SEQUENCE OF 2 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, tu nicate GnRH-I and -II, contain features unprecedented in vertebrate Gn RH, 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 L ys(8) mas found to increase release of estradiol compared with that of the native tunicate GnRH-I and -II, Tunicate GnRH-II contains a cyste ine residue and was isolated as a dimeric peptide, These motifs sugges t that the conformation plays an important role in receptor activation . (C) 1997 Federation of European Biochemical Societies.