During pregnancy, placental protein-13 (galectin-13) is highly expressed in the placenta and fetal tissue, and less so in maternal serum that is related to pre-eclampsia. To understand galectin-13 function at the molecular level, we solved its crystal structure and discovered that its dimer is stabilized by two disulfide bridges between Cys136 and Cys138 and six hydrogen bonds involving Val135, Val137, and Gln139. Native PAGE and gel filtration demonstrate that this is not a crystallization artifact because dimers also form in solution. Our biochemical studies indicate that galectin-13 ligand binding specificity is different from that of other galectins in that it does not bind β-galactosides. This is partly explained by the presence of Arg53 rather than His53 at the bottom of the carbohydrate binding site in a position that is crucial for interactions with β-galactosides. Mutating Arg53 to histidine does not re-establish normal β-galactoside binding, but rather traps cryoprotectant glycerol molecules within the ligand binding site in crystals of the R53H mutant. Moreover, unlike most other galectins, we also found that GFP-tagged galectin-13 is localized within the nucleus of HeLa and 293 T cells. Overall, galectin-13 appears to be a new type of prototype galectin with distinct properties.

中文翻译：

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Galectin-13是另一种原型半乳凝素，它不结合β-半乳糖苷，而是通过Cys-136和Cys-138之间的分子间二硫键形成二聚体。

在怀孕期间，胎盘蛋白13（galectin-13）在胎盘和胎儿组织中高表达，而在与子痫前期有关的母体血清中则少表达。为了了解galectin-13在分子水平上的功能，我们解决了其晶体结构，并发现其二聚体被Cys136和Cys138之间的两个二硫键和涉及Val135，Val137和Gln139的六个氢键稳定。天然PAGE和凝胶过滤证明这不是结晶伪影，因为二聚体也会在溶液中形成。我们的生化研究表明，galectin-13配体的结合特异性不同于其他galectins，因为它不结合β-半乳糖苷。部分原因是碳水化合物结合位点底部的Arg53而不是His53的存在，该位置对于与β-半乳糖苷的相互作用至关重要。将Arg53突变为组氨酸并不能重新建立正常的β-半乳糖苷结合，而是将冷冻保护剂甘油分子捕获在R53H突变体晶体的配体结合位点内。此外，与大多数其他半乳糖凝集素不同，我们还发现带有GFP标签的半乳糖凝集素13位于HeLa和293 T细胞的核内。总体而言，半乳凝素13似乎是一种新型半乳凝素，具有独特的特性。与大多数其他半乳凝素不同，我们还发现带有GFP标签的半乳凝素13位于HeLa和293 T细胞的核内。总体而言，半乳凝素13似乎是一种新型半乳凝素，具有独特的特性。与大多数其他半乳凝素不同，我们还发现带有GFP标签的半乳凝素13位于HeLa和293 T细胞的核内。总体而言，半乳凝素13似乎是一种新型半乳凝素，具有独特的特性。