Chemical Modifications of PhTX-I Myotoxin fromPorthidium hyoproraSnake Venom: Effects on Structural, Enzymatic, and Pharmacological Properties

Abstract

We recently described the isolation of a basic PLA2 (PhTX-I) from Porthidium hyoprora snake venom. This toxin exhibits high catalytic activity, induces in vivo myotoxicity, moderates footpad edema, and causes in vitro neuromuscular blockade. Here, we describe the chemical modifications of specific amino acid residues (His, Tyr, Lys, and Trp), performed in PhTX-I, to study their effects on the structural, enzymatic, and pharmacological properties of this myotoxin. After chemical treatment, a single His, 4 Tyr, 7 Lys, and one Trp residues were modified. The secondary structure of the protein remained unchanged as measured by circular dichroism; however other results indicated the critical role played by Lys and Tyr residues in myotoxic, neurotoxic activities and mainly in the cytotoxicity displayed by PhTX-I. His residue and therefore catalytic activity of PhTX-I are relevant for edematogenic, neurotoxic, and myotoxic effects, but not for its cytotoxic activity. This dissociation observed between enzymatic activity and some pharmacological effects suggests that other molecular regions distinct from the catalytic site may also play a role in the toxic activities exerted by this myotoxin. Our observations supported the hypothesis that both the catalytic sites as the hypothetical pharmacological sites are relevant to the pharmacological profile of PhTX-I.

Purification and partial characterization of an anticoagulant PLA2 from the venom of Indian Daboia russelii that induces inflammation through upregulation of proinflammatory mediators

“…Macrophages are involved in early response against inflammation and excessive production of proinflammatory mediators by these cells may lead to local tissue damage and systemic shock similar to a condition like endotoxin stimulation . Several reports have shown the impact of chemical modifications of His48 residue on the pharmacological effects of PLA 2 . The chemical modification of Asp49 PLA₂ isolated from B. asper venom was shown to markedly reduce the hyperalgesic effect .…”

PhTX-II a Basic Myotoxic Phospholipase A2 from Porthidium hyoprora Snake Venom, Pharmacological Characterization and Amino Acid Sequence by Mass Spectrometry

“…The His48 is in a key position since it participates in the PLA 2 active site as a catalytic residue [ 29 ], since the enzymatic activity of the PhTX-II was completely abolished after this modification, His48 was likely the residue modified, because this amino acid is part of the catalytic triad of this protein family. His-modified enzymes are suitable for both in vitro and in vivo systems in order to study the role of the enzymatic activity on the PLA 2 pharmacological profiles [ 11 , 35 , 36 ].…”

“…Incubation with BPB inhibited enzymatic activity of PhTX-II and dmarkedly decreased toxin-induced neuromuscular blockade (around 89%) in chick biventer cervicis preparations ( Figure 7 A) strengthening the hypothesis that phospholipid enzymatic hydrolysis is involved in this effect. Similarly, neurotoxic activity was inhibited almost completely after alkylation of His48 of Bbil-TX PLA 2 from Bothriopsis bilineata , Cdc-9 and Cdc-10 PLA 2 from ( Crotalus durissus cumanensis and PhTX-I from P. hyoprora [ 11 , 39 , 40 ].…”

“…In a previous work, we showed that P. hyoprora snake venom is a rich source of PLA 2 enzymes, and also, PhTX-I PLA 2 was purified and characterized [ 6 , 11 ]. In the present study, we expand on this pit viper by analyzing one novel myotoxic Asp49 PLA 2 (PhTX-II) isolated and sequenced by tandem mass spectrometry.…”

ACP-TX-I and ACP-TX-II, Two Novel Phospholipases A2 Isolated from Trans-Pecos Copperhead Agkistrodon contortrix pictigaster Venom: Biochemical and Functional Characterization

“…Since ACP-TX-II requires Ca 2+ for activity, chelators such as EDTA inhibited the enzymatic activity (Figure 4F). Histidine residue alkylation also abolished enzymatic activity of ACP-TX-II PLA 2 (Figure 4F), although alkylation does not completely disrupt the 3D structure of PLA 2 enzymes and their capacity to bind phospholipids, but it could modify their ability to interact with specific ligands or proteins [43].…”