title: Effects of chemical modifications of Pa-11, a phospholipase A2 from the venom of Australian king brown snake (Pseudechis australis), on its biological activities.
abstract: Pa-11, a phospholipase A2 isolated from the venom of an Australian elapid snake Pseudechis australis, was chemically modified and its enzymic, neuromuscular and lethal activities were studied. Carboxymethylation of Met-8 gave a derivative with 2% of the enzymic activity and less than 3% of the lethal activity of native Pa-11; it had about 5% of the original ability to block directly and indirectly stimulated mouse phrenic nerve-hemidiaphragm preparations. Nitrophenylsulfenylation of tryptophanyl residues at positions 31 and 69 caused loss of all activities. Amidination of all 14 lysyl residues gave a derivative with 41% and 16% of the enzymic and lethal activities, respectively, but with less than 5% of the original neuromuscular blocking activity. Mono-carbamoylation of lysyl residues at positions 58, 63, 81 and 85 was achieved. The most abundant derivative, 58-carbamoyl-lysine Pa-11 was enzymically 130% and lethally 100% as active as native Pa-11, but it had only about 20% of the native's neuromuscular activity in vitro. 63-Carbamoyl-lysine Pa-11 had 10% of the enzymic and 20% of the lethal activities, respectively; however, it retained at least 50% of its ability to block neuromuscular transmission in vitro, while losing most of its activity to block directly stimulated muscle contractions. 81- and 85-Carbamoyl derivatives have the same enzymic and lethal activities as the original protein, but the 85 derivative had less than 10% of the native neuromuscular activity. Hence, modifications of lysine residues at positions 58, 63 and 85 seem to be particularly significant in altering the neuromuscular, but not enzymic, activity of Pa-11, perhaps by altering the ability of the toxin to bind to its target on nerve and muscle membranes. Modification at position 63 appeared to lead to a dissociation of effects on neuromuscular transmission and directly on muscle cells.
authors.affiliation: Department of Chemistry, Faculty of Science, Tohoku University, Sendai, Japan.
authors.forename: C
authors.initials: C
authors.lastname: Takasaki
authors.forename: A
authors.initials: A
authors.lastname: Sugama
authors.forename: A
authors.initials: A
authors.lastname: Yanagita
authors.forename: N
authors.initials: N
authors.lastname: Tamiya
authors.forename: E G
authors.initials: EG
authors.lastname: Rowan
authors.forename: A L
authors.initials: AL
authors.lastname: Harvey
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003964:Diaphragm / Q000187:drug effects; D004546:Elapid Venoms / Q000032:analysis* / Q000633:toxicity; D006632:Histamine / Q000032:analysis; D008239:Lysine / Q000032:analysis; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D009469:Neuromuscular Junction / Q000187:drug effects; D010740:Phospholipases / Q000032:analysis*; D010741:Phospholipases A / Q000032:analysis* / Q000633:toxicity; D054467:Phospholipases A2; D010791:Phrenic Nerve / Q000187:drug effects; D014364:Tryptophan / Q000032:analysis
chemical_list: D004546:Elapid Venoms; C026235:Pseudechis venom; D006632:Histamine; D014364:Tryptophan; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2; D008239:Lysine