title: Naja naja oxiana Cobra Venom Cytotoxins CTI and CTII Disrupt Mitochondrial Membrane Integrity: Implications for Basic Three-Fingered Cytotoxins.
abstract: Cobra venom cytotoxins are basic three-fingered, amphipathic, non-enzymatic proteins that constitute a major fraction of cobra venom. While cytotoxins cause mitochondrial dysfunction in different cell types, the mechanisms by which cytotoxins bind to mitochondria remain unknown. We analyzed the abilities of CTI and CTII, S-type and P-type cytotoxins from Naja naja oxiana respectively, to associate with isolated mitochondrial fractions or with model membranes that simulate the mitochondrial lipid environment by using a myriad of biophysical techniques. Phosphorus-31 nuclear magnetic resonance (31P-NMR) spectroscopy data suggest that both cytotoxins bind to isolated mitochondrial fractions and promote the formation of aberrant non-bilayer structures. We then hypothesized that CTI and CTII bind to cardiolipin (CL) to disrupt mitochondrial membranes. Collectively, 31P-NMR, electron paramagnetic resonance (EPR), proton NMR (1H-NMR), deuterium NMR (2H-NMR) spectroscopy, differential scanning calorimetry, and erythrosine phosphorescence assays suggest that CTI and CTII bind to CL to generate non-bilayer structures and promote the permeabilization, dehydration and fusion of large unilamellar phosphatidylcholine (PC) liposomes enriched with CL. On the other hand, CTII but not CTI caused biophysical alterations of large unilamellar PC liposomes enriched with phosphatidylserine (PS). Mechanistically, single molecule docking simulations identified putative CL, PS and PC binding sites in CTI and CTII. While the predicted binding sites for PS and PC share a high number of interactive amino acid residues in CTI and CTII, the CL biding sites in CTII and CTI are more divergent as it contains additional interactive amino acid residues. Overall, our data suggest that cytotoxins physically associate with mitochondrial membranes by binding to CL to disrupt mitochondrial structural integrity.
authors.affiliation: Applied Mathematics and Informatics Department, Moscow State University Branch, Tashkent, Uzbekistan; Science Department, Tashkent Ulugbek International School, Tashkent, Uzbekistan.
authors.forename: Sardar E
authors.initials: SE
authors.lastname: Gasanov
authors.affiliation: Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America.
authors.forename: Indira H
authors.initials: IH
authors.lastname: Shrivastava
authors.affiliation: Applied Mathematics and Informatics Department, Moscow State University Branch, Tashkent, Uzbekistan.
authors.forename: Firuz S
authors.initials: FS
authors.lastname: Israilov
authors.affiliation: Applied Mathematics and Informatics Department, Moscow State University Branch, Tashkent, Uzbekistan.
authors.forename: Aleksandr A
authors.initials: AA
authors.lastname: Kim
authors.affiliation: Applied Mathematics and Informatics Department, Moscow State University Branch, Tashkent, Uzbekistan.
authors.forename: Kamila A
authors.initials: KA
authors.lastname: Rylova
authors.affiliation: Department of Pharmacology, University of Nevada School of Medicine, Reno, Nevada, United States of America.
authors.forename: Boris
authors.initials: B
authors.lastname: Zhang
authors.affiliation: Department of Pharmacology, University of Nevada School of Medicine, Reno, Nevada, United States of America.
authors.forename: Ruben K
authors.initials: RK
authors.lastname: Dagda
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002308:Cardiolipins / Q000737:chemistry / Q000378:metabolism; D003603:Cytotoxins / Q000737:chemistry* / Q000378:metabolism / Q000633:toxicity*; D004546:Elapid Venoms / Q000737:chemistry*; D008051:Lipid Bilayers; D051336:Mitochondrial Membranes / Q000187:drug effects*; D008958:Models, Molecular; D062105:Molecular Docking Simulation; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D016415:Sequence Alignment; D053835:Unilamellar Liposomes
chemical_list: D002308:Cardiolipins; D003603:Cytotoxins; D004546:Elapid Venoms; D008051:Lipid Bilayers; D053835:Unilamellar Liposomes