7quh | pdb_00007quh
Siglec-8 in complex with therapeutic Fab AK002.
Structural highlights
FunctionSIGL8_HUMAN Putative adhesion molecule that mediates sialic-acid dependent binding to cells. Preferentially binds to alpha-2,3-linked sialic acid. Also binds to alpha-2,6-linked sialic acid. The sialic acid recognition site may be masked by cis interactions with sialic acids on the same cell surface. Publication Abstract from PubMedHuman sialic acid binding immunoglobulin-like lectin-8 (Siglec-8) is an inhibitory receptor that triggers eosinophil apoptosis and can inhibit mast cell degranulation when engaged by specific monoclonal antibodies (mAbs) or sialylated ligands. Thus, Siglec-8 has emerged as a critical negative regulator of inflammatory responses in diverse diseases, such as allergic airway inflammation. Herein, we have deciphered the molecular recognition features of the interaction of Siglec-8 with the mAb lirentelimab (2C4, under clinical development) and with a sialoside mimetic with the potential to suppress mast cell degranulation. The three-dimensional structure of Siglec-8 and the fragment antigen binding (Fab) portion of the anti-Siglec-8 mAb 2C4, solved by X-ray crystallography, reveal that 2C4 binds close to the carbohydrate recognition domain (V-type Ig domain) on Siglec-8. We have also deduced the binding mode of a high-affinity analogue of its sialic acid ligand (9-N-napthylsufonimide-Neu5Ac, NSANeuAc) using a combination of NMR spectroscopy and X-ray crystallography. Our results show that the sialoside ring of NSANeuAc binds to the canonical sialyl binding pocket of the Siglec receptor family and that the high affinity arises from the accommodation of the NSA aromatic group in a nearby hydrophobic patch formed by the N-terminal tail and the unique G-G' loop. The results reveal the basis for the observed high affinity of this ligand and provide clues for the rational design of the next generation of Siglec-8 inhibitors. Additionally, the specific interactions between Siglec-8 and the N-linked glycans present on the high-affinity receptor FcepsilonRIalpha have also been explored by NMR. Structures of the Inhibitory Receptor Siglec-8 in Complex with a High-Affinity Sialoside Analogue and a Therapeutic Antibody.,Lenza MP, Atxabal U, Nycholat C, Oyenarte I, Franconetti A, Quintana JI, Delgado S, Nunez-Franco R, Garnica Marroquin CT, Coelho H, Unione L, Jimenez-Oses G, Marcelo F, Schubert M, Paulson JC, Jimenez-Barbero J, Ereno-Orbea J JACS Au. 2022 Dec 23;3(1):204-215. doi: 10.1021/jacsau.2c00592. eCollection 2023 , Jan 23. PMID:36711084[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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