Conformational Preferences of the CalliFMRFamides and their Free-Acid Analogues

A molecular dynamics study was undertaken to determine the conformational basis for the differing activities of the insect neuropeptide hormones calliFMRFamide 3 (SPSQDFMRF-NH2), calliFMRFamide 5 (APGQDFMRF-NH2) and their corresponding free-acid analogues (SPSQDFM- RF-OH and APGQDFMRF-OH) in two insect bioassays. A simulated annealing protocol was used to determine the range of conformers available to the linear peptides. Analysis of the conformers obtained indicated that all the peptides exhibited distinct secondary structure preferences. These, when correlated with their biological activities, enabled the formulation of putative conformation- activity relationships for the peptides.