Sequence of two gonadotropin releasing hormones from tunicate suggest an important role of conformation in receptor activation

The primary structure of two forms of gonadotropin releasing hormone (GnRH) from tunicate (Chelyosoma productum) have been determined based on mass spectrometric and chemical sequence analyses, The peptides, tunicate GnRH-I and -II, contain features unprecedented in vertebrate GnRH, Tunicate GnRH-I contains a putative salt bridge between Asp(5) and Lys(8). A GnRH analog containing a lactam bridge between Asp(5) and Lys(8) mas found to increase release of estradiol compared with that of the native tunicate GnRH-I and -II, Tunicate GnRH-II contains a cysteine residue and was isolated as a dimeric peptide, These motifs suggest that the conformation plays an important role in receptor activation. (C) 1997 Federation of European Biochemical Societies.