Isolation, Structure, and Activity of GID, a Novel [alpha]4/7-Conotoxin with an Extended N-terminal Sequence

• Published in: The Journal of biological chemistry Vol. 278; no. 5; pp. 3137 - 3144
• Main Authors: Nicke, A, Loughnan, M L, Millard, EL, Alewood, P F, Adams, D J, Daly, N L, Craik, D J, Lewis, R J
• Format: Journal Article
• Language: English
• Published: 31.01.2003
• Subjects: alpha -conotoxin; alpha -conotoxin GID; Conus geographus; Marine
• ISSN: 0021-9258; 1083-351X

Using assay-directed fractionation of Conus geographus crude venom, we isolated [alpha]-conotoxin GID, which acts selectively at neuronal nicotinic acetylcholine receptors (nAChRs). Unlike other neuronally selective [alpha]-conotoxins, [alpha]-GID has a four amino acid N-terminal tail, [gamma]-carboxyglutamate (Gla), and hydroxyproline (O) residues, and lacks an amidated C terminus. GID inhibits [alpha]7 and [alpha]3[beta]2 nAChRs with IC sub(50) values of 5 and 3 nM, respectively and is at least 1000-fold less potent at the [alpha]1[beta]1[gamma][delta], [alpha]3[beta]4, and [alpha]4[beta]4 combinations. GID also potently inhibits the [alpha]4[beta]2 subtype (IC sub(50) of 150 nM). Deletion of the N-terminal sequence (GID[Delta]1-4) significantly decreased activity at the [alpha]4[beta]2 nAChR but hardly affected potency at [alpha]3[beta]2 and [alpha]7 nAChRs, despite enhancing the off-rates at these receptors. In contrast, Arg super(12) contributed to [alpha]4[beta]2 and [alpha]7 activity but not to [alpha]3[beta]2 activity. The three-dimensional structure of GID is well defined over residues 4-19 with a similar motif to other [alpha]-conotoxins. However, despite its influence on activity, the tail appears to be disordered in solution. Comparison of GID with other [alpha]4/7-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 [alpha]7 versus [alpha]3[beta]2 selectivity.