Structure–function relationships in the neurotoxin Vipoxin from the venom of Vipera ammodytes meridionalis

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• 作者：Georgieva ; Dessislava Nikolova ; Genov ; Nicolay ; Nikolov ; Peter ; Aleksiev ; Boris ; Rajashankar ; Kanagalaghatta R. ; et. al.
• 关键词：Snake venom ; Phospholipase A₂ ; Toxicity ; PLA₂ ; phospholipase A₂ ; Inh ; inhibitor ; ASA ; accessible surface area ; P and I in the numbering system for tyrosines and tryptophans mean PLA₂ and Inh components of Vipoxi
• 刊名：Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
• 出版年：2003
• 出版时间：February, 2003
• 年：2003
• 卷：59
• 期：3
• 页码：617-627
• 全文大小：302 K

文摘

The neurotoxic complex Vipoxin is the lethal component of the venom of Vipera ammodytes meridionalis, the most toxic snake in Europe. It is a complex between a toxic phospholipase A₂ (PLA₂) and a non-toxic and catalytically inactive protein, stabilizing the enzyme and reducing the activity and toxicity. Structure–function relationships in this complex were studied by spectroscopic methods. A good correlation between the ionization behaviour and accessible surface area (ASA) of the tyrosyl residues was observed. In the toxic PLA₂ subunit phenolic groups participate in H-bonding network that stabilizes the catalytically and pharmacologically active conformation. The tryptophan fluorescence decay of Vipoxin is well fitted by two exponentials with lifetimes of 0.1 (54 % ) and 2.5 (46 % ) ns. W20P, W31P and W31I are located in the interface between the two subunits and participate in hydrophobic interactions stabilizing the complex. Dissociation of the complex leads to a transition of the tryptophans from hydrophobic to hydrophilic environment, which influences mainly τ₂. The longer lifetime is more sensitive to the polarity of the environment. Circular dichroism measurements demonstrate that the two components of the neurotoxin preserve their secondary structure after dissociation of the complex. The results of the spectroscopic studies are in accordance with a mechanism of blockade of transmission across the neuromuscular junctions of the breathing muscles by interaction of a dissociated toxic PLA₂ with a membrane. The loss of toxicity is connected with slight changes in the secondary structure of PLA₂. CD studies also show a substantial contribution of disulfide bonds to the stability of the neurotoxic complex and its components.