis, organelle homeostasis and mitochondria distribution. These proteins are key players of the vertebrate immune system, induced by type-I and type-III interferons (IFN) of infected host and inhibit viral replication by sequestering its nucleoprotein. In the present study, we report the sequencing and characterization of Cirrhinus mrigala Mx protein (CmMx) for the first time and observed its constitutive expression in different tissues for a period of fourteen days. The synthetic peptide, LSGVALPRGTGI, was dissolved in PBS and injected into a rabbit and the antibody raised against CmMx was used to study the level of its expression. The full length of the CmMx cDNA is 2244 bp with a molecular mass of 70.9 kDa and a predicted isoelectric point of 8.25. The 627 amino acids polypeptide formed of three main functional domains: N-terminal GTPase domain (GD), a middle domain (MD) and GTPase effector domain (GED) with carboxy terminal leucine zipper motif. The 3D models of CmMx protein was modeled based on available close structural homologs and further validated through molecular dynamics (MD) simulations. MD study revealed the importance of G-domain responsible for recognition of GTP, which perfectly corroborate with earlier studies. MM/PBSA binding free energy analysis displayed that van der Waals and electrostatic energy were the key driving force behind molecular recognition of GTP by CmMx protein. The results from this study will illuminate more lights into the ongoing research on myxovirus resistance protein and its role in inhibition of viral replication in other eukaryotic system as well.

Effects of phosphorylation on the NLRP3 inflammasome

The pyrin domain containing Nod-like receptors (NLRPs) are a family of pattern recognition receptors known to regulate an array of immune signaling pathways. Emergent studies demonstrate the potential for regulatory control of inflammasome assembly by phosphorylation, notably NLRP3. Over a dozen phosphorylation sites have been identified for NLRP3 with many more suggested by phosphoproteomic studies of the NLRP family. Well characterized NLRP3 phosphorylation events include Ser198 by c-Jun terminal kinase (JNK), Ser295 by protein kinase D (PKD) and/or protein kinase A (PKA), and Tyr861 by an unknown kinase but is dephosphorylated by protein tyrosine phosphatase non-receptor 22 (PTPN22). Since the PKA- and PKD-dependent phosphorylation of NLRP3 at Ser295 is best characterized, we provide detailed review of this aspect of NLRP3 regulation. Phosphorylation of Ser295 can attenuate ATPase activity as compared to its dephosphorylated counterpart, and this event is likely unique to NLRP3. In silico modeling of NLRP3 is useful in predicting how Ser295 phosphorylation might impact upon the structural topology of the ATP-binding domain to influence catalytic activity. It is important to gain as complete understanding as possible of the complex phosphorylation-mediated mechanisms of regulation for NLRP3 in part because of its involvement in many pathological processes.