Glycobiology Unit, Institute of Reproductive Biology, Research Institute for Farm Animal Biology (FBN), Dummerstorf, Germany.
Front Immunol. 2023 Jun 29;14:1147356. doi: 10.3389/fimmu.2023.1147356. eCollection 2023.
Galectins are a family of carbohydrate-binding proteins found in vertebrates in great abundance and diversity in terms of both structure and ligand-binding properties as well as physiological function. Proteins with clear relationships to vertebrate galectins are already found in primitive Bilateria. The increasing amount of accessible well-annotated bilaterian genomes has allowed us to reveal, through synteny analyses, a new hypothesis about the phylogenetic history of the galectin family in this animal group. Thus, we can trace the genomic localization of the putative ancestral Bilateria galectin back to the scallops as a still very primitive slow-evolving bilaterian lineage. Intriguingly, our analyses show that the primordial galectin of the Deuterostomata most likely exhibited galectin-8-like characteristics. This basal standing galectin is characterized by a tandem-repeat type with two carbohydrate recognition domains as well as by a sialic acid binding property of the N-terminal domain, which is typical for galectin-8. With the help of synteny, the amplification of this potential primordial galectin to the broad galectin cosmos of modern jawed vertebrates can be reconstructed. Therefore, it is possible to distinguish between the paralogs resulting from small-scale duplication and the ohnologues generated by whole-genome duplication. Our findings support a substantially new hypothesis about the origin of the various members of the galectin family in vertebrates. This allows us to reveal new theories on the kinship relationships of the galectins of Gnatostomata. In addition, we focus for the first time on the galectines of the Cyclostomata, which as a sister group of jawed vertebrates providing important insights into the evolutionary history of the entire subphylum. Our studies also highlight a previously neglected member of the galectin family, galectin-related protein 2. This protein appears to be a widespread ohnologue of the original tandem-repeat ancestor within Gnathostomata that has not been the focus of galectin research due to its nonclassical galactose binding sequence motif and the fact that it was lost during mammalian evolution.
半乳糖凝集素是脊椎动物中丰富多样的一类糖结合蛋白，在结构、配体结合特性以及生理功能方面都具有多样性。在原始的两侧对称动物中已经发现了与脊椎动物半乳糖凝集素具有明显关系的蛋白质。越来越多的可访问的、注释良好的两侧对称动物基因组使我们能够通过基因同线性分析揭示出关于该动物类群半乳糖凝集素家族的进化历史的新假说。因此，我们可以将假定的原始两侧对称动物半乳糖凝集素的基因组定位追溯到扇贝，因为扇贝是一个仍然非常原始、进化缓慢的两侧对称动物谱系。有趣的是，我们的分析表明，后口动物的原始半乳糖凝集素很可能具有半乳糖凝集素 8 样的特征。这种基础的半乳糖凝集素的特征是具有串联重复类型的两个糖识别结构域，以及 N 端结构域的唾液酸结合特性，这是半乳糖凝集素 8 的典型特征。借助基因同线性，我们可以重建这种潜在原始半乳糖凝集素在现代有颌脊椎动物广泛的半乳糖凝集素宇宙中的扩增。因此，可以区分由小规模重复产生的同源基因和由全基因组重复产生的同线基因。我们的研究结果支持了关于脊椎动物半乳糖凝集素家族各个成员起源的全新假说。这使我们能够揭示关于栉水母门半乳糖凝集素亲缘关系的新理论。此外，我们首次关注了圆口纲的半乳糖凝集素，作为有颌脊椎动物的姐妹群，为整个亚门的进化历史提供了重要的见解。我们的研究还强调了半乳糖凝集素家族中一个以前被忽视的成员，半乳糖凝集素相关蛋白 2。这种蛋白质似乎是在颌口动物中原始串联重复祖先的广泛同线基因，由于其非经典的半乳糖结合序列基序以及在哺乳动物进化过程中丢失的事实，它一直不是半乳糖凝集素研究的重点。
