Purification and characterization of acetylcholinesterase from desert cobra (Walterinnesia aegyptia) venom

Identification, Characterization and Synthesis of Walterospermin, a Sperm Motility Activator from the Egyptian Black Snake Walterinnesia aegyptia Venom

Animal venoms are small natural mixtures highly enriched in bioactive components. They are known to target at least two important pharmacological classes of cell surface receptors: ion channels and G protein coupled receptors. Since sperm cells express a wide variety of ion channels and membrane receptors, required for the control of cell motility and acrosome reaction, two functions that are defective in infertility issues, animal venoms should contain interesting compounds capable of modulating these two essential physiological functions. Herein, we screened for bioactive compounds from the venom of the Egyptian black snake Walterinnesia aegyptia (Wa) that possess the property to activate sperm motility in vitro from male mice OF1. Using RP-HPLC and cation exchange chromatography, we identified a new toxin of 6389.89 Da (termed walterospermin) that activates sperm motility. Walterospermin was de novo sequenced using a combination of matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF/TOF MS/MS) and liquid chromatography electrospray ionization quadrupole time-of-flight mass spectrometry (LC-ESI-QTOF MS/MS) following reduction, alkylation, and enzymatic proteolytic digestion with trypsin, chymotrypsin or V8 protease. The peptide is 57 amino acid residues long and contains three disulfide bridges and was found to be identical to the previously cloned Wa Kunitz-type protease inhibitor II (Wa Kln-II) sequence. Moreover, it has strong homology with several other hitherto cloned Elapidae and Viperidae snake toxins suggesting that it belongs to a family of compounds able to regulate sperm function. The synthetic peptide shows promising activation of sperm motility from a variety of species, including humans. Its fluorescently-labelled analog predominantly marks the flagellum, a localization in agreement with a receptor that controls motility function.

Neurobiology and therapeutic utility of neurotoxins targeting postsynaptic mechanisms of neuromuscular transmission

The neuromuscular junction (NMJ) is the principal site for the translation of motor neurochemical signals to muscle activity. Therefore, the release and sensing machinery of acetylcholine (ACh) along with muscle contraction are two of the main targets of natural toxins and pathogens, causing paralysis. Given pharmacology and medical advances, the active ingredients of toxins that target postsynaptic mechanisms have become of major interest, showing promise as drug leads. Herein, we review key facets of prevalent toxins modulating the mechanisms of ACh sensing and generation of the postsynaptic response, with muscle contraction. We consider the correlation between their outstanding selectivity and potency plus effects on motor function, and discuss emerging data advocating their usage for the development of therapies alleviating neuromuscular dysfunction.

Actiflagelin, a new sperm activator isolated from Walterinnesia aegyptia venom using phenotypic screening

Background

Sperm contains a wealth of cell surface receptors and ion channels that are required for most of its basic functions such as motility and acrosome reaction. Conversely, animal venoms are enriched in bioactive compounds that primarily target those ion channels and cell surface receptors. We hypothesized, therefore, that animal venoms should be rich enough in sperm-modulating compounds for a drug discovery program. Our objective was to demonstrate this fact by using a sperm-based phenotypic screening to identify positive modulators from the venom of Walterinnesia aegyptia.

Methods

Herein, as proof of concept that venoms contain interesting compounds for sperm physiology, we fractionated Walterinnesia aegyptia snake venom by RP-HPLC and screened for bioactive fractions capable of accelerating mouse sperm motility (primary screening). Next, we purified each compound from the positive fraction by cation exchange and identified the bioactive peptide by secondary screening. The peptide sequence was established by Edman sequencing of the reduced/alkylated compound combined to LC-ESI-QTOF MS/MS analyses of reduced/alkylated fragment peptides following trypsin or V8 protease digestion.

Results

Using this two-step purification protocol combined to cell phenotypic screening, we identified a new toxin of 7329.38 Da (actiflagelin) that activates sperm motility in vitro from OF1 male mice. Actiflagelin is 63 amino acids in length and contains five disulfide bridges along the proposed pattern of disulfide connectivity C₁-C₅, C₂-C₃, C₄-C₆, C₇-C₈ and C₉-C₁₀. Modeling of its structure suggests that it belongs to the family of three finger toxins with a noticeable homology with bucandin, a peptide from Bungarus candidus venom.

Conclusions

This report demonstrates the feasibility of identifying profertility compounds that may be of therapeutic potential for infertility cases where motility is an issue.

Fractionation and proteomic analysis of the Walterinnesia aegyptia snake venom using OFFGEL and MALDI-TOF-MS techniques

Animal venoms are complex mixtures of more than 100 different compounds, including peptides, proteins, and nonprotein compounds such as lipids, carbohydrates, and metal ions. In addition, the existing compounds show a wide range of molecular weights and concentrations within these venoms, making separation and purification procedures quite tedious. Here, we analyzed for the first time by MS the advantages of using the OFFGEL technique in the separation of the venom components of the Egyptian Elapidae Walterinnesia aegyptia snake compared to two classical methods of separation, SEC and RP-HPLC. We demonstrate that OFFGEL separates venom components over a larger scale of fractions, preserve respectable resolution with regard to the presence of a given compound in adjacent fractions and allows the identification of a greater number of ions by MS (102 over 134 total ions). We also conclude that applying several separating techniques (SEC and RP-HPLC in addition to OFFGEL) provides complementary results in terms of ion detection (21 more for SEC and 22 more with RP-HPLC). As a result, we provide a complete list of 134 ions present in the venom of W. aegyptia by using all these techniques combined.

Crystal structure of snake venom acetylcholinesterase in complex with inhibitory antibody fragment Fab410 bound at the peripheral site: evidence for open and closed states of a back door channel

The acetylcholinesterase found in the venom of Bungarus fasciatus (BfAChE) is produced as a soluble, non-amphiphilic monomer with a canonical catalytic domain but a distinct C terminus compared with the other vertebrate enzymes. Moreover, the peripheral anionic site of BfAChE, a surface site located at the active site gorge entrance, bears two substitutions altering sensitivity to cationic inhibitors. Antibody Elec410, generated against Electrophorus electricus acetylcholinesterase (EeAChE), inhibits EeAChE and BfAChE by binding to their peripheral sites. However, both complexes retain significant residual catalytic activity, suggesting incomplete gorge occlusion by bound antibody and/or high frequency back door opening. To explore a novel acetylcholinesterase species, ascertain the molecular bases of inhibition by Elec410, and document the determinants and mechanisms for back door opening, we solved a 2.7-Å resolution crystal structure of natural BfAChE in complex with antibody fragment Fab410. Crystalline BfAChE forms the canonical dimer found in all acetylcholinesterase structures. Equally represented open and closed states of a back door channel, associated with alternate positions of a tyrosine phenol ring at the active site base, coexist in each subunit. At the BfAChE molecular surface, Fab410 is seated on the long Ω-loop between two N-glycan chains and partially occludes the gorge entrance, a position that fully reflects the available mutagenesis and biochemical data. Experimentally based flexible molecular docking supports a similar Fab410 binding mode onto the EeAChE antigen. These data document the molecular and dynamic peculiarities of BfAChE with high frequency back door opening, and the mode of action of Elec410 as one of the largest peptidic inhibitors targeting the acetylcholinesterase peripheral site.

Walterinnesia aegyptia envenomation in a 22-year-old female: a case report

A 22-year-old woman was bitten on the third finger of her left hand by a Walterinnesia aegyptia (desert black cobra). Local signs included a marked swelling of the entire hand with pain along the left upper limb. Systemic reactions were irritability, fever, tachycardia, ventricular premature beats, nausea and high blood leukocytes count. About 15 h post-envenomation the patient had no symptoms except for a mild swelling of the hand. Despite the severe toxic venom composition of the W. aegyptia, the clinical course of our patient was relatively benign. This could be explained by the snake's behavior and the mechanism by which the venom penetrates the body. A survey of the literature revealed only a few clinical cases reported. Most of the information concerning W. aegyptia was collected from laboratory and animal studies.

Kinetics of human acetylcholinesterase inhibition by the novel experimental Alzheimer therapeutic agent, tolserine

Characterization of the kinetic parameters of tolserine, a novel acetylcholinesterase (AChE) inhibitor of potential in the therapy of Alzheimer's disease, to inhibit purified human erythrocyte AChE was undertaken for the first time. An IC(50) value was estimated by three methods. Its mean value was found to be 8.13 nM, whereas the IC(100) was observed to be 25.5 nM as calculated by single graphical method. The Michaelis-Menten constant (K(m)) for the hydrolysis of the substrate acetylthiocholine iodide was found to be 0.08 mM. Dixon as well as Lineweaver-Burk plots and their secondary replots indicated that the nature of the inhibition was of the partial non-competitive type. The value of K(i) was estimated as 4.69 nM by the primary and secondary replots of the Dixon as well as secondary replots of the Lineweaver-Burk plot. Four new kinetic constants were also investigated by polynomial regression analysis of the relationship between the apparent K(i) (K(Iapp)) and substrate concentration, which may open new avenues for the kinetic study of the inhibition of several enzymes by a wide variety of inhibitors in vitro. Tolserine proved to be a highly potent inhibitor of human AChE compared to its structural analogues physostigmine and phenserine.

Kinetics of the inhibition of acetylcholinesterase from desert cobra (Walterinnesia aegyptia) venom by local anesthetics: procaine and tetracaine

The kinetic parameters of W. aegyptia venom acetylcholinesterase (AChE) inhibition by procaine and tetracaine hydrochloride were investigated in the present study. Procaine and tetracaine reversibly inhibited the AChE activity in a concentration-dependent manner, the IC50 being about 0.28 and 0.04 mM, respectively. The Michaelis-Menten constant (K(m)) for the hydrolysis of acetylthiocholine iodide was found to be 0.051 mM with Vmax 10.2 mumole/min/mg protein. Both K(m) and Vmax were affected by procaine while only Vmax decreased with tetracaine. A Lineweaver-Burk plot and its secondary replot indicated that the nature of the inhibition is of the linear mixed type for procaine which is considered to be a mixture of competitive and noncompetitive types while the inhibition was noncompetitive for tetracaine. The values of Ki(slope) and K(intercept were estimated as 0.133 mM and 0.451 mM for procaine and 7.2 x 10(-3) mM for tetracaine, respectively, by the secondary replots of the Lineweaver-Burk plot.