Isolation, structure, and activity of GID, a novel α4/7-conotoxin with an extended N-terminal sequence

Using assay-directed fractionation of Conus geographus crude venom, we isolated α-conotoxin GID, which acts selectively at neuronal nicotinic acetylcholine receptors (nAChRs). Unlike other neuronally selective α-conotoxins, α-GID has a four amino acid N-terminal tail, γ-carboxyglutamate (Gla), and hydroxyproline (O) residues, and lacks an amidated C terminus. GID inhibits α7 and α3β2 nAChRs with IC50 values of 5 and 3 nM, respectively and is at least 1000-fold less potent at the α1β1γδ, α3β4, and α4β4 combinations. GID also potently inhibits the α4β2 subtype (IC50 of 150 nM). Deletion of the N-terminal sequence (GIDΔ1-4) significantly decreased activity at the α4β2 nAChR but hardly affected potency at α3β2 and α7 nAChRs, despite enhancing the off-rates at these receptors. In contrast, Arg12 contributed to α4β2 and α7 activity but not to α3β2 activity. The three-dimensional structure of GID is well defined over residues 4-19 with a similar motif to other α-conotoxins. However, despite its influence on activity, the tail appears to be disordered in solution. Comparison of GID with other α4/7-conotoxins which possess an NN(P/O) motif in loop II, revealed a correlation between increasing length of the aliphatic side-chain in position 10 (equivalent to 13 in GID) and greater α7 versus α3β2 selectivity.