Gangliosides, sialylated glycosphingolipids abundant in the nervous system, play crucial roles in neurotransmission, interaction with regulatory proteins, cell-cell recognition, and signaling. Altered gangliosides expression has been correlated with pathological processes, including cancer, inflammatory disorders, and autoimmune diseases. Gangliosides are important endogenous ligands of Siglecs (Sialic acid-binding immunoglobulin-type lectins), I-type lectins mostly expressed by immune cells, that specifically recognize sialylated glycans. Siglec-7, an inhibitory immune receptor on human natural killer cells, represents a potential target for tumor immunotherapy. Notably, the expression of Siglec-7 ligands is high in various cancers, such as pancreatic cancer and melanoma and lead to tumor immune evasion. Siglec-7 binds the disialylated ganglioside GD3, a tumor-associated antigen overexpressed on cancer cells to suppress immune responses. Using a combination of structural biology techniques, including Nuclear Magnetic Resonance (NMR), biophysical, and computational methods, the binding of Siglec-7 to GD3 and Gb3 derivatives is investigated, revealing the importance of ligand conformation in modulating binding energetics and affinity. The greater flexibility of Gb3 derivatives appears to negatively impact binding entropy, leading to lower affinity compared to GD3. A thorough understanding of these interactions could contribute to elucidating molecular mechanisms of cancer immune evasion and facilitate the development of ganglioside-based diagnostic and therapeutic strategies for cancer.

• Keywords
• NMR, gangliosides, siglec‐7, structural biology,
• MeSH
• Antigens, Differentiation, Myelomonocytic * metabolism   chemistry   MeSH
• Gangliosides * metabolism   chemistry   MeSH
• Lectins * metabolism   chemistry   MeSH
• Humans MeSH
• Ligands MeSH
• Magnetic Resonance Spectroscopy methods   MeSH
• Protein Binding MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Antigens, Differentiation, Myelomonocytic * MeSH
• Gangliosides * MeSH
• Lectins * MeSH
• Ligands MeSH
• SIGLEC7 protein, human MeSH Browser

Siglecs, sialic-acid-binding immunoglobulin-like lectins, are key immune cell receptors that recognize sialic acid residues on cell surfaces. Pathogens and tumor cells exploit Siglecs to evade immune responses and modulate immunity, contributing significantly to infectious disease and cancer pathogenesis. Siglec-7, primarily expressed on natural killer (NK) cells, functions as an inhibitory receptor, tightly regulating the immune activity. This study investigates the interaction between Siglec-7 and the capsular polysaccharide (CPS) of Neisseria meningitidis serogroup Y (Men-Y), a bacterium whose sialylated CPS is critical for virulence. We demonstrate that Men-Y CPS binds to inhibitory Siglec-7, potentially dampening immune recognition. We employed a multifaceted approach, combining biochemical and biophysical techniques to dissect this interaction. Enzyme-linked immunosorbent assays (ELISAs) and fluorescence titrations quantified the binding specificity and affinity. Ligand- and protein-based nuclear magnetic resonance (NMR) spectroscopy, coupled with computational modeling, provides detailed molecular insights. We highlight the critical influence of the Men-Y CPS conformation and sialic acid presentation on Siglec-7 binding. The specific arrangement of α-2,6-linked sialic acids on the CPS is crucial for Siglec-7 binding, demonstrating the importance of the CPS 3D structure. Preliminary immunological assays using stimulated U937 cells (a promonocytic cell line) further support the immunomodulatory role of Siglec-7 mediated by Men-Y CPS. These results offer valuable insights into the development of targeted therapeutic strategies against bacterial infections.

• Keywords
• Neisseria meningitidis serogroup Y CPS, Siglec-7, binding studies, immune evasion, sialic acid,
• Publication type
• Journal Article MeSH