key: cord-0984977-4vcn8c3n
authors: Teixeira, S.C.; Borges, B.C.; Oliveira, V.Q.; Carregosa, L.S.; Bastos, L.A.; Santos, I.A.; Jardim, A.C.G.; Freire, F.M.; Martins, L.; Rodrigues, V.M.; Lopes, D.S.
title: Insights into the antiviral activity of phospholipases A(2) (PLA(2)s) from snake venoms
date: 2020-07-19
journal: Int J Biol Macromol
DOI: 10.1016/j.ijbiomac.2020.07.178
sha: dd35b22492fdf8187990b29116dda9dce53018f3
doc_id: 984977
cord_uid: 4vcn8c3n

Viruses are associated with several human diseases that infect a large number of individuals, hence directly affecting global health and economy. Owing to the lack of efficient vaccines, antiviral therapy and emerging resistance strains, many viruses are considered as a potential threat to public health. Therefore, researches have been developed to identify new drug candidates for future treatments. Among them, antiviral research based on natural molecules is a promising approach. Phospholipases A(2) (PLA(2)s) isolated from snake venom have shown significant antiviral activity against some viruses such as Dengue virus, Human Immunodeficiency virus, Hepatitis C virus and Yellow fever virus, and have emerged as an attractive alternative strategy for the development of novel antiviral therapy. Thus, this review provides an overview of remarkable findings involving PLA(2)s from snake venom that possess antiviral activity, and discusses the mechanisms of action mediated by PLA(2)s against different stages of virus replication cycle. Additionally, molecular docking simulations were performed by interacting between phospholipids from Dengue virus envelope and PLA(2)s from Bothrops asper snake venom. Studies on snake venom PLA(2)s highlight the potential use of these proteins for the development of broad-spectrum antiviral drugs.

J o u r n a l P r e -p r o o f addition, the lysophospholipids are also related to a variety of physiological roles in cell signaling [53, 58] . PLA 2 s are classified into six groups: cytosolic (cPLA 2 ), Ca( 2+ )-independent (iPLA 2 ), platelet-activating factor acetylhydrolase (PAF-AH), lysosomal PLA 2 (LyPLA 2 ), adipose specific PLA 2 (AdPLA 2 ) and secretory PLA2 (sPLA 2 ) [53] . In addition, the sPLA 2 s are divided into the following groups: IA, IB, IIA, IIB, IIC, IID, IIE, IIF, III, V, IX, X, XIA, XIB, XII, XIII and XIV [53, 54] . PLA 2 s from snake venom belong to the group of secreted type of enzymes (sPLA 2 s) and can be classified into the structural group IB (in Elapidae snake venoms), which exhibits homology to the mammalian pancreatic juice PLA 2 , and also into the group IIA (in Viperidae snake venoms), that is homologous to the mammalian ‗inflammatory' PLA 2 [59] . Although the PLA 2 s family is more frequent in snake venom, recent proteome studies have demonstrated that Phospholipases B (PLB) can also be found in snake venom [60] [61] [62] . sPLA 2 s are proteins with molecular mass of about 14 kDa, pH optimum at 7 and share a conserved catalytic mechanism based on a His/Asp dyad using Ca 2+ as an essential cofactor for the catalytic activity. Group II of sPLA 2 s presents an extended Cterminal segment (5-7 amino acids) [63, 64] and is subdivided into two main subgroups, depending on the amino acid residue at position 49 in the protein primary structure. Aspartate (Asp49 or D49) sPLA 2 s are enzymatically active, while lysine (Lys49 or K49) sPLA 2 s present no enzymatic activity [65] [66] [67] . However, there are further variants, as the serine (Ser49), asparagine (Asn49) or arginine (Arg49) [68] [69] [70] .

Lys49 PLA 2 s are devoid of catalytic activity due to their inability to bind Ca 2+ , a key cofactor for PLA 2 activity. Although the lack of enzymatic activity, the Lys49 PLA 2 homologues have shown to display toxicity, especially myotoxicity [67] . The toxicity of Lys49 proteins can be related to a cluster of cationic and hydrophobic/aromatic amino acid residues located at the C-terminal region of these toxins [71, 72] .

Therefore, the cytotoxicity of sPLA 2 is probably mediated by the interaction between the C-terminal region and the plasma membrane [73, 74] . Moreover, the PLA 2 effects can be mediated through the integrins and other receptors, such as vascular endothelial growth factor receptor-2 (VEGFR-2), and M-Type receptors [75] [76] [77] .

J o u r n a l P r e -p r o o f sPLA 2 s from snake venom can act on cell membranes of specific tissues inducing several pharmacological actions such as myotoxicity, neurotoxicity, cardiotoxicity, platelet aggregation activation or inhibition, hypotension, edema among others [57, 79] . In this scenario, these proteins have emerged as a potential therapeutic model, since numerous studies have focused on their microbicidal [80] , antitumor [81] [82] [83] , antiangiogenesis [84] , antiparasitic [85] [86] [87] and antiviral activities [51] .

The development of efficient antiviral therapies has become a global health emergency. In this sense, several researches have demonstrated the antiviral activity of sPLA 2 s from snake venom against human viruses, including DENV, YFV, HCV and others [88] [89] [90] [91] [92] . Hence, the present review aimed to summarize the sPLA 2 s from snake venom that were previously described to possess antiviral activity, highlighting the mechanisms of action of sPLA 2 s against different stages of virus replication cycle ( Table 1) .

The venom of Crotalus durissus terrificus (C. d. terrificus), a South American rattlesnake, is composed by a large number of molecules with biological activities, such as crotoxin, crotamin, PLA 2 -inter-cro‖ (PLA 2 -IC), convulxin and gyroxin [93, 94] .

Crotoxin, which comprehends more than a half of the dry weight of C. d. terrificus venom, is a heterodimeric compound composed by the PLA 2 -CB (a basic phospholipase component) and crotapotin (an acidic nontoxic catalytically inactive protein) [95, 96] .

Villarrubia and coworkers [97] reported that crotoxin has anti-HIV (HIV-1, 2) effect by a direct interaction with Gag p24 glycoprotein on the viral surface, which appears to abrogate the HIV anchoring to host cell.

Furthermore, Muller and colleagues [88] working with diverse sPLA 2 s isolated from C. d. terrificus venom explored different approaches to unveil the potent antiviral activity mediated by crotoxin, PLA 2 -CB and PLA 2 -IC against DENV-2 and YFV (enveloped virus). The authors demonstrated that all investigated sPLA 2 s promoted a significant inhibition of DENV-2 and YFV entry into VERO E6 cells by a direct action on the viral particles (virucidal activity), and by interfering in the adsorption and internalization steps (early stages of the viral replication cycle) [88] . Besides that, cell J o u r n a l P r e -p r o o f pretreatment with three sPLA 2 s was able to protect host cell against flaviviruses infection after 7 days by the reduction in the number of plaque formation. Interestingly, sPLA 2 s treatment after viral infection promoted an enhancement of load viral, indicating that antiviral effect occurs in the early stages of viral infection [88] . In addition, the researchers gained insights into the role of catalytic sites of the tested sPLA 2 s, proposing the use of a sPLA 2 without catalytic activity (BthTX-I) isolated from Bothrops jararacussu [98] .

BthTX-I revealed antiviral activity against YFV and DENV-2 in the virucidal, adsorption and internalization assays. Interestingly, as shown to other catalyticallyactive sPLA 2 s at 100 ng/L, BthTX-I at the same concentration was also able to inhibit YFV entry by virucidal activity (100%), interfering in adsorption (77%) and internalization (78%) [88] . Although BthTX-I showed antiviral activity, the effective concentration 50% (EC50) values obtained for this toxin were extremely higher when Togaviridae family). However, these compounds did not show virucidal effect against Coxsackie B5 virus (CV-B5; Picornaviridae family; non-enveloped virus), hence suggesting that the possible antiviral action occurs upon the lipid bilayer viral envelope [89] . To corroborate these findings, it was demonstrated that preincubating DENV-2 with PLA 2 -CB or crotoxin resulted in an increase of exposure and degradation of viral RNA [89] . Also, Russo and collaborators [99] expressed two recombinant PLA 2 -CB isoforms through a prokaryotic system and noted that both rPLA 2 -CB1 and rPLA 2 -CB2 maintained the viral inhibitory activity against CHIKV, DENV-2, YFV and ZIKV when compared to the native sPLA 2 -CB. Additionally, Muller and colleagues [88, 89] J o u r n a l P r e -p r o o f suggested that the mechanism of action of PLA 2 -CB isolated from C. t. terrificus against DENV can occur through an interaction with components on the host cell surface or mainly due to the glycerophospholipid cleavage on the virus envelope, destabilizing viral E proteins and resulting in the viral envelope disruption and RNA viral exposure before the infection of host cells.

In order to gain insights into the antiviral mechanism of sPLA 2 s obtained from C. t. terrificus, Shimizu and colleagues [90] showed that PLA 2 -CB inhibited HCVcc JFH-1 virus strain entry and replication in Huh 7.5 cells, and crotoxin blocked virus entry and release, suggesting that these proteins possess multiple antiviral effects against HCV. Moreover, the authors also reported that PLA 2 -CB significantly decrease the levels of lipid droplets, which are essential for the HCV replication complex, and reduced the levels of HCV NS5A protein due to the replication inhibition, evidencing that besides the action on virus entry, PLA 2 -CB is able to disrupt HCV replication probably by an interference in lipid metabolism of host cell [90, 100, 101] .

Both BlK-PLA 2 (Lys49 sPLA 2 s) and BlD-PLA 2 (Asp49 sPLA 2 s) are two basic sPLA 2 s isolated from Bothrops leucurus venom, a pit viper (white-tailed-jararaca) commonly found in the northeast of Brazil [102] . Cecilio and coworkers [91] showed that the pretreatment of LLC-MK2 cells (Rhesus Monkey Kidney Epithelial cells) with each isoform of Bl-PLA 2 followed by viral infection was able to inhibit DENV infectivity (serotypes 1, 2 and 3), measured by qRT-PCR quantification of the DENV viral load in the cell supernatants after virus infection. On the other hand, Bl-PLA 2 s treatment after viral entry was not capable of inhibiting viral replication, then suggesting that the antiviral effect occurs upon components on the surface of the host cell membrane. The authors did not assess the potential virucidal mechanism of Bl-PLA 2 s against DENV. However, they suggested that the possible mechanism of action of Bl-PLA 2 s does not depend exclusively on their catalytic site. The Lys49-BlK-PLA 2 treatment was able to interfere in the viral load, indicating that the functional effect mediated by Bl-PLA 2 s also may occur due to the presence of pharmacological domains on the enzyme surface that would allow the interaction with host cell proteins, as well as the enzymatic activity [91] . The authors hypothesized that the DENV RNA level reduction is mediated by the intracellular action of Bl-PLA 2 s due to the higher J o u r n a l P r e -p r o o f penetrability capacity of basic sPLA 2 s, in comparison to neutral and acidic enzymes [91, 103] .

Bothrops asper is a viperid specie found in Central America and its venom contains significant concentrations of acid and basic sPLA 2 enzymes [104] . The B.

asper venom has both the basic enzymatically-active sPLA 2 (Mt-I) and the catalyticallyinactive sPLA 2 -like protein (Mt-II) [74] .

Brenes and collaborators [92] investigated the antiviral potential triggered by both Mt-I and Mt-II isoforms isolated from B. asper venom. The authors showed that these sPLA 2 s at concentration of 50 g/mL completely blocked virus entry by a virucidal action against members of Flaviviridae family, such as DENV and YFV, while exhibited moderate to negligible effects against other enveloped viruses (HSV-1, HSV-2, Influenza A H3N2 and Vesicular stomatitis VSV) or non-enveloped viruses (Sabin Poliovirus 1, 2 and 3). Interestingly, for the half-maximum virucidal activity against DENV-2, Mt-I required 1.5 ng/mL, while Mt-II acted at 2768 ng/mL, revealing that Mt-I is extremely more potent than Mt-II [92] . Investigating the role of the enzymatic activity in the inhibitory effect upon DENV-2, it was promoted the inactivation of the catalytic activity of Mt-I with p-bromophenacyl bromide (pBPB). The data showed that the chemical inactivation of Mt-I resulted in a reduction of the virucidal potency, indicating the relevant role of the enzymatic action against viral infection [92] . Even without enzymatic activity, the C-terminal region of Mt-II, which encompasses the amino acid residues 115-129, is responsible for the membrane-permeabilizing effect caused in many cellular types [67] , as well as its bactericidal activity [105] .

Notwithstanding that, the authors demonstrated that, even at high concentrations, the synthetic peptide -p115‖ corresponding to the Cterminal region of Mt-II (amino acid residues 115-129) did not inhibit DENV-2 [92] . Thus, the authors speculate that the weak virucidal effect of Mt-II may be intrinsic or more possible related to a trace contamination with Mt-I, where the total chromatographic separation for these toxins is hardly achieved [92] .

In addition, it was suggested that Mt-I acts by a direct virucidal mechanism that depends on its enzymatic activity, which may hydrolyze viral envelope phospholipids and disrupt the viral envelope of flaviviruses leading to the impairment of the infection.

Also, the mode of action of Mt-I and Mt-II is not related to an effect on host cell, since J o u r n a l P r e -p r o o f cell treatment after infection did not interfere in viral replication [92] . Furthermore, in a pretreatment assay, it was demonstrated a partial reduction of viral plaques, that may be explained by a slight cytotoxic action of Mt-I on cells [92] . Finally, the higher antiviral activity of Mt-I against Flaviviridae viruses in comparison to other enveloped virus families may be related to the specific structural organization, physicochemical composition, curvature and fluidity of viral envelope from flaviviruses, which may positively affect the catalytic activity of Mt-I against this family [106] .

In a previous study, Fenard and colleagues [107] demonstrated anti-HIV-1 effects of different sPLA 2 s from snake venom, such as taipoxin (Oxyuranus scutellatus venom), Nmm CMIII (Naja mossambica mossambica venom) [108, 109] and nigexine (Naja nigricollis venom) [110] . Investigating the possible mode of action of some of these sPLA 2 s, it was observed that despite their enzymatic activity, Nmm CMIII and taipoxin did not show virucidal effects against HIV-1, but promoted an efficient inhibition of HIV-1 entry by preventing the intracellular release of HIV-1 Gap p24 proteins from the viral capsid [107] .

The blockage of HIV entry appears to not depend exclusively on sPLA 2 s catalytically active, which was confirmed through two manners: i) the use of inhibitors of sPLA 2 s activity, such as phenacylbromide, aristolochic acid or oleoyloxyethylphosphocholine, that were not able to interfere in the blockage of virus entry mediated by sPLA 2 s; ii) the use of cleavage products of sPLA 2 s, such as arachidonic acid, lysophosphatidylethanolamine, lysophosphatidic acid, oleoyllysophosphatidylcholine and palmitoyl-lysophosphatidylcholine, which were also not able to inhibit virus entry [107] . In addition, competition binding assays between sPLA 2 s and host cells showed extremely low dissociation constant (K) values for Nmm CMIII , taipoxin and nigexine, suggesting that the inhibition of HIV-1 entry triggered by sPLA 2 s is more probably linked to sPLA 2 s binding membrane receptors of host cells than their enzymatic activity [107, 111] .

CM-II-sPLA 2 is a secreted PLA 2 isoform isolated from Naja mossambica mossambica venom [112, 113] . Recently, Chen and coworkers [114] reported that this and CV-B3 (Coxsackievirus B3; Picornaviridae) [114] .

The disruption of viral envelope by CM-II-sPLA 2 appears to be directly related to its enzymatic activity, which was confirmed by the use of manoalide (a specific sPLA 2 inhibitor) that inhibited the virucidal activity of CM-II-sPLA 2 against HCV and DENV [114] . Moreover, the selectivity of CM-II-sPLA 2 for virus buds through endoplasmic reticulum may be related to the differences in the phospholipid contents and physicochemical characteristics (thickness and sturdiness) that can differ among the different routes of viral budding, which would enhance the sensitivity to CM-II-sPLA 2 mediated by hydrolysis against HCV, DENV and JEV [114] [115] [116] [117] .

Findings from the current literature about the antiviral activity of toxins (Table   1) It is proposed that the potent virucidal activity of sPLA 2 s against enveloped viruses is likely associated with the ability that catalytically-active sPLA 2 s have to cleave glycerophospholipids in the virus lipid envelope, and it is reasonable to propose that sPLA 2 s also present domains that are capable to interact with viral envelope components, which could lead to viral envelope disruption, hence resulting in exposure of the viral content (viral inactivation) and compromising the early stages of viral replication. Additionally, Muller and colleagues [88, 89] , through a steric and electrostatic analysis of the interaction of PLA 2 -CB with the DENV envelope lipid bilayer, showed that PLA 2 -CB probably accesses the DENV lipid bilayer through the pores found on each of the twenty 3-fold vertices in the E protein shell on the DENV surface, which would allow the glycerophospholipid cleavage on the virus envelope and destabilization of the E proteins. Interestingly, it has been demonstrated that the structural organization and lipid composition of viral envelope may influence the antiviral efficiency of some sPLA 2 s, suggesting that the virucidal mechanism mediated by sPLA 2 s is specific [92] .

Independent studies have revealed that sPLA 2 s such as crotoxin, PLA 2 -IC, PLA 2 -CB, Bl-PLA 2 and BthTX-I are also able to dramatically impact the entry, replication and release of viruses by targeting host cell components [88] [89] [90] [91] . To gain insights into these viral cycle stages, it was demonstrated that Nmm CMIII , taipoxin and nigexine prevented the intracellular release of HIV-1 Gap p24 proteins from the viral capsid (inhibition virus entry) by a direct binding to membrane receptors of host cells [107] . In addition, PLA 2 -CB was able to disrupt HCV replication probably by an interference in lipid metabolism of host cell [90] .

It was demonstrated through the use of both specific sPLA 2 inhibitors and the catalytically-inactive sPLA 2 s that the antiviral effect of the major tested catalyticallyactive sPLA 2 s, such as crotoxin, PLA 2 -IC, PLA 2 -CB, BlD-PLA 2 , Mt-I and CM-II-sPLA 2 is significantly higher when presented their functional catalytic site to sPLA 2 s with no enzymatic activity (BthTX-I, BlK-PLA 2 and Mt-II) [88, 91, 92, 114] .

In order to corroborate with the data from the current literature, we performed docking simulations between the sPLA 2 s from Bothrops asper venom and three phospholipids found in the DENV envelope, which are 1-Palmitoyl-2oleoylphosphatidylcholine (POPC), 1-palmitoyl-2-oleoylphosphatidylethanolamine (POPE) and 1-Palmitoyl-2-oleoylphosphatidylserine (POPS) [118] . The molecular docking simulations were done by using the 3D crystal structure of Mt-I (PDB: 5TFV) and Mt-II (PDB ID 4YV5) retrieved from Protein Database (https://www.rcsb.org/).

We simulated the interaction in the enzymatic site of sPLA 2 s with palmitoyl phospholipids (head or complete structure) using AutoDock Vina software [119] . The predicted affinity between sPLA 2 s and palmitoyl phospholipids (head or complete) was similar ( Table 2) . Concerning to the interaction with the phospholipids head, Mt-I showed a higher affinity to POPC, POPE and POPS (-5.1, -4.7 and -5.0 kcal/mol, respectively) related to Mt-II. ( Table 2 ). When we simulated the docking with the complete palmitoyl phospholipid molecule, Mt-I also has a higher affinity than Mt-II ( Table 2) .

Although we do not observe a strong difference in the affinity between Mt-I and Mt-II for palmitoyl phospholipids, it is possible to note structural variation in the enzymatic site of these two toxins. Compared to Mt-II, the enzymatic site of Mt-I ( Figure 2A ) is more suitable due to a smaller aspartic acid radical group. The van der Waals radii volume of aspartic acid is 91 and hence it is more prominent, while the lysine has a volume of 135, and this results in less space in enzymatic site entrance in Mt-II ( Figure 2B) . This difference could create an enzymatic site more restricted to palmitoyl phospholipid entrance/binding and be partially responsible for the absence of enzymatic activity in Mt-II [120] . In addition, the enzymatic activity of Mt-I can be attributed to highly conserved catalytic site formed by the amino acid residues His48, Asp49, Tyr52 and Asp99. Asp49 coordinates the hydrolysis reaction of phospholipids together with the residues of the Ca2+ binding loop, essential in the catalytic activity of PLA 2 s. The substitution of lysine residue at the same position affects the ability of this protein to bind to Ca 2+, resulting in the absence of catalytic activity [92] .

Despite the stronger antiviral activity is associated with the enzymatic activity, the antiviral mechanism of sPLA 2 s does not depend exclusively on their catalytic site, since Lys49 sPLA 2 s and inhibited catalytically-active sPLA 2 s were also able to show antiviral effects, suggesting that sPLA 2 s may possess different mechanisms of action.

However, additional studies with different Lys49 from snake venom are required to better characterize the antiviral potential of this protein class.

Functional and structural studies have described that the activity of Lys49 PLA 2 s from snake venom toward cell membranes in myotoxic mechanism involves an allosteric transition, and the participation of two independent interaction sites with the target membrane [67, 72, [121] [122] [123] . The action of Lys49 PLA 2 s is related to a cluster of cationic and hydrophobic/aromatic amino acid residues located at the C-terminal region of this toxin. These two conserved regions in most Lys49-PLA 2 s are designed by -cationic membrane-docking site‖ (MDoS), which are formed by the strictly conserved C-terminal residues (Lys115 and Arg118), eventually aided by other cationic and exposed residues such as Lys20, Lys80, Lys122 and Lys127; and the -hydrophobic membrane-disruption site‖ (MDiS) formed by residues of Leu121 and Phe125. The key step for protein activation is the binding of a fatty acid at the hydrophobic channel, which leads to allosteric transition and structure stabilization exposing MDoS and MDiS to the membrane, following by the insertion of the MDiS region from both monomers into the target membrane. This penetration disrupts the lipid bilayer, causing alterations in the membrane permeability, highlighted by a prominent influx of ions (i.e., Ca 2+ and Na + ), and eventually, irreversible intracellular alterations and cell death [123] .

According to myotoxic mechanism of Lys49 PLA 2 s from viperid snake venoms, it is proposed that the fatty acids which are important to protein activation may come from membrane phospholipid hydrolysis by catalytic PLA 2 s (Asp49), highlighting the synergism between Asp49 PLA 2 s and Lys49 PLA 2 in snake envenomation [124] . In this way, the antiviral effects of the Lys49 PLA 2 s from snake venom, showed in this review, may be associated to fatty acids from the catalytic activity of cytosolic PLA 2 (cPLA 2 ) from virus lipid envelope, once it was demonstrated that enzymatic activity of the cPLA 2 is required for replication of various virus [125] [126] [127] . Muller and colleagues [126] showed that the pharmacological inhibition of a cellular phospholipase, cPLA 2 , using a specific small-molecule inhibitor, drastically reduces coronavirus RNA synthesis and, as a consequence, protein accumulation and the production of infectious J o u r n a l P r e -p r o o f virus progeny. In addition, cPLA 2 activity was shown to be critically involved in the production of infectious progeny of HCV and DENV [128] .

The present review highlighted that PLA 2 s from snake venom have become valuable as pharmacological tools and/or therapeutic approaches due to their extremely high specificity and potent activity against microbial infection. Regarding to antiviral properties, we highlighted the following remarks: (i) the antiviral effects of sPLA 2 s can be mediated by either a dependent or independent catalytic mechanism; (ii) sPLA 2 Journal Pre-proof J o u r n a l P r e -p r o o f 

Enteroviruses in the early 21st century: new manifestations and challenges

HPV-Related Disease, and the HPV Vaccine

Examining the promise of HIV elimination by 'test and treat' in hyperendemic settings

Herpes simplex: insights on pathogenesis and possible vaccines

Pamplona de Goes Cavalcanti, Zika virus outbreak in Brazil

Emergence and pandemic potential of swineorigin H1N1 influenza virus

Live Attenuated Yellow Fever 17D Vaccine: A Legacy Vaccine Still Controlling Outbreaks In Modern Day

The SARS-CoV-2 outbreak: What we know

Global rise in human infectious disease outbreaks

Viral host jumps: moving toward a predictive framework

The evolutionary history of vertebrate RNA viruses

Influenza: old and new threats

Emerging influenza viruses and the prospect of a universal influenza virus vaccine

Prediction of Number of Cases of 2019 Novel Coronavirus (COVID-19) Using Social Media Search Index

The global distribution and burden of dengue

Subversion and piracy: DNA viruses and immune evasion

Ebolavirus is internalized into host cells via macropinocytosis in a viral glycoprotein-dependent manner

Mechanisms of viral entry: sneaking in the front door

Dengue virus life cycle: viral and host factors modulating infectivity, Cellular and molecular life sciences

Challenges and responses in human vaccine development

The cost and challenge of vaccine development for emerging and emergent infectious diseases, The Lancet

The Signaling Pathways, and Therapeutic Targets of Antiviral Agents: Focusing on the Antiviral Approaches and Clinical Perspectives of Anthocyanins in the Management of Viral Diseases

Why are RNA virus mutation rates so damn high?

Overview of Direct-Acting Antiviral Drugs and Drug Resistance of Hepatitis C Virus

Influenza Polymerase Inhibitors: Mechanisms of Action and Resistance, Cold Spring Harbor perspectives in medicine

Adverse effects of antiretroviral therapy

Fulminant hepatic failure associated with 2',3'-dideoxyinosine (ddI)

Adverse effects of antiretroviral therapy for HIV infection

A historical overview of natural products in drug discovery

Natural Products in Drug Discovery: Impacts and Opportunities -An Assessment

Snake Venoms in Drug Discovery: Valuable Therapeutic Tools for Life Saving

The use of snake venom-derived compounds for new functional diagnostic test kits in the field of haemostasis

From snake venom toxins to therapeutics--cardiovascular examples

Antitumoral activity of snake venom proteins: new trends in cancer therapy

Angiotensin-converting enzyme inhibitors from the venom of Bothrops jararaca

Isolation, elucidation of structure, and synthesis

History of the design of captopril and related inhibitors of angiotensin converting enzyme

A GPIIb-IIIa-specific integrin antagonist from the venom of Sistrurus m. barbouri

Echistatin. A potent platelet aggregation inhibitor from the venom of the viper, Echis carinatus

Reptilase-R--a new reagent in blood coagulation

Defibrinogenating effect of batroxobin (Defibrase) in rats and inhibition of migration of human vascular smooth muscle cells by the plasma of batroxobin-treated rats in vitro

Isolation and characterization of moojenin, an acid-active, anticoagulant metalloproteinase from Bothrops moojeni venom

Aulogous fibrin sealant (Vivostat((R))) in the neurosurgical practice: Part II: Vertebro-spinal procedures

Snake Venom: From Deadly Toxins to Life-saving Therapeutics

Venom as a source of useful biologically active molecules, Emergency medicine (Fremantle

Toxins of Animal Venoms and Inhibitors: Molecular and Biotechnological Tools Useful to Human and Animal Health

Antiviral activity of animal venom peptides and related compounds, The journal of venomous animals and toxins including tropical diseases

Hypothesis of snake and insect venoms against Human Immunodeficiency Virus: a review

Phospholipase A2 biochemistry

Phospholipase Superfamily: Structure, Functions, and Biotechnological Applications

Phospholipases: an overview

Phospholipase A2--a structural review

Excitement ahead: structure, function and mechanism of snake venom phospholipase A2 enzymes

Insight into prostaglandin, leukotriene, and other eicosanoid functions using mice with targeted gene disruptions

Phospholipases A2: unveiling the secrets of a functionally versatile group of snake venom toxins

Minor snake venom proteins: Structure, function and potential applications

An in-depth snake venom proteopeptidome characterization: Benchmarking Bothrops jararaca

Proteomic profiling, functional characterization, and immunoneutralization of the venom of Porthidium porrasi, a pitviper endemic to Costa Rica

The phospholipase A2 superfamily and its group numbering system

The expanding superfamily of phospholipase A(2) enzymes: classification and characterization

A new class of phospholipases A2 with lysine in place of aspartate 49. Functional consequences for calcium and substrate binding

Biochemistry and toxicology of toxins purified from the venom of the snake Bothrops asper

Snake venom Lys49 myotoxins: From phospholipases A(2) to non-enzymatic membrane disruptors

N49 phospholipase A2, a unique subgroup of snake venom group II phospholipase A2

Asp-49 is not an absolute prerequisite for the enzymic activity of low-M(r) phospholipases A2: purification, characterization and computer modelling of an enzymically active Ser-49 phospholipase A2, ecarpholin S, from the venom of Echis carinatus sochureki (sawscaled viper

Lysine 49 phospholipase A2 proteins

A common cytolytic region in myotoxins, hemolysins, cardiotoxins and antibacterial peptides

Identification of the myotoxic site of the Lys49 phospholipase A(2) from Agkistrodon piscivorus piscivorus snake venom: synthetic C-terminal peptides from Lys49, but not from Asp49 myotoxins, exert membrane-damaging activities

A molecular mechanism for Lys49-phospholipase A2 activity based on ligand-induced conformational change

Synthetic peptides derived from the Cterminal region of Lys49 phospholipase A2 homologues from viperidae snake venoms: biomimetic activities and potential applications

Structural elements of secretory phospholipases A2 involved in the binding to M-type receptors

Targeting integrins for the control of tumour angiogenesis

Antitumor potential of Pllans-II, an acidic Asp49-PLA2 from Porthidium lansbergii lansbergii snake venom on human cervical carcinoma HeLa cells

Cell surface nucleolin interacts with and internalizes Bothrops asper Lys49 phospholipase A2 and mediates its toxic activity

A model to explain the pharmacological effects of snake venom phospholipases A2

Identification of the Molecular Determinants of the Antibacterial Activity of LmutTX, a Lys49 Phospholipase A2 Homologue Isolated from Lachesis muta muta Snake Venom (Linnaeus, 1766)

Antitumor potential of the myotoxin BthTX-I from Bothrops jararacussu snake venom: evaluation of cell cycle alterations and death mechanisms induced in tumor cell lines, The journal of venomous animals and toxins including tropical diseases

Human breast cancer cell death induced by BnSP-6, a Lys-49 PLA(2) homologue from Bothrops pauloensis venom

Antitumor and antimetastatic effects of PLA2-BthTX-II from Bothrops jararacussu venom on human breast cancer cells

MVL-PLA2, a phospholipase A2 from Macrovipera lebetina transmediterranea venom, inhibits tumor cells adhesion and migration

BnSP-7 toxin, a basic phospholipase A2 from Bothrops pauloensis snake venom, interferes with proliferation, ultrastructure and infectivity of Leishmania (Leishmania) amazonensis

Anti-parasitic effect on Toxoplasma gondii induced by BnSP-7, a Lys49-phospholipase A2 homologue from Bothrops pauloensis venom

The Anthelmintic Effect on Strongyloides venezuelensis

Homologue from Bothrops pauloensis Venom

Crotoxin and phospholipases A(2) from Crotalus durissus terrificus showed antiviral activity against dengue and yellow fever viruses

Phospholipase A2 isolated from the venom of Crotalus durissus terrificus inactivates dengue virus and other enveloped viruses by disrupting the viral envelope

Multiple effects of toxins isolated from Crotalus durissus terrificus on the hepatitis C virus life cycle

Molecular characterization of Lys49 and Asp49 phospholipases A₂ from snake venom and their antiviral activities against Dengue virus

Potent virucidal activity against Flaviviridae of a group IIA phospholipase A(2) isolated from the venom of Bothrops asper

Convulxin, a new toxin from the venom of the South American rattlesnake Crotalus durissus terrificus

Gyroxin, a toxin from the venom of Crotalus durissus terrificus, is a thrombin-like enzyme

Biological roles of the two components of crotoxin

Biochemistry and pharmacology of the crotoxin complex. I. Subfractionation and recombination of the crotoxin complex

Fosfolipasas A2 segregadas (sPLA2):¿amigas o enemigas? ¿Actores de la resistencia antibacteriana y antivirus de la inmunodeficiencia humana?

Bothropstoxin-I: amino acid sequence and function

Expression, purification and virucidal activity of two recombinant isoforms of phospholipase A2 from Crotalus durissus terrificus venom

The molecular and structural basis of advanced antiviral therapy for hepatitis C virus infection

Interaction of hepatitis C virus nonstructural protein 5A with core protein is critical for the production of infectious virus particles

Purification and partial characterization of two phospholipases A2 from Bothrops leucurus (white-tailedjararaca) snake venom

Discovery of novel [Arg49]phospholipase A2 isozymes from Protobothrops elegans venom and regional evolution of Crotalinae snake venom phospholipase A2 isozymes in the southwestern islands of Japan and Taiwan

Snake venomics of the lancehead pitviper Bothrops asper: geographic, individual, and ontogenetic variations

Bactericidal activity of Lys49 and Asp49 myotoxic phospholipases A2 from Bothrops asper snake venom--synthetic Lys49 myotoxin II-(115-129)-peptide identifies its bactericidal region

Interfacial enzymology: the secreted phospholipase A(2)-paradigm

Secreted phospholipases A(2), a new class of HIV inhibitors that block virus entry into host cells

Identification and properties the taipan venom

Both group IB and group IIA secreted phospholipases A2 are natural ligands of the mouse 180-kDa M-type receptor

Nigexine, a phospholipase A2 from cobra venom with cytotoxic properties not related to esterase activity. Purification, amino acid sequence, and biological properties

Receptors for a growing family of secreted phospholipases A2

Naja mossambica mossambica venom. Purification, some properties and the amino acid sequences of three phospholipases A (CM-I, CM-II and CM-III)

Purification and activation of phospholipase A2 isoforms from Naja mossambica mossambica (spitting cobra) venom

Broad-spectrum antiviral agents: secreted phospholipase A(2) targets viral envelope lipid bilayers derived from the endoplasmic reticulum membrane

Phospholipase A2 hydrolysis of supported phospholipid bilayers: a neutron reflectivity and ellipsometry study

Lipid map of the mammalian cell

Modeling Yeast Organelle Membranes and How Lipid Diversity Influences Bilayer Properties

The stem region of premembrane protein plays an important role in the virus surface protein rearrangement during dengue maturation

AutoDock Vina: improving the speed and accuracy of docking with a new scoring function, efficient optimization, and multithreading

A four-column theory for the origin of the genetic code: tracing the evolutionary pathways that gave rise to an optimized code

Neutralizing interaction between heparins and myotoxin II, a lysine 49 phospholipase A2 from Bothrops asper snake venom. Identification of a heparin-binding and cytolytic toxin region by the use of synthetic peptides and molecular modeling

Comparative structural studies on Lys49-phospholipases A(2) from Bothrops genus reveal their myotoxic site

A structure-based proposal for a comprehensive myotoxic mechanism of phospholipase A2-like proteins from viperid snake venoms

Synergism between basic Asp49 and Lys49 phospholipase A2 myotoxins of viperid snake venom in vitro and in vivo

Critical role of phospholipase A2 group IID in age-related susceptibility to severe acute respiratory syndrome-CoV infection

Inhibition of Cytosolic Phospholipase A(2)α Impairs an Early Step of Coronavirus Replication in Cell Culture

Human cytomegalovirus carries a cellderived phospholipase A2 required for infectivity

MAP-kinase regulated cytosolic phospholipase A2 activity is essential for production of infectious hepatitis C virus particles

Mt-II 50 g/mL DENV-1, 2, 3 50 g/mL YFV 2768 ng/mL (EC50) DENV-2

BthTX-I