Siglec-6 mediates the uptake of extracellular vesicles through a noncanonical glycolipid binding pocket

Immunomodulatory Siglecs are controlled by their glycoprotein and glycolipid ligands. Siglec-glycolipid interactions are often studied outside the context of a lipid bilayer, missing the complex behaviors of glycolipids in a membrane. Through optimizing a liposomal formulation to dissect Siglec-glycolipid interactions, it is shown that Siglec-6 can recognize glycolipids independent of its canonical binding pocket, suggesting that Siglec-6 possesses a secondary binding pocket tailored for recognizing glycolipids in a bilayer. A panel of synthetic neoglycolipids is used to probe the specificity of this glycolipid binding pocket on Siglec-6, leading to the development of a neoglycolipid with higher avidity for Siglec-6 compared to natural glycolipids. This neoglycolipid facilitates the delivery of liposomes to Siglec-6 on human mast cells, memory B-cells and placental syncytiotrophoblasts. A physiological relevance for glycolipid recognition by Siglec-6 is revealed for the binding and internalization of extracellular vesicles. These results demonstrate a unique and physiologically relevant ability of Siglec-6 to recognize glycolipids in a membrane. Siglec-glycolipid interactions are often studied outside the context of a lipid bilayer. Here, the authors combine a variety of chemical biology techniques to demonstrate a unique and physiologically relevant ability of Siglec-6 to recognize glycolipids in a membrane.

Automated summary

By optimizing a liposomal formulation, it is shown that Siglec-6 can recognize glycolipids in a membrane through a secondary binding pocket. Synthetic neoglycolipids with higher avidity for Siglec-6 than natural glycolipids are developed, facilitating the delivery of liposomes to specific cells. The physiological relevance of glycolipid recognition by Siglec-6 is demonstrated for the binding and internalization of extracellular vesicles.