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Structure and Function of G-protein--Signal Coupling Protein

G蛋白--信号偶联蛋白的结构与功能

基本信息

批准号：
62480467
负责人：
TSUDA Motoyuki
金额：
$ 4.16万
依托单位：
Sapporo Medical College
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1987
资助国家：
日本
起止时间：
1987 至 1988
项目状态：
已结题

项目摘要

Photon absorption by rhodopsin triggers a transduction cascade, leading to an electrical signal in the photoreceptor of retina. Phototransduction of vertebrate photoreceptors are now established that G-protein (Gt: transducin) couples the photoexcited rhodopsin to cGMP hydrolysis and cGMP controls the cation permeability in the plasma membranes. Much less in known about either signal coupling proteins or the control of cation permeability in invertebrate photoreceptors. We found Gtpase (G-protein) in octopus photoreceptor membranes was activated by light just like vertebrate photoreceptors. In present work, the G-proteins were characterized by pertussis toxin and cholera toxin catalyzed ADP ribosylation. Gip alpha, the alpha-subunit of Gip of octopus rhodopsin, is ADP ribosylated by pertussis toxin, but not by cholera toxin, in the same way as Gi in the hormon system. The molecular weight of Gip alpha is 41 kDa like gip which is about 2 kDa more than Gt alpha. However the effect of light and nucleotides on the labeling of Gip alpha is just like gt alpha of vertebrate photoreceptors; Gip alpha of octopus ADP ribosylated most in the presence of GDP beta S in the dark. Light inhibits labeling. Both GTP hamma S and GppnHp were inhibitory even in the dark. Transducin (Gt) is labeled by both pertussis toxin and cholera toxin. In octopus microvilli, cholera toxin substrate is 46 kDa protein (Gsp alpha), but not Gip alpha(41 kDa). The extent of ratiolabeling of the 46 kDa protein depend on nucleotide present, GppNHp and GTP gamma S, greatly enhanced albeling, but GDP beta S and GTP are inhibitory. Labeling of GSP was not influenced by light, which suggests GSP might not be involved in phototransduction.

由视紫红质吸收的光子触发转导级联，导致视网膜光感受器中的电信号。脊椎动物光感受器的光转导现在被确定为G蛋白（Gt：transformin）将光激发的视紫红质耦合到cGMP水解，并且cGMP控制质膜中的阳离子渗透性。对无脊椎动物光感受器中的信号耦合蛋白或阳离子渗透性的控制知之甚少。我们发现章鱼感光细胞膜中的G蛋白Gtpase与脊椎动物的感光细胞一样，在光的作用下被激活。在本工作中，G-蛋白的特征在于百日咳毒素和霍乱毒素催化ADP核糖基化。Gip α是章鱼视紫红质的Gip的α亚基，与激素系统中的Gi相同，被百日咳毒素而不是霍乱毒素ADP核糖基化。Gip α的分子量为41 kDa，与gip相似，比Gt α大约2 kDa。然而，光和核苷酸对Gip α标记的影响就像脊椎动物光感受器的gt α一样;章鱼ADP的Gip α在黑暗中在GDP β S存在下最核糖化。光抑制标记。即使在黑暗中，GTP hamma S和GppnHp都是抑制性的。转导蛋白（Transducin，Gt）被百日咳毒素和霍乱毒素标记。在章鱼微绒毛中，霍乱毒素底物是46 kDa蛋白（Gsp α），而不是Gip α（41 kDa）。46 kDa蛋白的比例标记程度取决于核苷酸的存在，GppNHp和GTP γ S极大地增强了标记，但GDP β S和GTP是抑制性的。GSP的标记不受光的影响，这表明GSP可能不参与光转导。