Solution Conformation of αA-conotoxin EIVA, a Potent Neuromuscular Nicotinic Acetylcholine Receptor Antagonist from Conus ermineus

Abstract

We report the solution three-dimensional structure of an αA-conotoxin EIVA determined by nuclear magnetic resonance spectroscopy and restrained molecular dynamics. The αA-conotoxin EIVA consists of 30 amino acids representing the largest peptide among the α/αA-family conotoxins discovered so far and targets the neuromuscular nicotinic acetylcholine receptor with high affinity. αA-Conotoxin EIVA consists of three distinct structural domains. The first domain is mainly composed of the Cys3-Cys11-disulfide loop and is structurally ill-defined with a large backbone root mean square deviation of 1.91 Å. The second domain formed by residues His12-Hyp21 is extremely well defined with a backbone root mean square deviation of 0.52 Å, thus forming a sturdy stem for the entire molecule. The third C-terminal domain formed by residues Hyp22-Gly29 shows an intermediate structural order having a backbone root mean square deviation of 1.04 Å. A structurally ill-defined N-terminal first loop domain connected to a rigid central molecular stem seems to be the general structural feature of the αA-conotoxin subfamily. A detailed structural comparison between αA-conotoxin EIVA and αA-conotoxin PIVA suggests that the higher receptor affinity of αA-conotoxin EIVA than αA-conotoxin PIVA might originate from different steric disposition and charge distribution in the second loop "handle" motif.