Isolation, synthesis and characterization of ω-TRTX-Cc1a, a novel tarantula venom peptide that selectively targets L-type Cav channels

Spider venoms are replete with peptidic ion channel modulators, often with novel subtype selectivity, making them a rich source of pharmacological tools and drug leads. In a search for subtype-selective blockers of voltage-gated calcium (Ca-v) channels, we isolated and characterized a novel 39-residue peptide, omega-TRTX-Cc1a (Cc1a), from the venom of the tarantula Citharischius crawshayi (now Pelinobius muticus). Cc1a is 67% identical to the spider toxin omega-TRTX-Hg1a, an inhibitor of Ca(v)2.3 channels. We assembled Cc1a using a combination of Boc solid-phase peptide synthesis and native chemical ligation. Oxidative folding yielded two stable, slowly interconverting isomers. Cc1a preferentially inhibited Ba2+ currents (I-Ba) mediated by L-type (Ca(v)1.2 and Ca(v)1.3) Ca-v channels heterologously expressed in Xenopus oocytes, with half-maximal inhibitory concentration (IC50) values of 825 nM and 2.24 mu M respectively. In rat dorsal root ganglion neurons, Cc1a inhibited I-Ba mediated by high voltage-activated Ca-v channels but did not affect low voltage-activated T-type Ca-v channels. Cc1a exhibited weak activity at Na(v)1.5 and Na(v)1.7 voltage-gated sodium (Na-v) channels stably expressed in mammalian HEK or CHO cells, respectively. Experiments with modified Cc1a peptides, truncated at the N-terminus (Delta G1-E5) or C-terminus (Delta W35-V39), demonstrated that the N- and C-termini are important for voltage-gated ion channel modulation. We conclude that Cc1a represents a novel pharmacological tool for probing the structure and function of L-type Cav channels. (C) 2014 Elsevier Inc. All rights reserved.