Despite their high sequence homology, the peptide neurotoxins omega-conotoxin 
MVIIA and MVIIC selectively block N- and P/Q-type calcium channels, 
respectively. To study the recognition mechanism of calcium channel subtypes, 
two chimeric analogs of omega-conotoxin MVIIA and MVIIC were synthesized by 
exchanging their N- and C-terminal halves. Binding assay for both N- and 
P/Q-type calcium channels showed that amino acid residues restricted to the 
N-terminal half are important for the recognition of N-type channels, whereas 
essential residues for P/Q-type channel recognition are widely spread over the 
whole omega-conotoxin molecule.