Purification and characterization of a unique, potent inhibitor of apamin binding from Leiurus quinquestriatus hebraeus venom

• Published in: The Journal of biological chemistry Vol. 263; no. 21; pp. 10192 - 10197
• Main Authors: Chicchi, G G, Gimenez-Gallego, G, Ber, E, Garcia, M L, Winquist, R, Cascieri, M A
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 25.07.1988; American Society for Biochemistry and Molecular Biology
• Subjects: Amino Acid Sequence; Amino Acids - analysis; Aminoacids, peptides. Hormones. Neuropeptides; Analytical, structural and metabolic biochemistry; Animals; apamin; Apamin - antagonists & inhibitors; Apamin - metabolism; Bee Venoms - antagonists & inhibitors; Biological and medical sciences; Cerebral Cortex - metabolism; Epinephrine - pharmacology; escorpion; Fundamental and applied biological sciences. Psychology; Guinea Pigs; In Vitro Techniques; Intracellular Membranes - metabolism; leiurotoxin I; Leiurus quinquestriatus hebraeus; Molecular Sequence Data; Muscle Contraction - drug effects; Muscle, Smooth - drug effects; Muscle, Smooth - physiology; nervous system; Potassium Channels; Proteins; Rats; Receptors, Neurotransmitter - drug effects; Receptors, Neurotransmitter - metabolism; scorpion; Scorpion Venoms - isolation & purification; Scorpion Venoms - pharmacology; scorpions; Sequence Homology, Nucleic Acid; sistema nervioso; Synaptosomes - metabolism; systeme nerveux; toxinas; toxine; toxins; veneno de serpientes; venin; venom; venoms; Brain; Purification; Calcium; Rat; Insecta; Rodentia; Molecular interaction; Ionic channel; Toxin; Vertebrata; Synaptosome; Mammalia; Fixation; Arthropoda; Venom; Leiurotoxin I; Apamine; Electrical conductance; Inhibitor; Invertebrata; Potassium
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(19)81496-5

An inhibitor of apamin binding has been purified to homogeneity in three chromatographic steps from the venom of the scorpion, Leiurus quinquestriatus hebraeus. The inhibitor, which we have named leiurotoxin I, represents less than 0.02% of the venom protein. It is a 3.4-kDa peptide with little structural homology to apamin although it has some homology to other scorpion toxins such as charybdotoxin, noxiustoxin, and neurotoxin P2. Leiurotoxin I completely inhibits 125I-apamin binding to rat brain synaptosomal membranes (Ki = 75 pM). Thus, it is 10-20-fold less potent than apamin. Leiurotoxin I is not a strictly competitive inhibitor of this binding reaction. Like apamin, leiurotoxin I blocks the epinephrine-induced relaxation of guinea pig teniae coli (ED50 = 6.5 nM), while having no effect on the rate or force of contraction in guinea pig atria or rabbit portal vein preparations. Thus, leiurotoxin I of scorpion venom and apamin of honeybee venom demonstrate similar activities in a variety of tissues, yet are structurally unrelated peptides. These two peptides should be useful in elucidating the role of the small conductance, Ca2+-activated K+ channels in different tissues.