Recombinant expression of a selective blocker of M(1) muscarinic receptors.

Mamba venoms contain peptides with high selectivity for muscarinic receptors. Due to the limited availability of the M(1) muscarinic receptor-selective MT7 or m1-toxin 1, the peptide was expressed in Sf9 cells using a synthetic cDNA and purified. The isolated peptide had over four orders of magnitude higher affinity for the M(1) compared to M(2)-M(5) muscarinic receptors. The peptide strongly inhibited Ca(2+) mobilisation through recombinant and endogenously expressed M(1) receptors, having no effect on the function of the other subtypes. The MT7 peptide provides a unique tool for identification and functional characterisation of M(1) receptors in cells and tissues.