Development of a simple homogeneous assay to screen for inhibitors of N-acetylglucosamine-6-sulfotransferases

Abstract

L-selectin, a leukocyte adhesion molecule, plays a central role in lymphocyte homing to secondary lymphoid tissue and to certain sites of inflammation. Carbohydrate sulfation was implicated in this process, when it was demonstrated that carbohydrate sulfotransferase-mediated sulfation of N-acetylglucosamine (GlcNAc) within sialyl Lewis X of cognate endothelial ligands for L-selectin was an essential modification for L-selectin binding. The recently identified GlcNAc-6-sulfotransferases GlcNAc6ST-1 and -2, which facilitate GlcNAc sulfation by catalyzing the transfer of a sulfonyl group from 3 ′-phosphoadenosine 5 ′-phosphosulfate (PAPS) to the 6-hydroxy group of the acceptor GlcNAc moiety, contribute to the biosynthesis of the 6-sulfosialyl Lewis X motif. Due to their pivotal role in L-selectin ligand biosynthesis, this enzyme class has recently emerged as an important and relatively unexplored class of potential targets for anti-inflammatory therapy. However, no inhibitors have been reported to date and screening for lead inhibitors has been hampered by the lack of simple assay formats suitable for high-throughput screening. Here, we report the development of a simple homogeneous in vitro sulfotransferase assay using a newly synthesized biotinylated glycoside as a substrate. The assay is based on GlcNAc6ST-2-mediated [ 35S]sulfate transfer from [ 35S]PAPS to the biotinylated glycoside and subsequent detection using streptavidin-coated SPA beads. K m values with partially purified GlcNAc6ST-2 for PAPS and the biotinylated glycoside were estimated to be 8.4 and 34.5 μM, respectively. The sulfotransferase reaction could be inhibited by 3 ′,5 ′-ADP with an IC 50 of 2.1 μM. The assay can be operated in 384-well format; is characterized by a high signal-to-noise ratio, low variation, and excellent Z factors; and is highly suitable for high-throughput screening.