Snake Cytotoxins Bind to Membranes via Interactions with Phosphatidylserine Head Groups of Lipids

Abstract

The major representatives of Elapidae snake venom, cytotoxins (CTs), share similar three-fingered fold and exert diverse range of biological activities against various cell types. CT-induced cell death starts from the membrane recognition process, whose molecular details remain unclear. It is known, however, that the presence of anionic lipids in cell membranes is one of the important factors determining CT-membrane binding. In this work, we therefore investigated specific interactions between one of the most abundant of such lipids, phosphatidylserine (PS), and CT 4 of Naja kaouthia using a combined, experimental and modeling, approach. It was shown that incorporation of PS into zwitterionic liposomes greatly increased the membrane-damaging activity of CT 4 measured by the release of the liposome-entrapped calcein fluorescent dye. The CT-induced leakage rate depends on the PS concentration with a maximum at approximately 20% PS. Interestingly, the effects observed for PS were much more pronounced than those measured for another anionic lipid, sulfatide. To delineate the potential PS binding sites on CT 4 and estimate their relative affinities, a series of computer simulations was performed for the systems containing the head group of PS and different spatial models of CT 4 in aqueous solution and in an implicit membrane. This was done using an original hybrid computational protocol implementing docking, Monte Carlo and molecular dynamics simulations. As a result, at least three putative PS-binding sites with different affinities to PS molecule were delineated. Being located in different parts of the CT molecule, these anion-binding sites can potentially facilitate and modulate the multi-step process of the toxin insertion into lipid bilayers. This feature together with the diverse binding affinities of the sites to a wide variety of anionic targets on the membrane surface appears to be functionally meaningful and may adjust CT action against different types of cells.

Comparative venom gland transcriptomics ofNaja kaouthia(monocled cobra) from Malaysia and Thailand: elucidating geographical venom variation and insights into sequence novelty

“…Structurally resembling the SNTXs, CTXs are basic proteins with hydrophobic three-finger loops that can interact with the phospholipid bilayer of cell membranes, thereby mediating cytotoxic effect (Feofanov et al, 2005; Konshina et al, 2011; Osipov et al, 2008; Tan & Tan, 2016). CTX genes are highly expressed in N. kaouthia venom glands, with transcripts constituting 28.99% and 20.52% of the total toxin FPKM in NK-M and NK-T, respectively.…”

Protective effects of melatonin against oxidative damage induced by Egyptian cobra (Naja haje) crude venom in rats

“…This variability may be due to the fact that snake venoms contain various enzymes and toxic proteins that represent the most sophisticated integrated weapons systems in the natural world (Fry, 2005). Moreover, there are marked differences in the effects of different cytotoxins on various mammalian cell types (Konshina et al, 2011). The complexity of in vivo systems often makes it difficult to interpret effects measured at the molecular level.…”

Snake Venom Cytotoxins, Phospholipase A2s, and Zn2+-dependent Metalloproteinases: Mechanisms of Action and Pharmacological Relevance

“…The mechanisms for cytotoxin-mediated toxicity include modulating the activity of membrane-bound enzymes, depolarizing excitable membranes of heart cells and of neurons, inhibiting platelet aggregation, inducing hemolysis and cytotoxicity, and bringing about cardiac arrest [12,42,43]. It is widely accepted that most pathological activities of cytotoxins are based on their ability to bind to cell membranes leading to alterations in the organization and function of lipid bilayers [2,10,12,14,29,44]. Snake envenomation due to Naja species is highly prevalent in Africa and mortality is often associated with the potent necrotic activity of Naja -derived cytotoxins.…”

“…The inhibition of protein kinase C (PKC) by cytotoxins is a consequence of the association of cytotoxins to a site on PS that is required for the association and activation of PKC [74]. A recent study that used computer simulations to study the interaction between N. kaouthia cytotoxin and PS suggest that cytotoxins contain several PS-binding sites [10]. These binding sites have a strong ability to accommodate low molecular weight compounds (like the head group of PS) in a variety of different conformations [10].…”

“…The major types of biomolecules found in snake venom are proteins, some of which are enzymes whereas other proteins lack catalytic activity. The most potent toxins of snake venom, which are responsible for causing severe pathophysiological effects after envenomation, are α-neurotoxins – non-enzymatic nAChRs binding proteins [5,6], β-neurotoxins – pre-synaptic phospholipase A2 (PLA2) [7–9] and pre-synaptic phospholipase A 2 (PLA 2 ), β-neurotoxins [7–9], cytotoxins [10–16] non-neurotoxic PLA 2 s [17–20], and Zn 2+ -dependent metalloproteinases [21]. All of these toxins will be briefly reviewed in this section and more extensively in the ensuing sections of this review.…”