Specificity of human galectins on cell surfaces

Area of Science:

• Glycobiology
• Molecular Cell Biology
• Protein-Carbohydrate Interactions

Background:

• Galectins are a family of β-galactoside-binding proteins with a conserved carbohydrate-recognition domain.
• Previous studies characterized galectin specificity primarily in artificial systems, revealing preferences for N-acetyllactosamine and substituted glycans.
• Understanding the specificity of cell-bound galectins interacting with natural cellular receptors was previously limited.

Purpose of the Study:

• To review and systematize data on the glycan specificity of different galectin types (proto-, chimera-, and tandem-repeat) when presented on the cell surface.
• To compare cell-surface galectin specificity with findings from artificial systems.
• To elucidate the factors governing galectin selectivity in a cellular context.

Main Methods:

• A novel model system was employed, involving the controlled incorporation of single galectins into the cell glycocalyx.
• Interaction of these modified cells with synthetic glycoprobes was measured using flow cytometry.
• Comparative analysis of data from cell-surface studies and artificial systems was performed.

Main Results:

• Cellular galectins show minimal binding to N-acetyllactosamine but bind to 3'-substituted oligolactosamines and oligomers.
• Tandem-repeat galectins recognize the disaccharide Lewis c (Le(c)) and retain high affinity for ABH blood group antigens.
• Galectins display increased selectivity for glycan interactions when integrated into the cell's glycocalyx.

Conclusions:

• Cell-surface galectins exhibit significantly different glycan binding preferences compared to galectins in solution.
• The cellular microenvironment, specifically endogenous glycans, plays a crucial role in determining galectin selectivity in vivo.
• Competitive interactions with endogenous cell glycans are the primary drivers of galectin specificity on the cell surface.