Institute of Biomedical Sciences.
Institute of Biological Chemistry.
Glycobiology. 2019 Dec 12;30(1):49-57. doi: 10.1093/glycob/cwz075.
Galectins are β-galactoside-binding animal lectins primarily found in the cytosol, while their carbohydrate ligands are mainly distributed in the extracellular space. Cytosolic galectins are anticipated to accumulate on damaged endocytic vesicles through binding to glycans initially displayed on the cell surface and subsequently located in the lumen of the vesicles, and this can be followed by cellular responses. To facilitate elucidation of the mechanism underlying this process, we adopted a model system involving induction of endocytic vesicle damage with light that targets the endocytosed amphiphilic photosensitizer disulfonated aluminum phthalocyanine. We demonstrate that the levels of galectins around damaged endosomes are dependent on the composition of carbohydrates recognized by the proteins. By super resolution imaging, galectin-3 and galectin-8 aggregates were found to be distributed in distinct microcompartments. Importantly, galectin accumulation is significantly affected when cell surface glycans are altered. Furthermore, accumulated galectins can direct autophagy adaptor proteins toward damaged endocytic vesicles, which are also significantly affected following alteration of cell surface glycans. We conclude that cytosolic galectins control cellular responses reflect dynamic modifications of cell surface glycans.
半乳糖凝集素是一种主要存在于细胞质中的β-半乳糖苷结合动物凝集素，而其碳水化合物配体主要分布在细胞外空间。细胞质半乳糖凝集素预计通过与最初在细胞表面显示、随后位于小泡腔中的糖结合，在受损的内吞小泡上积累，随后会引发细胞反应。为了阐明这一过程的机制，我们采用了一种模型系统，该系统涉及用光诱导内吞小泡损伤，用光靶向内吞的两亲性光敏剂二磺化铝酞菁。我们证明了受损内体周围半乳糖凝集素的水平取决于蛋白质识别的碳水化合物的组成。通过超分辨率成像，发现凝集素-3 和凝集素-8 聚集物分布在不同的微区室中。重要的是，当细胞表面糖发生改变时，凝集素的积累会受到显著影响。此外，积累的凝集素可以将自噬衔接蛋白引导到受损的内吞小泡上，而当细胞表面糖发生改变时，这些小泡也会受到显著影响。我们的结论是，细胞质半乳糖凝集素控制细胞反应，反映了细胞表面糖的动态修饰。
