Nuclear Magnetic Resonance Solution Conformation of α-Conotoxin AuIB, an α3β4 Subtype-selective Neuronal Nicotinic Acetylcholine Receptor Antagonist

The neuronal nicotinic acetylcholine receptors constitute a highly diverse group, with subtypes consisting of pentameric combinations of alpha and beta subunits. alpha-Conotoxins are a homologous series of small peptides that antagonize these receptors. We present the three-dimensional solution structure of alpha-conotoxin AuIB, the first 15-residue alpha-conotoxin known to selectively block the alpha(3)beta(4) nicotinic acetylcholine receptor subtype. The pairwise backbone and heavy-atom root mean square deviation for an ensemble of 20 structures are 0.269 and 0.720 A, respectively. The overall fold of alpha-conotoxin AuIB closely resembles that of the alpha4/7 subfamily alpha-conotoxins. However, the absence of Tyr(15), normally present in other alpha4/7 members, results in tight bending of the backbone at the C terminus and effectively renders Asp(14) to assume the spatial location of Tyr(15) present in other neuronal alpha4/7 alpha-conotoxins. Structural comparison of alpha-conotoxin AuIB with the alpha(3)beta(2) subtype-specific alpha-conotoxin MII shows different electrostatic surface charge distributions, which may be important in differential receptor subtype recognition.