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.

免疫调节 Siglec 由其糖蛋白和糖脂配体控制。Siglec-糖脂相互作用通常在脂质双层的背景之外进行研究，而忽略了糖脂在膜中的复杂行为。通过优化脂质体配方来剖析 Siglec-糖脂相互作用，表明 Siglec-6 可以独立于其规范结合口袋识别糖脂，这表明 Siglec-6 拥有一个为识别双层中的糖脂而定制的二级结合口袋。一组合成新糖脂用于探测这种糖脂结合袋对 Siglec-6 的特异性，从而导致开发出一种新糖脂，与天然糖脂相比，它对 Siglec-6 具有更高的亲和力。这种新糖脂有助于将脂质体递送至人类肥大细胞上的 Siglec-6，记忆 B 细胞和胎盘合体滋养细胞。Siglec-6 对糖脂识别的生理相关性揭示了细胞外囊泡的结合和内化。这些结果证明了 Siglec-6 识别膜中糖脂的独特且生理相关的能力。