Muscarinic toxin‐like proteins from cobra venom

Abstract

Three new polypeptides were isolated from the venom of the Thailand cobra Naja kaouthia and their amino-acid sequences determined. They consist of 65-amino-acid residues and have four disulfide bridges. A comparison of the amino-acid sequences of the new polypeptides with those of snake toxins shows that two of them (MTLP-1 and MTLP-2) share a high degree of similarity (55-74% sequence identity) with muscarinic toxins from the mamba. The third polypeptide (MTLP-3) is similar to muscarinic toxins with respect to the position of cysteine residues and the size of the disulfide-confined loops, but shows less similarity to these toxins (30-34% sequence identity). It is almost identical with a neurotoxin-like protein from Bungarus multicinctus (TrEMBL accession number Q9W727), the sequence of which has been deduced from cloned cDNA only. The binding affinities of the isolated muscarinic toxin-like proteins towards the different muscarinic acetylcholine receptor (mAChR) subtypes (m1-m5) was determined in competition experiments with N-[3H]methylscopolamine using membrane preparations from CHO-K1 cells, which express these receptors. We found that MTLP-1 competed weakly with radioactive ligand for binding to all mAChR subtypes. The most pronounced effect was observed for the m3 subtype; here an IC50 value of about 3 microM was determined. MTLP-2 had no effect on ligand binding to any of the mAChR subtypes at concentrations up to 1 microM. MTLP-1 showed no inhibitory effect on alpha-cobratoxin binding to the nicotinic acetylcholine receptor from Torpedo californica at concentrations up to 20 microM.

Comparative venom gland transcriptomics ofNaja kaouthia(monocled cobra) from Malaysia and Thailand: elucidating geographical venom variation and insights into sequence novelty

“…MTLPs were reported to have low affinity towards muscle and neuronal-type receptors (nAChRs) (Kukhtina et al, 2000), while WTXs are weak antagonist to cholinergic receptors and non-lethal to mice by intravenous route, up to 10 mg/kg (Utkin et al, 2001a, 2001b). MTLP is the least expressed 3FTxs in the venom glands of both NK-M (two transcripts, 0.71%) and NK-T (one transcript, 0.47%) (Data S3; Table 5).…”

The first representative of glycosylated three‐fingered toxins

“…Materials N. kaouthia venom was obtained from cobras kept in captivity as described previously [19]. All the appropriate actions were taken to minimize discomfort to the snakes.…”

Muscarinic toxins: tools for the study of the pharmacological and functional properties of muscarinic receptors

“…2008). On the other hand, two three‐finger fold toxins with up to 50% sequence identity with MTs have been identified in the Naja kaouthia venom; however, despite this high degree of sequence identity, their apparent affinity for mAChRs is very low, reaching values up to μM range (Kukhtina et al. 2000).…”

“…Additionally, the recently identified Chinese cobra PLA 2 induces a weak contraction of the guinea pig ileum, suggesting a partial agonist effect on mAChRs (Huang et al 2008). On the other hand, two three-finger fold toxins with up to 50% sequence identity with MTs have been identified in the Naja kaouthia venom; however, despite this high degree of sequence identity, their apparent affinity for mAChRs is very low, reaching values up to lM range (Kukhtina et al 2000). Finally, one toxin isolated from Bungarus multicinctus venom, containing 82 residues and 10 cysteines, partially inhibits 3 H-QNB binding to M 2 receptor with low affinity.…”