Presence of transient helical segments in the galanin-like peptide evident from (1)H NMR, circular dichroism, and prediction studies

Galanin and its newly discovered relative galanin-like peptide (GALP) are neuropeptides that are implicated in the neuroendocrine regulation of body weight and reproduction. GALP encompasses within its sequence the first 13 residues of galanin, known to be crucial to binding and activation of galanin receptor (GalR) subtypes. Using 2D-NMR and circular dichroism spectroscopy we demonstrated that GALP does not adopt a preferred conformation in pure water alone. However, it shows characteristics of transient turn-like structures in two distinct regions of its sequence, 11-23 and 41-49. These transient ordered structures, nascent helices, probably form stable helical structures upon addition of the helix-inducing solvent, trifluoroethanol, as determined by circular dichroism studies. Secondary structure prediction methods also predict the presence of two helical regions in the sequence of GALP overlapping reasonably with those regions identified as nascent helical structures by experimental methods.