Traceless Protein-Selective Glycan Labeling and Chemical Modification

Executing
glycan editing at a molecular level not only is pivotal
for the elucidation of complicated mechanisms involved in glycan-relevant
biological processes but also provides a promising solution to potentiate
disease therapy. However, the precision control of glycan modification
or glyco-editing on a selected glycoprotein is by far a grand challenge.
Of note is to preserve the intact cellular glycan landscape, which
is preserved after editing events are completed. We report herein
a versatile, traceless glycan modification methodology for customizing
the glycoforms of targeted proteins (subtypes), by orchestrating chemical-
and photoregulation in a protein-selective glycoenzymatic system.
This method relies on a three-module, ligand-photocleavable linker-glycoenzyme
(L-P-G) conjugate. We demonstrated that RGD- or synthetic carbohydrate
ligand-containing conjugates (RPG and SPG) would not activate until
after the ligand-receptor interaction is accomplished (chemical regulation).
RPG and SPG can both release the glycoenzyme upon photoillumination
(photoregulation). The adjustable glycoenzyme activity, combined with
ligand recognition selectivity, minimizes unnecessary glycan editing
perturbation, and photolytic cleavage enables precise temporal control
of editing events. An altered target protein turnover and dimerization
were observed in our system, emphasizing the significance of preserving
the native physiological niche of a particular protein when precise
modification on the carbohydrate epitope occurs.