Structure-function analysis of Lymantria testis ecdysiotropin: a search for the active core

A structure-function study was performed on the synthetic 21 residue neuropeptide, Lymantria testis ecdysiotropin (LTE), originally isolated from brains of Lymantria dispar pupae. The peptide induces ecdysteroid synthesis by testis sheaths of various lepidopteran species. LTE, as well as synthetic LTE 1-11, 11-21, and 11-15, stimulated synthesis in larval and pupal testes of Lymantria dispar at concentrations of 10(-9) to 10(-15) M; LTE 16-21 was weakly active, and an elongated LEU-LTE was inhibitory to synthesis at all but extremely low concentrations (10(-15) M). Since the sequence and polarity of residues in LTE 1-11, 11-15, and 11-21 are quite different, several parts of the molecule must activate receptors which initiate the cascade, resulting in ecdysiogenesis in Lepidopteran testes.