Probing the binding specificities of human Siglecs by cell-based glycan arrays

Area of Science:

• Glycobiology
• Immunology
• Cell Biology

Background:

• Siglecs are immune cell receptors that bind sialic acid sugars (sialoglycans).
• Understanding Siglec specificity for complex glycans and their cellular context is crucial but incomplete.
• The precise binding mechanisms of Siglecs to cell-surface glycoconjugates require further elucidation.

Purpose of the Study:

• To dissect Siglec interactions within the natural context of cell-surface glycoconjugates.
• To investigate the role of sialyltransferases and sulfotransferases in shaping the human sialome for Siglec recognition.
• To identify specific glycan epitopes and their associated Siglec binding preferences.

Main Methods:

• Generated a library of human HEK293 cells with combinatorial gene modifications (sialyltransferases, sulfotransferases).
• Displayed the human sialome on engineered cells to mimic natural glycoconjugate presentation.
• Analyzed Siglec binding preferences to distinct O-glycan structures and their protein contexts.

Main Results:

• Siglec-4, -7, and -15 showed distinct preferences for sialylated GalNAc-type O-glycans, influenced by O-glycan patterns on specific protein sequences.
• The sulfotransferase CHST1 was found to drive sialoglycan binding for Siglec-3, -8, -7, and -15.
• A novel binding epitope, 6'-sulfo-sialyl Lewis A (6'-Su-SLacNAc), was identified for Siglec-3 (CD33), a receptor implicated in Alzheimer's disease.

Conclusions:

• Cell-based display of the human sialome is a powerful platform for studying Siglec-glycan interactions.
• Siglec binding specificity is determined by complex glycan structures, protein context, and post-translational modifications like sulfation.
• The discovery of the 6'-Su-SLacNAc epitope for Siglec-3 offers new insights into Alzheimer's disease pathogenesis.