Trap for Sugar-Protein Partners

Carbohydrate-protein interactions occur in the immune system and throughout biology, but details about these contacts are poorly understood. Light-activated sugars have been used to trap some of these transient interactions via cross-linking, but bulky cross-linkers may influence binding. Now, Jennifer J. Kohler's team at the University of Texas Southwestern Medical Center and Stanford University has made a complementary photo-sugar with a less obtrusive cross-linker (J. Am. Chem. Soc., DOI: 10.1021/ja7109772). Kohler's team modified sialic acid, a sugar that mediates many interactions, with diazirine, a small cross-linker, at a position unlikely to hinder binding. They supplied white blood cells with photo-sialic acid or a precursor (shown) that the cells convert to photo-sialic acid. After inducing covalent bonding with ultraviolet light, the researchers detected a known sialic acid-dependent interaction that's thought to prevent accidental antibody production by white blood cells. Cross-linking worked even in cells containing naturally occurring sialic acid. Kohler now hopes to use photo-sugars to explore sialic acid's other roles.