Modeling of acanthoxin A1, a PLA2 enzyme from the venom of the common death adder (Acanthophis antarcticus)

Structural analysis of a group III Glu62-phospholipase A2 from the scorpion, Mesobuthus tamulus: Targeting and reversible inhibition by native peptides

Group III phospholipase A(2) enzyme transcript from the Mesobuthus tamulus (Indian red scorpion) codes for three distinct products that include a large enzymatic subunit, a pentameric peptide and a small non-enzymatic subunit. The structures of these two subunits were modeled based on their sequence identity to bee venom PLA(2) and the partial sequence of MU2 adaptin subunit of AP2 clathrin adaptor, respectively. The enzymatic subunit comprises of three helices, the calcium binding loop and a substrate binding hydrophobic channel where the structure is stabilized by four disulfide bonds. The active site of the enzyme shows a catalytic histidine residue. Interestingly, there is a conservative mutation of the conserved aspartic acid, a classical participant of catalysis in this enzyme family, to glutamic acid. However, the side chain oxygen atoms of this glutamate are oriented away from the catalytic histidine implicating the non-participation of this residue in stabilizing the tautomeric conformation of the histidine. The acidic non-enzymatic subunit comprises of extensive hydrophobic residues with a conformation of an anti-parallel β-sheets making it ideal for tissue specific targeting. The native pentapeptide with the sequence Alanine-Arginine-Serine-Alanine-Arginine was docked to the enzymatic subunit. The peptide ligand occupies the hydrophobic cavity and makes a plethora of interactions with the residues in the channel, including a hydrogen bond with the crucial catalytic histidine and coordinate bond with the calcium ion. This ligand has a binding constant (K(D)) of 1.5μM. This makes the ligand a potential reversible inhibitor, ideal to prevent the enzyme from interacting with non-specific molecules enroute to the target. The enzyme-ligand complex also provides a model to understand the stereochemistry required for the design of more potent drug molecules against such enzyme drug targets.

Snake venoms and their toxins: An Australian perspective

Australia is home to a vast collection of highly venomous terrestrial and marine snakes. As such, Australia has proven to be an excellent source of investigative material for both local and international toxinologists. Research on snake venoms initially focussed on identifying the most lethal species, and the venom components responsible for the lethality, so that treatment strategies could be implemented. Since then, the focus of research has included the isolation and characterisation of toxins (primarily neurotoxins), examination of the efficacy of commercially available antivenoms and, more recently, the use of liquid chromatography/mass spectrometry (LCMS) to aid in the analysis of whole venoms. Given the vast quantity of research undertaken over the past 70 yr we have tried to provide a short insight into some of this excellent work and identify areas requiring further examination.

CysView: protein classification based on cysteine pairing patterns

CysView is a web-based application tool that identifies and classifies proteins according to their disulfide connectivity patterns. It accepts a dataset of annotated protein sequences in various formats and returns a graphical representation of cysteine pairing patterns. CysView displays cysteine patterns for those records in the data with disulfide annotations. It allows the viewing of records grouped by connectivity patterns. CysView's utility as an analysis tool was demonstrated by the rapid and correct classification of scorpion toxin entries from GenPept on the basis of their disulfide pairing patterns. It has proved useful for rapid detection of irrelevant and partial records, or those with incomplete annotations. CysView can be used to support distant homology between proteins. CysView is publicly available at http://research.i2r.a-star.edu.sg/CysView/.

Characterisation of the biochemical and biological variations from the venom of the death adder species (Acanthophis antarcticus, A. praelongus and A. pyrrhus)

We report on species variation in the venoms of the three species of death adder; the Common death adder (Acanthophis antarcticus), the Northern death adder (Acanthophis praelongus) and the Desert death adder (Acanthophis pyrrhus). The venoms were found to vary in their biochemical (chromatography) and biological (PLA(2) activity, anticoagulant activity and reactivity with commercial death adder antivenom) properties. Each species produced significant differences in the profile and distribution of PLA(2) activity, when whole venom was applied to a cation-exchange Mono-S column. PLA(2) enzymes were purified from each venom and termed acanthoxin B (from A. praelongus), acanthoxin C (from A. pyrrhus) and the previously characterised acanthoxin A (from A. antarcticus). Acanthoxin B and C showed lower enzymatic activities than acanthoxin A (4.0, 13.7 and 23.9 micromol of phospholipid hydrolyzed/min/mg protein, respectively). N-terminal sequencing revealed acanthoxin B to share highest homology with the numerous PLA(2) isozymes (Pa-12C, Pa-1G, Pa-12A) from the King brown snake (Pseudechis australis) and Acanthin I from the Common death adder. Similar to acanthoxin A, acanthoxin C showed highest homology with Acanthin I/II, and pseudexin A-chain from the Red-bellied black snake (Pseudechis porphyriacus). Whole venom from A. antarcticus, A. praelongus and A. pyrrhus each showed weak anticoagulant activity (being able to prolong coagulation of the plasma for 107, 220 and 195 s, respectively). By immunodiffusion, each venom produced precipitation bands against commercial death adder antivenom.

Charge reversal of ammodytoxin A, a phospholipase A2-toxin, does not abolish its neurotoxicity

The positive charge concentrated at the C-terminal region of ammodytoxin (Atx) A, which is involved in presynaptic toxicity, has been reversed. A six-site mutant of AtxA (K108N/K111N/K127T/K128E/E129T/K132E , where K108N=Lys(108)-->Asn etc. ) was prepared, in which five out of seven C-terminal basic amino acid residues were substituted with neutral or acidic ones. The mutant was approximately 30-fold less lethal, but still neurotoxic. Consistent with this, its binding affinity for the neuronal receptors decreased by only a factor of five. Additionally, a single-site mutant of AtxA was prepared, with substitution at only one position (K127T) out of six mutated in the six-site mutant. Its toxicity indicated that most, if not all, of the six mutated residues partially contribute to the decreased lethality of the multiple-site mutant.