Tagging Glycoproteins with Fluorescently Labeled GDP‐Fucoses by Using α1,3‐Fucosyltransferases

Fucose‐containing glycans mediate a variety of biological processes, but there is little information on reaction processes and mechanisms mediated by fucosyltransferases. We recently reported on fluorescently labeled GDP‐β‐L ‐fucose‐ATTO 550, which enabled monitoring of α1,3‐fucosyltransferase activity. Here we present an extension to the previously described results, based on the synthesis of a fluorescein‐isothiocyanate (FITC)‐labeled and two carboxyfluorescein‐labeled (FAM‐labeled) NDP‐β‐L ‐fucose derivatives, and applied all four compounds in labeling of different glycoproteins with the aid of four different fucosyltransferases. The labeling processes were analyzed by in‐gel fluorescence and fluorescence polarization measurements. Comparison with the ATTO‐labeled sugar revealed that the FITC‐labeled fucose was the best of these substrates, and that the bacterial enzyme HP‐FucT tolerated the fluorescent substrates better than human fucosyltransferases.