Heterodimeric V. nikolskii phospholipases A2 induce aggregation of the lipid bilayer

Estimation of the Phospholipase A2 Selectivity on POPC/POPG Membranes Using the Interaction Map

Abstract

The regulation of the activity and selectivity of phospholipase A2 (PLA2), which is capable of cleaving fatty acid in the second position (sn-2) of the phospholipid, is carried out through the membrane-binding and catalytic sites of the enzyme. For hydrolytic activity, PLA2 must first bind to the phospholipid membrane, and the binding efficiency depends on the composition of the membrane. The membrane-binding site of PLA2 is formed by several tens of amino acids and its composition differs from enzyme to enzyme; hydrophobic and positively charged amino acids play a key role in the interaction. In this work, we investigated the interaction of PLA2 from bee venom with phospholipid bilayers of palmitoyl oleoylphosphatidylcholine (POPC) containing different amounts of palmitoyloleoylphosphatidylglycerol (POPG). On the basis of the measurements of the protein intrinsic fluorescence and the anisotropy of the fluorescence of the lipid probe we propose the construction of lipid–protein interaction maps, which reflect both the efficiency of protein binding and changes in the structure of the membrane. These changes cause alterations in the fluorescence anisotropy of the label, which in turn is a measure of the mobility of the lipid environment of the fluorescent probe. Analysis of interaction maps showed that there is a relationship between lipid mobility and enzyme binding efficiency: the optimum interaction of PLA2 with membranes from a POPC/POPG mixture lies in the region of the highest lipid mobility, and not in the region of the highest negative charge. This dependence complements the existing understanding of the process of recognition of the membrane surface by the enzyme and the selection of lipids by the enzyme already bound to the membrane. The proposed mapping method can be extended to other membrane-active proteins.

Venom-Induced Blood Disturbances by Palearctic Viperid Snakes, and Their Relative Neutralization by Antivenoms and Enzyme-Inhibitors

Palearctic vipers are medically significant snakes in the genera Daboia, Macrovipera, Montivipera, and Vipera which occur throughout Europe, Central Asia, Near and Middle East. While the ancestral condition is that of a small-bodied, lowland species, extensive diversification has occurred in body size, and niche specialization. Using 27 venom samples and a panel of in vitro coagulation assays, we evaluated the relative coagulotoxic potency of Palearctic viper venoms and compared their neutralization by three antivenoms (Insoserp Europe, VIPERFAV and ViperaTAb) and two metalloprotease inhibitors (prinomastat and DMPS). We show that variation in morphology parallels variation in the Factor X activating procoagulant toxicity, with the three convergent evolutions of larger body sizes (Daboia genus, Macrovipera genus, and Vipera ammodytes uniquely within the Vipera genus) were each accompanied by a significant increase in procoagulant potency. In contrast, the two convergent evolutions of high altitude specialization (the Montivipera genus and Vipera latastei uniquely within the Vipera genus) were each accompanied by a shift away from procoagulant action, with the Montivipera species being particularly potently anticoagulant. Inoserp Europe and VIPERFAV antivenoms were both effective against a broad range of Vipera species, with Inoserp able to neutralize additional species relative to VIPERFAV, reflective of its more complex antivenom immunization mixture. In contrast, ViperaTAb was extremely potent in neutralizing V. berus but, reflective of this being a monovalent antivenom, it was not effective against other Vipera species. The enzyme inhibitor prinomastat efficiently neutralized the metalloprotease-driven Factor X activation of the procoagulant venoms. In contrast, DMPS (2,3-dimercapto-1-propanesulfonic acid), which as been suggested as another potential treatment option in the absence of antivenom, DMPS failed against all venoms tested. Overall, our results highlight the evolutionary variations within Palearctic vipers and help to inform clinical management of viper envenomation.

Snake venom phospholipase A2s exhibit strong virucidal activity against SARS-CoV-2 and inhibit the viral spike glycoprotein interaction with ACE2

The COVID-19 pandemic caused by SARS-CoV-2 requires new treatments both to alleviate the symptoms and to prevent the spread of this disease. Previous studies demonstrated good antiviral and virucidal activity of phospholipase A₂s (PLA₂s) from snake venoms against viruses from different families but there was no data for coronaviruses. Here we show that PLA₂s from snake venoms protect Vero E6 cells against SARS-CoV-2 cytopathic effects. PLA₂s showed low cytotoxicity to Vero E6 cells with some activity at micromolar concentrations, but strong antiviral activity at nanomolar concentrations. Dimeric PLA₂ from the viper Vipera nikolskii and its subunits manifested especially potent virucidal effects, which were related to their phospholipolytic activity, and inhibited cell-cell fusion mediated by the SARS-CoV-2 spike glycoprotein. Moreover, PLA₂s interfered with binding both of an antibody against ACE2 and of the receptor-binding domain of the glycoprotein S to 293T/ACE2 cells. This is the first demonstration of a detrimental effect of PLA₂s on β-coronaviruses. Thus, snake PLA₂s are promising for the development of antiviral drugs that target the viral envelope, and could also prove to be useful tools to study the interaction of viruses with host cells.

Phospholipase A2 way to hydrolysis: Dint formation, hydrophobic mismatch, and lipid exclusion

Phospholipase A2 (PLA2) exerts a wide range of biological effects and attracts a lot of attention of researchers. Two sites are involved in manifestation of PLA2 enzymatic activity: catalytic site responsible for substrate binding and fatty acid cleavage from the sn-2 position of a glycerophospholipid, and interface binding site (IBS) responsible for the protein binding to lipid membrane. IBS is formed by positively charged and hydrophobic amino acids on the outer surface of the protein molecule. Understanding the mechanism of PLA2 interaction with the lipid membrane is the most challenging step in biochemistry of this enzyme. We used a combination of experimental and computer simulation techniques to clarify molecular details of bee venom PLA2 interaction with lipid bilayers formed by palmitoyloleoylphosphatidylcholine or dipalmitoylphosphatidylcholine. We found that after initial enzyme contact with the membrane, a network of hydrogen bonds was formed. This led to deformation of the interacting leaflet and dint formation. The bilayer response to the deformation depended on its phase state. In a gel-phase bilayer, diffusion of lipids is restricted therefore chain melting occurred in both leaflets of the bilayer. In the case of a fluid-phase bilayer, lateral diffusion is possible, and lipid polar head groups were excluded from the contact area. As a result, the bilayer became thinner and a large hydrophobic area was formed. We assume that relative ability of a bilayer to come through lipid redistribution process defines the rate of initial stages of the catalysis.