phaffii for expressing α-cobratoxin

Three-finger toxins (3FTxs) have traditionally been obtained via venom fractionation of whole venoms from snakes. This method often yields functional toxins, but it can be difficult to obtain pure isoforms, as it is challenging to separate the many different toxins with similar physicochemical properties that generally exist in many venoms. This issue can be circumvented via the use of recombinant expression. However, achieving the correct disulfide bond formation in recombinant toxins is challenging and requires extensive optimization of expression and purification methods to enhance stability and functionality. In this study, we investigated the expression of α-cobratoxin, a well-characterized 3FTx from the monocled cobra (Naja kaouthia), in three different expression systems, namely Escherichia coli BL21 (DE3) cells with the csCyDisCo plasmid, Escherichia coli SHuffle cells, and Komagataella phaffii (formerly known as Pichia pastoris). While none of the tested systems yielded α-cobratoxin identical to the variant isolated from whole venom, the His6-tagged α-cobratoxin expressed in K. phaffii exhibited a comparable secondary structure according to circular dichroism spectra and similar binding properties to the α7 subunit of the nicotinic acetylcholine receptor. The findings presented here illustrate the advantages and limitations of the different expression systems and can help guide researchers who wish to express 3FTxs.

Cobratoxin Alleviates Cancer-Induced Bone Pain in Rats via Inhibiting CaMKII Signaling Pathway after Acting on M4 Muscarinic Cholinergic Receptors

Cancer-induced bone pain (CIBP) is a common pain in clinics, which can reduce the quality of life and increase the mortality of patients, but the treatment of CIBP is limited. This study was designed to investigate the analgesic effect of α-cobratoxin on CIBP and further to explore the molecular target and potential signal pathway. As shown by the mechanical allodynia test in a CIBP rat model, administration of α-cobratoxin produced significant analgesia in a dose-dependent manner, and the analgesic effects were blocked by pretreatment with an intrathecal injection of M4 mAChR-siRNA or intraperitoneal injection of tropicamide, an antagonist of M4 muscarinic cholinergic receptor. Whole-cell patch-clamp recording showed that α-cobratoxin can decrease the spontaneous firing and spontaneous excitatory postsynaptic currents of SDH neurons in CIBP rats. In primary lumber SDH neurons, intracellular calcium measurement revealed that α-cobratoxin decreased intracellular calcium concentration, and immunofluorescence demonstrated that M4 muscarinic cholinergic receptor and CaMKII/CREB were co-expressed. In the CIBP model and primary SDH neurons, Western blot showed that the levels of p-CaMKII and p-CREB were increased by α-cobratoxin and the effect of α-cobratoxin was antagonized by M4 mAChR-siRNA. The quantitative polymerase chain reaction (qPCR) results showed that α-cobratoxin downregulated the expression of proinflammatory cytokines through M4 muscarinic cholinergic receptor in SDH. These results suggest that α-cobratoxin may activate M4 muscarinic cholinergic receptor, triggering the inhibition of SDH neuronal excitability via CaMKII signaling pathway, thereby resulting in antagonistic effects in the CIBP rat model.

Snake Toxins Labeled by Green Fluorescent Protein or Its Synthetic Chromophore are New Probes for Nicotinic acetylcholine Receptors

Fluorescence can be exploited to monitor intermolecular interactions in real time and at a resolution up to a single molecule. It is a method of choice to study ligand-receptor interactions. However, at least one of the interacting molecules should possess good fluorescence characteristics, which can be achieved by the introduction of a fluorescent label. Gene constructs with green fluorescent protein (GFP) are widely used to follow the expression of the respective fusion proteins and monitor their function. Recently, a small synthetic analogue of GFP chromophore (p-HOBDI-BF₂) was successfully used for tagging DNA molecules, so we decided to test its applicability as a potential fluorescent label for proteins and peptides. This was done on α-cobratoxin (α-CbTx), a three-finger protein used as a molecular marker of muscle-type, neuronal α7 and α9/α10 nicotinic acetylcholine receptors (nAChRs), as well as on azemiopsin, a linear peptide neurotoxin selectively inhibiting muscle-type nAChRs. An activated N-hydroxysuccinimide ester of p-HOBDI-BF₂ was prepared and utilized for toxin labeling. For comparison we used a recombinant α-CbTx fused with a full-length GFP prepared by expression of a chimeric gene. The structure of modified toxins was confirmed by mass spectrometry and their activity was characterized by competition with iodinated α-bungarotoxin in radioligand assay with respective receptor preparations, as well as by thermophoresis. With the tested protein and peptide neurotoxins, introduction of the synthetic GFP chromophore induced considerably lower decrease in their affinity for the receptors as compared with full-length GFP attachment. The obtained fluorescent derivatives were used for nAChR visualization in tissue slices and cell cultures.

α-Conotoxins and α-Cobratoxin Promote, while Lipoxygenase and Cyclooxygenase Inhibitors Suppress the Proliferation of Glioma C6 Cells

Among the brain tumors, glioma is the most common. In general, different biochemical mechanisms, involving nicotinic acetylcholine receptors (nAChRs) and the arachidonic acid cascade are involved in oncogenesis. Although the engagement of the latter in survival and proliferation of rat C6 glioma has been shown, there are practically no data about the presence and the role of nAChRs in C6 cells. In this work we studied the effects of nAChR antagonists, marine snail α-conotoxins and snake α-cobratoxin, on the survival and proliferation of C6 glioma cells. The effects of the lipoxygenase and cyclooxygenase inhibitors either alone or together with α-conotoxins and α-cobratoxin were studied in parallel. It was found that α-conotoxins and α-cobratoxin promoted the proliferation of C6 glioma cells, while nicotine had practically no effect at concentrations below 1 µL/mL. Nordihydroguaiaretic acid, a nonspecific lipoxygenase inhibitor, and baicalein, a 12-lipoxygenase inhibitor, exerted antiproliferative and cytotoxic effects on C6 cells. nAChR inhibitors weaken this effect after 24 h cultivation but produced no effects at longer times. Quantitative real-time polymerase chain reaction showed that mRNA for α4, α7, β2 and β4 subunits of nAChR were expressed in C6 glioma cells. This is the first indication for involvement of nAChRs in mechanisms of glioma cell proliferation.