Structure–Function Studies and Mechanism of Action of Snake Venom L-Amino Acid Oxidases

Abstract

Snake venom L-amino acid oxidases (SV-LAAOs) are the least studied venom enzymes. These enzymes catalyze the stereospecific oxidation of an L-amino acid to their corresponding a-keto acid with the liberation of hydrogen peroxide (H 2 O 2) and ammonia (NH 3). They display various pathological and physiological activities including induction of apoptosis, edema, platelet aggregation/inhibition, hemorrhagic, and anticoagulant activities. They also show antibacterial, antiviral and leishmanicidal activity and have been used as therapeutic agents in some disease conditions like cancer and anti-HIV drugs. Although the crystal structures of six SV-LAAOs are present in the Protein Data Bank (PDB), there is no single article that describes all of them in particular. To better understand their structural properties and correlate it with their function, the current work describes structure characterization, structure-based mechanism of catalysis, inhibition and substrate specificity of SV-LAAOs. Sequence analysis indicates a high sequence identity (>84%) among SV-LAAOs, comparatively lower sequence identity with Pig kidney D-amino acid oxidase (<50%) and very low sequence identity (<24%) with bacterial LAAOs, Fugal (L-lysine oxidase), and Zea mays Polyamine oxidase (PAAO). The three-dimensional structure of these enzymes are composed of three-domains, a FAD-binding domain, a substrate-binding domain and a helical domain. The sequence and structural analysis indicate that the amino acid residues in the loops vary in length and composition due to which the surface charge distribution also varies that may impart variable substrate specificity to these enzymes. The active site cavity volume and its average depth also vary in these enzymes. The inhibition of these enzymes by synthetic inhibitors will lead to the production of more potent antivenoms against snakebite envenomation.

The Sequence and Three-Dimensional Structure Characterization of Snake Venom Phospholipases B

“…On the other hand, PLBs of fungi, bacteria, and mammals have been shown to hydrolyze a broad range of substrates like phosphatidylcholine, phosphatidylinositol, phosphatidylserine, phosphatidylethanolamine, phosphatidic acid, lysophosphatidyl- choline, and lysophosphatidylethanolamine ( Supplementary Figure S8 ; Morgan et al, 2004 ; Lakomek et al, 2009 ; Repo et al, 2014 ). An explanation for the observed specificity of SVPLBs and PLBs from other organisms can be made on the basis of surface charge distribution around the active site cavity ( Ullah et al, 2018,2019 ; Ullah, 2020 ). In SVPLBs, the active site cavity is negatively charged, whereas the entry to the active site is positively charged ( Figure 3A ).…”

The Search for Natural and Synthetic Inhibitors That Would Complement Antivenoms as Therapeutics for Snakebite Envenoming

“…Snake venoms contain proteins which are widely present in species of the Elapidae, Viperidae and ‘Colubridae’ ( sensu lato ) families, but which do not exert a highly significant role in the overall toxicity of envenomings, although some may play ancillary roles. This is the case of L-amino acid oxidase, for which several functions have been described in addition to its enzymatic activity [ 93 ]. However, its role in envenoming has not been proven to be significant.…”

Snake Venoms in Diagnostic Hemostasis and Thrombosis

“…16 PLA 2 enzymes can induce platelet aggregation by releasing membrane arachidonic acid to form thromboxane A 2 , while other PLA 2 s inhibit aggregation via the cleavage products, or alter platelet morphology by disrupting the cytoskeleton. 16 Snake venom L-amino acid oxidases can either activate or inhibit platelets, 16,56 and 5′-nucleotidases inhibit platelet aggregation induced by adenosine diphosphate, sodium arachidonate, or collagen. 16,57 Diagnostic platelet function testing involves in vitro platelet activation with a panel of agonists employing different mechanisms, to discern specific abnormalities.…”