Basic phospholipase A2 homolog bothropstoxin-II

UniProtKB accession:  P45881

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UniProtKB description:  Snake venom phospholipase A2 (PLA2) that shows low enzymatic activity even tough it conserves the catalytic residues (PubMed:9619591). Shows a strong myotoxic activity and induces indirect hemolysis, anticoagulant properties, and cytotoxic activities (PubMed:11018293). In vivo, it induces muscle necrosis, accompanied by polymorphonuclear cell infiltration, and edema in the mouse paw (PubMed:1660822, PubMed:11018293). It exerts its function even in the absence of extracellular calcium, indicating it is not a calcium-dependent enzyme (PubMed:20878713). A model of myotoxic mechanism has been proposed: an apo Lys49-PLA2 is activated by the entrance of a hydrophobic molecule (e.g. fatty acid) at the hydrophobic channel of the protein leading to a reorientation of a monomer (By similarity). This reorientation causes a transition between 'inactive' to 'active' states, causing alignment of C-terminal and membrane-docking sites (MDoS) side-by-side and putting the membrane-disruption sites (MDiS) in the same plane, exposed to solvent and in a symmetric position for both monomers (By similarity). The MDoS region stabilizes the toxin on membrane by the interaction of charged residues with phospholipid head groups (By similarity). Subsequently, the MDiS region destabilizes the membrane with penetration of hydrophobic residues (By similarity). This insertion causes a disorganization of the membrane, allowing an uncontrolled influx of ions (i.e. calcium and sodium), and eventually triggering irreversible intracellular alterations and cell death (By similarity).