Ligand-dependent responses of the silkworm prothoracicotropic hormone receptor, Torso, are maintained by unusual intermolecular disulfide bridges in the transmembrane region.
Ligand-dependent responses of the silkworm prothoracicotropic hormone receptor, Torso, are maintained by unusual intermolecular disulfide bridges in the transmembrane region.
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DOI：
10.1038/srep22437
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发表时间：
2016-03-01
影响因子：
4.6
通讯作者：
Saito K
中科院分区：
文献类型：
--
作者：
Konogami T;Yang Y;Ogihara MH;Hikiba J;Kataoka H;Saito K
昆虫膜蛋白Torso是受体酪氨酸激酶家族的成员，并由其配体促前胸腺激素（PTTH）激活。虽然PTTH是昆虫发育的最重要的调节因子之一，但是该激素激活躯干的机制仍然是不清楚的。在这项研究中，利用异源表达在培养的果蝇S2细胞中，我们检测了家蚕躯干的配体非依赖性二聚体，并发现二聚体中的受体分子是通过分子间二硫键连接的。通过研究躯干的几个截断和取代突变体的寡聚化状态，跨膜区的非典型半胱氨酸残基被确定为负责二聚体中的分子间连接。用苯丙氨酸取代该区域中的所有半胱氨酸消除了二硫键介导的二聚化;然而，使用交联试剂检测到突变体的非共价二聚化，无论是否有配体刺激。这种非共价二聚化引起明显的受体自磷酸化，而不依赖于配体刺激，但不促进下游信号通路中的ERK磷酸化。在跨膜区具有分子间二硫桥的独特躯干结构对于维持配体依赖性受体的自磷酸化和下游活化功能是必需的。
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.