Galactans are linear polysaccharides of β(1→4)-linked galactose residues. Although they can antagonize galectin function, the nature of their binding to galectins needs to be better defined to develop them as drugs. Here, we investigated interactions between galectin-3 (Gal-3) and a series of galactans ranging in weight average molecular weight from 670 to 7550 Da. ¹⁵N-¹H HSQC NMR studies with ¹⁵N-labeled Gal-3 carbohydrate recognition domain (CRD) indicate that each of these galactans interacts primarily with residues in β-strands 4, 5 and 6 on the canonical, β-galactoside sugar binding S-face. Although these galactans also bind to full length Gal-3 (CRD plus N-terminal tail) to the same extent, it appears that binding to the S-face attenuates interactions between the CRD F-face and N-terminal tail, making interpretation of site-specific binding unclear. Following assignment of galactan ¹³C and ¹H resonances using HSQC, HMBC and TOCSY experiments, we used ¹³C-¹H HSQC data to demonstrate that the Gal-3 CRD binds to the terminal, non-reducing end of these galactans, regardless of their size, but with binding affinity increasing as the galactan chain length increases. Overall, our findings increase understanding as to how galactans interact with Gal-3 at the non-reducing, terminal end of galactose-containing polysaccharides as found on the cell surface.

中文翻译：

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Galectin-3选择性结合β（1→4）-半乳聚糖的末端非还原性末端，总亲和力随链长的增加而增加

半乳聚糖是β（1→4）连接的半乳​​糖残基的线性多糖。尽管它们可以拮抗半乳糖凝集素的功能，但需要更好地定义它们与半乳糖凝集素的结合性质，才能将其开发为药物。在这里，我们研究了galectin-3（Gal-3）与一系列半乳聚糖之间的相互作用，这些半乳聚糖的重均分子量范围为670至7550 Da。¹⁵ N- ¹ H HSQC NMR研究，其中¹⁵N标记的Gal-3碳水化合物识别结构域（CRD）表明，这些半乳聚糖中的每一个主要与规范的β-半乳糖苷糖结合S面上的β链4、5和6中的残基相互作用。尽管这些半乳聚糖也以相同程度结合全长Gal-3（CRD加N末端尾巴），但似乎与S面的结合减弱了CRD F面与N末端尾巴之间的相互作用，从而解释了特定于位点的结合尚不清楚。使用HSQC，HMBC和TOCSY实验分配半乳聚糖¹³ C和¹ H共振后，我们使用了¹³ C- ¹H HSQC数据证明Gal-3 CRD与这些半乳聚糖的末端非还原性末端结合，而不论其大小如何，但结合亲和力随半乳聚糖链长的增加而增加。总的来说，我们的发现增加了对半乳聚糖如何在细胞表面发现的含半乳糖的多糖的非还原性末端与Gal-3相互作用的认识。