β-Trefoil lectins are galactose/N-acetyl galactosamine specific lectins, which are widely distributed across all kingdoms of life and are known to perform several important functions. However, there is no report available on the characterization of these lectins from protozoans. We have performed structural and biophysical studies on a β-trefoil lectin from Entamoeba histolytica (EntTref), which exists as a mixture of monomers and dimers in solution. Further, we have determined the affinities of EntTref for rhamnose, galactose and different galactose-linked sugars. We obtained the crystal structure of EntTref in a sugar-free form (EntTref_apo) and a rhamnose-bound form (EntTref_rham). A novel Cys residue-mediated dimerization was revealed in the crystal structure of EntTref_apo while the structure of EntTref_rham provided the structural basis for the recognition of rhamnose by a β-trefoil lectin for the first time. To the best of our knowledge, this is the only report of the structural, functional and biophysical characterization of a β-trefoil lectin from a protozoan source and the first report of Cys-mediated dimerization in this class of lectins.

中文翻译：

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来自溶组织内阿米巴的 β-三叶凝集素的单体和新型二硫键介导的二聚体形式的晶体结构。

β-三叶植物凝集素是半乳糖/ N-乙酰半乳糖胺特异性凝集素，广泛分布于生命的各个领域，并且已知具有多种重要功能。然而，没有关于这些来自原生动物的凝集素的表征的报告。我们对来自溶组织内阿米巴的 β-三叶凝集素进行了结构和生物物理研究(EntTref)，在溶液中以单体和二聚体的混合物形式存在。此外，我们已经确定了 EntTref 对鼠李糖、半乳糖和不同的半乳糖连接糖的亲和力。我们以无糖形式（EntTref_apo）和鼠李糖结合形式（EntTref_rham）获得了EntTref的晶体结构。在EntTref_apo的晶体结构中揭示了一种新的Cys残基介导的二聚化，而EntTref_rham的结构首次为β-三叶凝集素识别鼠李糖提供了结构基础。据我们所知，这是来自原生动物来源的 β-三叶凝集素的结构、功能和生物物理表征的唯一报告，也是此类凝集素中 Cys 介导的二聚化的第一份报告。