Molecular cloning and structural modelling of gamma-phospholipase A2 inhibitors from Bothrops atrox and Micrurus lemniscatus snakes

Hyperglycosylation impairs the inhibitory activity of rCdtPLI2, the first recombinant beta-phospholipase A2 inhibitor

Crotoxin, a phospholipase A2 (PLA2) complex and the major Crotalus venom component, is responsible for the main symptoms described in crotalic snakebite envenomings and a key target for PLA2 inhibitors (PLIs). PLIs comprise the alpha, beta and gamma families, and, due to a lack of reports on beta-PLIs, this study aimed to heterologously express CdtPLI2 from Crotalus durissus terrificus venom gland to improve the knowledge of the neglected beta-PLI family. Thereby, recombinant CdtPLI2 (rCdtPLI2) was produced in the eukaryotic Pichia pastoris system to keep some native post-translational modifications. rCdtPLI2 (~41 kDa) presents both N- and O-linked glycans. Alpha-mannosidase digested-rCdtPLI2 (1 mol) strongly inhibited (73%) CB-Cdc catalytic activity (5 moles), demonstrating that glycosylations performed by P. pastoris affect rCdtPLI2 action. Digested-rCdtPLI2 also inhibited PLA2s from diverse Brazilian snake venoms. Furthermore, rCdtPLI2 (1 mol) abolished the catalytic activity of Lmr-PLA2 (5 moles) and reduced the CTx-Cdc (5 moles) enzyme activity by 65%, suppressing basic and acidic snake venom PLA2s. Additionally, crotalic antivenom did not recognize rCdtPLI2, suggesting a lack of neutralization by antivenom antibodies. These findings demonstrate that studying snake venom components may reveal interesting novel molecules to be studied in the snakebite treatment and help to understand these underexplored inhibitors.

Mapping possible interaction sites for crotoxin in CNF, a gamma PLA2 inhibitor from Crotalus durissus terrificus rattle snake, using SPOT synthesis

Phospholipases A2 (PLA2s) are main components of snake venoms. Several snake species possess endogenous PLA2 inhibitors in their circulating blood, which are generally known as sbPLIs (an acronym for snake blood phospholipase A2inhibitors). The sbPLIs are categorized in three classes (alpha, beta or gamma) depending on the existence of distinguishing protein domains in their structure. The Crotalus durrissus terrificus venom has a highly neurotoxic PLA2 - crotoxin (CTX) - in its composition and the self-protection of the snake is mainly ensured by a sbγPLI named CNF (standing for Crotalusneutralizing factor). In an attempt to find smaller molecules able to inhibit the catalytic activity of CTX, in the present study we used linear peptide arrays to identify CNF segments possibly involved in the interaction with the toxin. Five reacting segments were identified as possible interacting regions. The target peptides were synthesized and located in the in silico CNF structure. Although all of them are exposed to the solvent, high concentrations were needed to inhibit the PLA2 activity of the whole venom or CTX. Limitations of the methodology employed and particular characteristics of CTX inhibition by CNF are discussed.

Identification and characterization of the first endogenous phospholipase A2 inhibitor from a non-venomous tropical snake, Boa constrictor (Serpentes: Boidae)

Background

Endogenous phospholipase A₂ inhibitors from snake blood (sbPLIs) have been isolated from several species around the world, with the primary function of self-protection against the action of toxic phospholipases A_2. In American snakes, sbPLIs were solely described in pit vipers, in which the natural protection role is justified. In this study, we described a sbPLI in Boa constrictor (popularly known as jiboia), a non-venomous snake species from America.

Methods

PLA₂ inhibitory activity was tested in the blood plasma of B. constrictor using C. d. terrificus venom as the enzyme source. Antibodies developed against CNF, a sbγPLI from Crotalus durissus terrificus, were used to investigate the presence of homologues in the blood plasma of B. constrictor. A CNF-like molecule with a PLA₂ inhibitory activity was purified by column chromatography. The encoding gene for the inhibitor was cloned from B. constrictor liver tissue. The DNA fragment was cloned, purified and sequenced. The deduced primary sequence of interest was aligned with known sbγPLIs from the literature.

Results

The blood plasma of B. constrictor displayed PLA₂ inhibitory activity. A CNF-like molecule (named BcNF) was identified and purified from the blood plasma of B. constrictor. Basic properties such as molecular mass, composing amino acids, and pI were comparable, but BcNF displayed reduced specific activity in PLA₂ inhibition. BcNF showed highest identity scores (ISs) with sbγPLIs from pit vipers from Latin America (90-100%), followed by gamma inhibitors from Asian viperid (80-90%). ISs below 70% were obtained for BcNF and non-venomous species from Asia.

Conclusion

A functional sbγPLI (BcNF) was described in the blood plasma of B. constrictor. BcNF displayed higher primary identity with sbγPLIs from Viperidae than to sbγPLIs from non-venomous species from Asia. The physiological role played by sbγPLIs in non-venomous snake species remains to be understood. Further investigation is needed.

Antimyotoxic Activity of Synthetic Peptides Derived from Bothrops atrox Snake Gamma Phospholipase A2 Inhibitor Selected by Virtual Screening

Background:

Several studies have aimed to identify molecules that inhibit the toxic actions of snake venom phospholipases A2 (PLA2s). Studies carried out with PLA2 inhibitors (PLIs) have been shown to be efficient in this assignment.

Objective:

This work aimed to analyze the interaction of peptides derived from Bothrops atrox PLIγ (atPLIγ) with a PLA2 and to evaluate the ability of these peptides to reduce phospholipase and myotoxic activities.

Methods:

Peptides were subjected to molecular docking with a homologous Lys49 PLA2 from B. atrox venom modeled by homology. Phospholipase activity neutralization assay was performed with BthTX-II and different ratios of the peptides. A catalytically active and an inactive PLA2 were purified from the B. atrox venom and used together in the in vitro myotoxic activity neutralization experiments with the peptides.

Results:

The peptides interacted with amino acids near the PLA2 hydrophobic channel and the loop that would be bound to calcium in Asp49 PLA2. They were able to reduce phospholipase activity and peptides DFCHNV and ATHEE reached the highest reduction levels, being these two peptides the best that also interacted in the in silico experiments. The peptides reduced the myotubes cell damage with a highlight for the DFCHNV peptide, which reduced by about 65%. It has been suggested that myotoxic activity reduction is related to the sites occupied in the PLA2 structure, which could corroborate the results observed in molecular docking.

Conclusion:

This study should contribute to the investigation of the potential of PLIs to inhibit the toxic effects of PLA2s.

Purification and characterization of the first γ-phospholipase inhibitor (γPLI) from Bothrops jararaca snake serum

Phospholipases A₂ (PLA₂) are enzymes acting on the cell membrane phospholipids resulting in fatty acids and lysophospholipids and deconstructing the cell membrane. This protein is commonly found in snake venoms, causing tissue inflammation in the affected area. Evidence indicates that snakes have natural resistance to their own venom due to protective properties in plasma, that inhibit the action of proteins present in their venom. Given that, this study aimed to purify and characterize a γPLI from Bothrops jararaca serum, named γBjPLI. PLA₂ inhibitor was isolated using two chromatographic steps: an ion exchange column (DEAE), followed by an affinity column (crotoxin coupled to a CNBr-activated Sepharose resin). The purity and biochemical characterization of the isolated protein were analyzed by RP-HPLC, SEC, SDS-PAGE, circular dichroism and mass spectrometry. The ability to inhibit PLA₂ was determined by enzymatic activity, neutralization of paw edema and myonecrosis. The protein purity was confirmed by RP-HPLC and SEC, whilst an apparent molecular mass of 25 kDa and 20 kDa was obtained by SDS-PAGE, under reducing and non-reducing conditions, respectively. According to mass spectrometry analysis, this protein showed 72% and 68% of coverage when aligned to amino acid sequences of two proteins already described as PLIs. Thus, the inhibitory activity of enzymatic, edema and myonecrotic activities by γBjPLI suggests a role of this inhibitor for protection of these snakes against self-envenomation.