Table_2_Rhizostomins: A Novel Pigment Family From Rhizostome Jellyfish (Cnidaria, Scyphozoa).XLSX

Many pigments, such as melanins, are widely distributed throughout the animal kingdom. Others have arisen as novelties in particular lineages, for example, the Green Fluorescent Protein (GFP) found in cnidarians. While GFPs, widely used as fluorescent tags in biomedical research, are the most famous cnidarian example, other novel proteins have also been identified within this phylum. A blue protein that contains a Kringle (KR) domain inserted within a Frizzled cysteine-rich domain (Fz-CRD) was previously described from the jellyfish Rhizostoma pulmo (named rpulFKz1), however little is known about this pigment’s evolution or distribution among cnidarians. We performed a systematic search for homologs of this protein in published genomes and transcriptomes of 93 cnidarians. Phylogenetic analyses revealed eight predicted proteins that possess both domains in the same arrangement and that fall within the same clade as rpulFKz1. The sequence of one of these proteins contains motifs that match sequenced peptides of Cassio Blue, the blue pigment from Cassiopea xamachana. Another one of these proteins belongs to Stomolophus meleagris, and chemical studies on blue pigments that may occur in this genus have shown similarities to rpulFKz1 and Cassio Blue. Therefore, we hypothesize that the eight rpulFKz1 homologs identified are also pigment precursors. All precursors identified were exclusive to jellyfish in the order Rhizostomeae, so we herein name this new pigment family “rhizostomins.” Not all rhizostomes analyzed are blue, however, so these rhizostomin proteins may also be responsible for other colors, or perform other biochemical and biophysical roles. Previous studies have hypothesized that cnidarian pigments are photoprotective, and this study serves as basis for future investigations not only on the function of rhizostomins, but also on potential biotechnological applications for these proteins.

黑色素（melanins）等多种色素广泛分布于动物界。另有部分色素为特定类群所特有，例如刺胞动物（cnidarians）体内发现的绿色荧光蛋白（GFP）。尽管绿色荧光蛋白作为生物医学研究中广泛使用的荧光标记物，是最广为人知的刺胞动物来源蛋白，但该门类中还鉴定出了其他新型蛋白。此前曾从硝水母（Rhizostoma pulmo）中报道过一种蓝色蛋白，该蛋白包含插入于卷曲蛋白富含半胱氨酸结构域（Fz-CRD）内的Kringle（KR）结构域，并被命名为rpulFKz1；但目前对该色素的演化过程及其在刺胞动物中的分布情况仍知之甚少。我们针对93种刺胞动物已发表的基因组与转录组数据，开展了该蛋白同源序列的系统性搜索。系统发育分析显示，共有8个预测蛋白同时具备该结构域组合，且结构排布方式与rpulFKz1一致，并与rpulFKz1同属一个演化支。其中一种蛋白的序列中，含有与倒立水母（Cassiopea xamachana）来源的蓝色色素Cassio Blue的测序肽段相匹配的保守基序。另一种蛋白则来自沙海蜇（Stomolophus meleagris）；针对该属可能存在的蓝色色素开展的化学研究显示，其与rpulFKz1及Cassio Blue存在相似性。因此，我们推测本次鉴定得到的8个rpulFKz1同源蛋白同样属于色素前体。所有鉴定得到的前体蛋白均为根口水母目（Rhizostomeae）水母所特有，故我们将该新型色素家族命名为"rhizostomins"。不过并非所有被分析的根口水母类生物都呈现蓝色，因此这些rhizostomins蛋白可能还参与其他颜色的形成，或发挥其他生化与生物物理功能。此前有研究推测刺胞动物色素具有光保护作用，本研究不仅为后续探究rhizostomins的功能提供了基础，也为这些蛋白的潜在生物技术应用研究奠定了依据。