INSECT PROTHORACICOTROPIC HORMONE - A NEW MEMBER OF THE VERTEBRATE GROWTH-FACTOR SUPERFAMILY

Prothoracicotropic hormone (PTTH) is a brain neurosecretory protein th at controls insect development. PTTH of the silkmoth Bombyx mori is a homodimeric protein, the subunit of which consists of 109 amino acids. Clear-cut sequence similarity to any other proteins has not been obse rved. By disulfide-bond pattern analysis and modeling of the PTTH stru cture based on the known three-dimensional (3D) structures of growth f actor family with cystine-knot motif, we propose that the PTTH protome r adopts the fold unique to the structural superfamily of the growth f actors, beta-nerve growth factor (beta-NGF), transforming growth facto r-beta 2 (TGF-beta 2), and platelet-derived growth factor-BB (PDGF-BB) . The insect neurohormone PTTH appears to be a member of the growth fa ctor superfamily, sharing a common ancestral gene with the three verte brate growth factors, beta-NGF, TGF-beta 2 and PDGF-BB.