![](/images/gifchars/omega.gif)
-Conotoxin MVIIA is a 25-residue, disulfide-bridged polypeptide from the venom of thesea snail
Conus magus that binds to neuronal N-type calcium channels. It forms a compact folded structure,presenting a loop between Cys8 and Cys15 that contains a set of residues critical for its binding. The loopdoes not have a unique defined structure, nor is it intrinsically flexible. Broadening of a subset of resonancesin the NMR spectrum at low temperature, anomalous temperature dependence of the chemical shifts ofsome resonances, and exchange contributions to
J(0) from
13C relaxation measurements reveal thatconformational exchange affects the residues in this loop. The effects of this exchange on the calculatedstructure of
![](/images/gifchars/omega.gif)
-conotoxin MVIIA are discussed. The exchange appears to be associated with a change inthe conformation of the disulfide bridge Cys8-Cys20. The implications for the use of the
![](/images/gifchars/omega.gif)
-conotoxinsas a scaffold for carrying other functions is discussed.