Solution structure of APETx1 from the sea anemone Anthopleura elegantissima: A new fold for an HERG toxin

Abstract

APETx1 is a 42-amino acid toxin purified from the venom of the sea anemone Anthopleura elegantissima. This cysteine-rich peptide possesses three disulfide bridges (C4-C37, C6-C30, and C20-C38). Its pharmacological target is the Ether-a-gogo potassium channel. We herein determine the solution structure of APETx1 by use of conventional two-dimensional 1H-NMR techniques followed by torsion angle dynamics and refinement protocols. The calculated structure of APETx1 belongs to the disulfide-rich all-beta structural family, in which a three-stranded anti-parallel beta-sheet is the only secondary structure. APETx1 is the first Ether-a-gogo effector discovered to fold in this way. We therefore compare the structure of APETx1 to those of the two other known effectors of the Ether-a-gogo potassium channel, CnErg1 and BeKm-1, and analyze the topological disposition of key functional residues proposed by analysis of the electrostatic anisotropy. The interacting surface is made of a patch of aromatic residues (Y5, Y32, and F33) together with two basic residues (K8 and K18) at the periphery of the surface. We pinpoint the absence of the central lysine present in the functional surface of the two other Ether-a-gogo effectors.

Developmental Biology of Neoplastic Growth

“…Their secondary structure is a triple-stranded antiparallel β-sheet, without α-helix (Fig. 2b) (Driscoll et al 1989a, b) also shared by Nav channel toxins isolated from sea anemones of the genera Anemonia and Anthopleura (Chagot et al 2005a;Torres and Kuchel 2004). BDS and APETx1 have an additional mini-antiparallel β-sheet at the N terminus and a long extracellular loop that connects the first and second strands of the antiparallel β-sheet (Chagot et al 2005a, Driscoll et al 1989a).…”

“…c Model representing the active surface of BgK, ShK and APETx1. Coloured amino acids represent key residues for the binding and function of BgK (Gilquin et al 2002;Racape et al 2002), ShK (Rauer et al 1999), and APETx1 (Chagot et al 2005a;Zhang et al 2007). Hydrophobic, basic and aliphatic residues are highlighted in green, blue, and yellow, respectively C2-C4, C3-C5 (Fig.…”

“…Kv3.4 current was almost completely inhibited (94%) by application of BDS-I (10 μM) and there was a slight effect on Kv3.1 (22 ± 10%, N = 5), and Kv3.2 (5 ± 4%, N = 4) currents family (erg1, erg2 and erg3). APETx1, owing to its different and unique structure, has been reported to be selective for the neuronal and cardiac (human and rat) ERG1 channels and does not compete with the two other scorpion toxins (Chagot et al 2005a;Restano-Cassulini et al 2006;Wanke and Restano-Cassulini 2007). A recent publication indicates that inhibition of human ERG3 currents is accomplished by modifying the voltage dependence of the channel gating ).…”

“…A potential interaction surface composed of three aromatic residues (Y5, Y32, and F33), two basic residues (K8 and K18), and three aliphatic amino acids (G7, G31 and L34) has been described for APETx1 (Chagot et al 2005a). In spite of a different fold, the APETx1 molecular surface shares some similarities (aromatic and basic residues) with the active surfaces of scorpion toxins (CnErg1 and BeKm1, Csαβ type of fold) which block erg channels.…”

“…The main difference is the absence of a central lysine (K) in APETx1. APETx1, like spider and scorpion toxins which modify K + channel gating, probably binds to the same region (S3C) in the outer vestibule of the channel (Chagot et al 2005a;Zhang et al 2007). …”