Orthogonal-Group-Controlled Site-Selective I-Branching of Poly-N-acetyllactosamine Chains Reveals Unique Binding Specificities of Proteins towards I-Antigens.

Poly-N-acetyllactosamine (poly-LacNAc) is ubiquitously expressed on cell surface glycoconjugates, serving as the backbone of complex glycans and an extended scaffold that presents diverse glycan epitopes. The branching of poly-LacNAc, where internal galactose (Gal) residues have β1-6 linked N-acetylglucosamine (GlcNAc) attached, forms the blood group I-antigen, which is closely associated with various physiological and pathological processes including cancer progression. However, the underlying mechanisms remain unclear as many of the I-antigen sequences are undefined and inaccessible.