Tertiary structure of H-Pro-Leu-Gly-NH2, the factor that inhibits release of melanocyte stimulating hormone, derived by conformational energy calculations.

Conformational energy calculations were carried out on H-Pro-Leu-Gly-NH(2), the factor that inhibits the release of melanocyte stimulating hormone, and its biologically active analog, H-Pro-Ala-Gly-NH(2). Both peptides were found to be relatively compact molecules that retain, however, some degree of flexibility. After structure refinement, H-Pro-Leu-Gly-NH(2) possesses at least three preferred compact conformations. Two of these conformations occupy rather broad and flat energy troughs, while a third occupies a narrow and deep potential energy well. This third structure, which consists of a 10-membered beta-turn closed by a (4 --> 1) hydrogen bond between the proton of the trans carboxamide of Gly and the C=O of Pro, is the one that was proposed for H-Pro-Leu-Gly-NH(2) in dimethylsulfoxide and was also found by x-ray analysis.