Table_1_A brief history of galectin evolution.xlsx

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.

半乳聚糖是一类在脊椎动物中广泛存在且具有丰富多样性的碳水化合物结合蛋白家族，其在结构、配体结合特性以及生理功能方面均表现出极高的多样性和复杂性。与脊椎动物半乳聚糖存在明确关联的蛋白质已在原始两侧对称动物中发现。随着可访问且注释完善的两侧对称动物基因组数量的不断增加，我们得以通过同源分析揭示出关于该动物群体中半乳聚糖家族系统发育历史的全新假说。因此，我们可以追溯假定的原始两侧对称动物半乳聚糖的基因组定位，直至贻贝这一仍处于非常原始且缓慢演化的两侧对称动物谱系。令人感兴趣的是，我们的分析表明，最原始的脊索动物半乳聚糖很可能表现出类似于半乳聚糖-8的特征。这一基础存在的半乳聚糖以串联重复型为特征，具有两个碳水化合物识别结构域，以及N端结构域的神经氨酸酸结合特性，这是半乳聚糖-8的典型特征。借助同源分析，我们可以重建这一潜在原始半乳聚糖在现生有颌脊椎动物广泛半乳聚糖宇宙中的扩增过程。因此，我们能够区分由小规模复制产生的外显子同源和由全基因组复制产生的内含子同源。我们的发现支持了一个关于脊椎动物半乳聚糖家族各种成员起源的全新假设。这使我们得以揭示关于Gnatostomata中半乳聚糖亲缘关系的全新理论。此外，我们首次关注了圆口类动物中的半乳聚糖，作为有颌脊椎动物的同源群体，它们为我们提供了深入了解整个亚门进化历史的重要见解。我们的研究还突出了半乳聚糖家族中先前被忽视的一员——半乳聚糖相关蛋白2。这种蛋白似乎是在Gnathostomata中广泛分布的原始串联重复祖先的等位基因，由于它具有非经典半乳糖结合序列模式和在哺乳动物进化过程中丢失的事实，它并未成为半乳聚糖研究的焦点。