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

Abstract

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.

Chemoenzymatic synthesis of genetically-encoded multivalent liquid N-glycan arrays

“…Asialoglycans exhibited no statistically significant binding to SNA-I and CD22 proteins or CD22 + cells at any density. We previously confirmed that decrease of lectin–glycan interactions at high glycan density occurs due to steric occlusion 38 , 61 , here we tested this again by making a phage that displayed a mixture of sialylated and non-sialylated glycans (Supplementary Fig. 41 ).…”

Elusive Protein–Glycosphingolipid Interactions Revealed by Membrane Anchor-Assisted Native Mass Spectrometry

“…55 To explain the variation in binding profiles observed with the different methods, it was proposed that not only affinity but other factors are important for the detection of these interactions, such as steric crowding and the differing presentation of interactions in solution and in a lipid bilayer. 55 To more firmly establish the ganglioside binding properties of Siglec-1, MEAN-nMS was performed using a DBCO-labeled small monomeric Siglec-1 fragment, consisting of its first three extracellular domains, and the panel of ganglioside-containing NDs described above. Notably, signal corresponding to the 1:1 complex of the membrane anchor-linked Siglec-1 bound to each of the gangliosides was detected (Figures 2c,d, 3c, and S10), with F GSL ranging from 0.5 to 0.8.…”

“…Recently, the specificities of human Siglecs 1-11 and -15 for gangliosides were profiled using four different assays . Binding data for a soluble dimeric Siglec-1-Fc fusion complexed with tetrameric Strep-Tactin horseradish peroxidase conjugate measured with a lipid bilayer-free ELISA suggested that all nine gangliosides tested (GM1, GM2, GD1a, GD1b, GD3, GT1b, GM3, GM4 and GQ1b) are ligands, with GM2 and GM3 exhibiting the strongest avidities .…”

Bone-targeting exosome nanoparticles activate Keap1 / Nrf2 / GPX4 signaling pathway to induce ferroptosis in osteosarcoma cells

“…These EVs can be classified into three primary subtypes, namely microvesicles, EXOs, and apoptotic bodies. EVs are responsible for encapsulating cell-derived contents and mediating intercellular communication locally and over long distances transportation of functional substances, including RNA, DNA, proteins, and lipids [ 28 , 29 ]. These entities have the potential to serve as biomarkers, therapeutic agents, and drug delivery vehicles [ 30 ].…”