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Characterization of a new muscarinic toxin from the venom of the Brazilian coral snake Micrurus lemniscatus in rat hippocampus

2011; Elsevier BV; Volume: 89; Issue: 25-26 Linguagem: Inglês

10.1016/j.lfs.2011.09.024

1879-0631

Daniel Coelho da Silva, Wyara Aparecida Araújo de Medeiros, Isabel de Fátima Correia Batista, Daniel C. Pimenta, Ivo Lebrun, Fernando Maurício Francis Abdalla, Maria Regina Lopes Sandoval,

Nicotinic Acetylcholine Receptors Study

We have isolated a new muscarinic protein (MT-Mlα) from the venom of the Brazilian coral snake Micrurus lemniscatus.This small protein, which had a molecular mass of 7,048Da, shared high sequence homology with three-finger proteins that act on cholinergic receptors. The first 12 amino acid residues of the N-terminal sequence were determined to be: Leu-Ile-Cys-Phe-Ile-Cys-Phe-Ser-Pro-Thr-Ala-His.The MT-Mlα was able to displace the [(3)H]QNB binding in the hippocampus of rats. The binding curve in competition experiments with MT-Mlα was indicative of two types of [(3)H]QNB-binding site with pK(i) values of 9.08±0.67 and 6.17±0.19, n=4, suggesting that various muscarinic acetylcholine receptor (mAChR) subtypes may be the target proteins of MT-Mlα. The MT-Mlα and the M(1) antagonist pirenzepine caused a dose-dependent block on total [(3)H]inositol phosphate accumulation induced by carbachol. The IC(50) values for MT-Mlα and pirenzepine were, respectively, 33.1 and 2.26 nM. Taken together, these studies indicate that the MT-Mlα has antagonist effect on mAChRs in rat hippocampus.The results of the present study show, for the first time, that mAChRs function is drastically affected by MT-Mlα since it not only has affinity for mAChRs but also has the ability to inhibit mAChRs.