On the three-dimensional structure of the Hydra head activator neuropeptide

The structure of the Hydra head activator (HHA) neuropeptide has been previously studied using NMR, CD, and Raman spectroscopy and determined to contain 62-67% anti-parallel beta-pleated sheet, and predicted to assume a beta-turn near the amino terminus. We have utilized spectroscopic data with the Double-Iterated Kalman Filter (DIFK) technique and CHARMm molecular mechanics to produce a molecular model of the HHA neuropeptide. Consistent with the secondary structure prediction, an anti-parallel beta-pleated sheet topology was evident from the serine amino acid to the carboxyl terminus. Additionally, a beta-turn occurred near the amino carboxyl terminus. Results indicate that fluctuations occurring at both termini may serve to stabilize the structure ultimately allowing the amino terminus access to its receptor protein.