Toxicon 49 (2007) 1193–1199 A novel alpha conotoxin (a-PIB) isolated from C. purpurascens is selective for skeletal muscle nicotinic acetylcholine receptors Estuardo Lo´pez-Vera, Richard B. Jacobsen, Michael Ellison, Baldomero M. Olivera, Russell W. Teichert à Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, UT 84112, USA Received 25 September 2006; received in revised form 8 February 2007; accepted 9 February 2007 Available online 24 February 2007 Abstract The a-conotoxin family is comprised of peptides that share the following arrangement of cysteine residues in the primary amino acid sequence: –CC–C–C–, where each dash represents a variable number of amino acids. The number of amino acids between cysteine residues has been used to group the a-conotoxins into distinct subfamilies. These subfamilies include the a4/7-, a4/3- and a3/5-conotoxins, so named for the number of amino acids between 2nd/3rd and 3rd/4th cysteine residues, respectively. The a3/5-conotoxins antagonize vertebrate-muscle nicotinic acetylcholine receptors (nAChRs), while the a4/7- and a4/3-conotoxins primarily inhibit vertebrate neuronal nAChRs. To date, these three subfamilies are the most extensively characterized of the a-conotoxin family. Here we report the purification and characterization of an unusual a4/4-conotoxin, a-conotoxin PIB (a-PIB), from the venom of Conus purpurascens, with the following amino-acid sequence: ZSOGCCWNPACVKNRC (Z ¼ pyroglutamate, O ¼ hydroxyproline). This peptide demonstrates high affinity inhibition of vertebrate-muscle nAChRs, and paralytic effects when injected in vivo. Testing of a-PIB against other receptors indicated that the inhibitory effect is specific for skeletal muscle nAChRs. a-PIB shares the key biochemical and pharmacological characteristics of the a-conotoxin family. r 2007 Elsevier Ltd. All rights reserved. Keywords: a-conotoxins; nAChR; Conus snails 1. Introduction Peptides in the a-family of conotoxins were among the first components purified and characterized from Conus venoms approximately 30 years ago, including a-conotoxin GI (a-GI) (amino acid sequence: ECCN- PACGRHYSC) and a-conotoxin MI (a-MI) (amino acid sequence: GRCCHPACGKNYSC). These pep- tides were originally purified from fractions of crude venom that caused paralysis and death upon injection into fish or mice. Consistent with other venomous predators, it was not surprising that cone snails had evolved toxins among their venom components that had the ability to paralyze their fish prey. Similar to the first characterized paralytic toxin from snake venom, a-bungarotoxin, both a-GI and a-MI were identified as inhibitors of skeletal-muscle nicotinic acetylcholine receptors (nAChRs), which explained their paralytic effects (Gray et al., 1981; McIntosh et al., 1982). ARTICLE IN PRESS www.elsevier.com/locate/toxicon 0041-0101/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.toxicon.2007.02.007 à Corresponding author. Tel.: +1 801 581 8370; fax: +1 801 585 5010. E-mail address: teichert@biology.utah.edu (R.W. Teichert).