title: m1-toxin isotoxins from the green mamba (Dendroaspis angusticeps) that selectively block m1 muscarinic receptors.
abstract: The venom of the green mamba, Dendroaspis angusticeps, was found to have at least six trace m1-specific toxins that block the binding of 3H-N-methylscopolamine to cloned m1 muscarinic receptors. Four were isolated by gel filtration, cation exchange HPLC and reversed-phase HPLC and named m1-toxins1-4. Recovery was 180, 90, 20 and 10 microg/g dry venom, respectively. m1-Toxin1 (the original m1-toxin) was found to have the sequence, L T C V K S N S I W F P T S E D C P D G Q N LC F K R W Q Y I S P R M Y D F T R G C A A T C P K A E Y R D V I N C C G T D K C N K, calculated mass = 7473 Da and calculated pI = 8.2. This sequence had been predicted previously from a cDNA cloned from the venom glands of this snake. The binding of m1-toxin1 was irreversible, so its Kd could not be determined. m1-Toxin2 differed only in proline-19, mass = 7455 and pI = 8.5. Partial sequence data for m1-toxin3 showed aspartate-7 and m1-toxin4 showed isoleucine-12, asparagine-16 and alanine-19. m1-Toxins1-4 have seven conserved amino acids not found in homologous mamba toxins that bind to other muscarinic receptors (MT1, MT2, m4-toxin = MT3, MT4, MT5, MTalpha and MTbeta). Some of these residues may be essential for m1-specificity. Since m1-toxin1 binds irreversibly in artificial cerebrospinal fluid at 37 degrees C, it is a particularly attractive antagonist for studies in vivo.
authors.affiliation: Department of Molecular and Cellular Pharmacology, University of Miami School of Medicine, FL 33101, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Carsi
authors.forename: L T
authors.initials: LT
authors.lastname: Potter
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002851:Chromatography, High Pressure Liquid; D006224:Cricetinae; D004546:Elapid Venoms / Q000737:chemistry / Q000633:toxicity*; D017815:Elapidae; D008969:Molecular Sequence Data; D018727:Muscarinic Antagonists / Q000633:toxicity*; D017510:Protein Folding; D043643:Receptor, Muscarinic M1; D011976:Receptors, Muscarinic / Q000187:drug effects*
chemical_list: D004546:Elapid Venoms; D018727:Muscarinic Antagonists; D043643:Receptor, Muscarinic M1; D011976:Receptors, Muscarinic