Vertebrate Ancient-Long Opsin Has Molecular Properties Intermediate between Those of Vertebrate and Invertebrate Visual Pigments
Vertebrate Ancient-Long Opsin Has Molecular Properties Intermediate between Those of Vertebrate and Invertebrate Visual Pigments
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DOI：
10.1021/bi201212z
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发表时间：
2011-12-06
期刊：
影响因子：
2.9
通讯作者：
Shichida, Yoshinori
中科院分区：
文献类型：
--
作者：
Sato, Keita;Yamashita, Takahiro;Shichida, Yoshinori
VA/瓦尔视蛋白是视蛋白系统发育树中与脊椎动物视色素密切相关的四种非视蛋白之一。以往的研究表明，在这些视蛋白中，副视蛋白和频视蛋白分别表现出与无脊椎动物视色素和脊椎动物视色素相似的分子特性。在这里，我们表明，VA/瓦尔视蛋白表现出的分子性质之间的parainopsin和pinopsin。来自热带爪蟾的瓦尔视蛋白在培养的细胞中表达，并且通过与11-顺式-视黄醛孵育重建在501 nm处具有最大吸收的色素。该颜料的光照射引起发色团的顺式至反式异构化，以形成在可见光区具有最大吸收的状态。这种状态具有激活Gi和Gt型G蛋白的能力。因此，瓦尔视蛋白的活性状态是可见光吸收中间体，其可能具有质子化的亚视黄基席夫碱作为其发色团，类似于对视蛋白的活性状态。然而，这种状态显然是光不敏感的，并且不显示对原始色素的逆反应，不像副视蛋白的活性状态，而是类似于视松蛋白。此外，瓦尔视蛋白的Gi激活效率介于视松蛋白和视副蛋白之间。因此，VA/瓦尔视蛋白的分子性质提供了从无脊椎动物到脊椎动物视色素的分子性质转换机制的见解。
VA/VAL opsin is one of the four kinds of nonvisual opsins that are closely related to vertebrate visual pigments in the phylogenetic tree of opsins. Previous studies indicated that among these opsins, parapinopsin and pinopsin exhibit molecular properties similar to those of invertebrate bistable visual pigments and vertebrate visual pigments, respectively. Here we show that VA/VAL opsin exhibits molecular properties intermediate between those of parapinopsin and pinopsin. VAL opsin from Xenopus tropicalis was expressed in cultured cells, and the pigment with an absorption maximum at 501 nm was reconstituted by incubation with 11-cis-retinal. Light irradiation of this pigment caused cis-to-trans isomerization of the chromophore to form a state having an absorption maximum in the visible region. This state has the ability to activate Gi and Gt types of G proteins. Therefore, the active state of VAL opsin is a visible light-absorbing intermediate, which probably has a protonated retinylidene Schiff base as its chromophore, like the active state of parapinopsin. However, this state was apparently photoinsensitive and did not show reverse reaction to the original pigment, unlike the active state of parapinopsin, and instead similar to that of pinopsin. Furthermore, the Gi activation efficiency of VAL opsin was between those of pinopsin and parapinopsin. Thus, the molecular properties of VA/VAL opsin give insights into the mechanism of conversion of the molecular properties from invertebrate to vertebrate visual pigments.