BIOTINYLATED DERIVATIVES OF OMEGA-CONOTOXINS GVIA AND MVIID - PROBES FOR NEURONAL CALCIUM CHANNELS

The omega-conotoxins are small, disulfide-rich peptides which inhibit voltage-sensitive calcium channels. Biotinylated omega-conotoxins are potentially useful reagents for characterizing distinct subsets of cal cium channels. We describe the preparation and characterization of bio tinylated derivatives of two specific omega-conotoxins, GVIA and MVIID , which bind different calcium channel subtypes. Eight biotinylated de rivatives were tested; all specifically displaced binding of the radio labeled unbiotinylated omega-conotoxin. In general, the addition of on e biotin moiety decreased the apparent affinity for the receptor targe t site by only approximately 10-fold. However, derivatization of omega -conotoxin MVIID at the Lys10 residue caused a much more marked effect , a ca 500-fold decrease in affinity. These results indicate that the vicinity of the Lys10 residue of omega-conotoxin MVIID may be more cri tical for binding to the receptor target site than regions around othe r amino groups in omega-conotoxins GVIA and MVIID. Thus, high affinity biotinylated omega-conotoxin GVIA and MVIID derivatives have been che mically defined; the biotin groups have been shown to be accessible to streptavidin. Given the commercial availability of streptavidin coupl ed to various reporter groups, the biotinylated omega-conotoxin deriva tives described here should be widely useful for fluorescence, electro n microscopic or immunological applications.