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.
Highlights
One of characteristic features of cytotoxins (CTs) from snake venom is their ability to lyse different types of cells like erythrocytes, epithelial and certain lines of tumor cells [1,2,3]
In accordance with the previously obtained data concerning the interactions of CT A3 with model lipid membranes [6,7], CT 4 caused no detectable lytic effect on pure POPC vesicles, whereas introduction of an acidic lipid into the model membrane led to a noticeable toxin-induced calcein release
It is interesting to note that such a modest ability of CT 4 to induce leakage of the POPC/SGC5% liposomes contradicts the fluorescence data reported earlier for CT A3 [7]
Summary
One of characteristic features of cytotoxins (CTs) from snake venom is their ability to lyse different types of cells like erythrocytes, epithelial and certain lines of tumor cells [1,2,3]. CTs are highly basic b-sheet proteins with molecular weight of about 6.5 kDa. All CTs have similar three-dimensional (3D) structures adopting a three-fingered loop-folding topology stabilized by four disulfide bonds. All CTs have similar three-dimensional (3D) structures adopting a three-fingered loop-folding topology stabilized by four disulfide bonds These proteins manifest strong amphiphilic properties on their molecular surface: apolar tips of loops I-III form a hydrophobic zone flanked by a positively charged ‘‘belt’’ composed of the conservative Lys and Arg residues. Experiments on model membranes [4,5] have demonstrated that the hydrophobic ‘‘bottom’’ represents a principal membrane-binding motif of CTs. Structural defects in lipid bilayer induced by CT binding to membrane have been demonstrated to lead to formation of the pore, whose size and life time have been estimated [6,7]. Despite the well-documented membranelytic activity and intensive studies of CTs (see [2] for review), exact molecular mechanisms of CT-induced cell damage are still unknown
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
