title: Ligand-dependent responses of the silkworm prothoracicotropic hormone receptor, Torso, are maintained by unusual intermolecular disulfide bridges in the transmembrane region.
abstract: The insect membrane-protein, Torso, is a member of the receptor-tyrosine-kinase family, and is activated by its ligand, prothoracicotropic hormone (PTTH). Although PTTH is one of the most important regulators of insect development, the mechanism of Torso activation by the hormone has remained elusive. In this study, using heterologous expression in cultured Drosophila S2 cells, we detected ligand-independent dimerization of silkworm Torso, and found that the receptor molecules in the dimer were linked by intermolecular disulfide bridges. By examining the oligomerization states of several truncation and substitution mutants of Torso, atypical cysteine residues in the transmembrane region were identified as being responsible for the intermolecular linkage in the dimer. The replacement of all of the cysteines in the region with phenylalanines abolished the disulfide-bond-mediated dimerization; however, non-covalent dimerization of the mutant was detected using a cross-linking reagent, both with and without ligand stimulation. This non-covalent dimerization caused apparent receptor autophosphorylation independently of the ligand stimulation, but did not promote the ERK phosphorylation in the downstream signaling pathway. The unique Torso structure with the intermolecular disulfide bridges in the transmembrane region is necessary to maintain the ligand-dependent receptor functions of autophosphorylation and downstream activation.
authors.affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan.
authors.forename: Tadafumi
authors.initials: T
authors.lastname: Konogami
authors.affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan.
authors.forename: Yiwen
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan.
authors.forename: Mari H
authors.initials: MH
authors.lastname: Ogihara
authors.affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan.
authors.forename: Juri
authors.initials: J
authors.lastname: Hikiba
authors.affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kataoka
authors.affiliation: Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8562, Japan.
authors.forename: Kazuki
authors.initials: K
authors.lastname: Saito
mesh_terms: D000818:Animals; D012831:Bombyx; D002460:Cell Line; D003545:Cysteine / Q000737:chemistry; D019281:Dimerization; D004220:Disulfides / Q000737:chemistry*; D004330:Drosophila; D007301:Insect Hormones; D019476:Insect Proteins / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*
chemical_list: D004220:Disulfides; D007301:Insect Hormones; D019476:Insect Proteins; C009089:prothoracicotropic hormone; D020794:Receptor Protein-Tyrosine Kinases; D003545:Cysteine