Abstract
Each of four basic residues of ω-conotoxin GVIA was replaced with alanine to study the role of basic residues for the binding of this toxin to N-type calcium channels. The activities of these analogs were estimated from the inhibitory action on 125I-ω-conotoxin GVIA binding to chick brain synaptic plasma membranes. The replacement of Arg 17, Lys 24 and Arg 25 resulted in no significant change in the activity and all of the analogs gave the same IC 50 value (0.15 nM) as that of native ω-conotoxin GVIA. The inhibitory action of [Ala 2]ω-conotoxin GVIA ( K2A) was 40-times less potent (IC 50 = 5.5 nM); however, full inhibition was achieved at a concentration above 0.1 μM. These results indicate that the Arg residue is not essential for the activity of ω-conotoxin GVIA. The nature of association to ion channels may be different between ω-conotoxin GVIA and μ-conotoxin GIIIA.
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