title: Conformational energy analysis of melanostatin.
abstract: Conformational energy calculations were carried out on the hypothalamic hormone melanostatin, a tripeptide with the primary structure H-L-Pro-L-Leu-Gly-NH2. The calculated lowest energy conformation was a type II beta bend, very similar to that reported in an X-ray crystal study. This conformation, however, was only one of 109 low-energy structures (less than or equal to 3 kcal/mol above the global minimum), indicating that the molecule in solution exists as an ensemble of conformations and is very flexible, in agreement with relaxation data from n.m.r. measurements. A statistical analysis yielded an average end-to-end distance of 6.8 A and a bend probability of 0.62, suggesting that, in nonpolar solvents, bend structures predominate within the statistical ensemble. The statistical analysis, however, also yielded a probability of only 0.11 for the occurrence of a 4 leads to 1 hydrogen bond. Hence, the calculations show that, although bend conformations predominate, bends would be difficult to observe in solution if the experiments were designed only to detect 4 leads to 1 hydrogen bonds.
mesh_terms: D000818:Animals; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D007031:Hypothalamus; D009075:MSH Release-Inhibiting Hormone; D011487:Protein Conformation; D013329:Structure-Activity Relationship; D014961:X-Ray Diffraction
chemical_list: D009075:MSH Release-Inhibiting Hormone