Development of activity-based probes for cathepsin X

Cathepsin X is a lysosomal cysteine protease that functions as a Carboxypeptidase with broad substrate specificity. Cathepsin X was discovered only recently, and its physiological roles are still not well understood. A number of studies suggest that Cathepsin X may be involved in a variety of biological processes, including Cancer, aging and degenerative conditions of the brain, inflammation, and cellular communication. Here we present the synthesis and characterization of several activity-based probes (ABPs) that target active Cathepsin X. These ABPs were used to label Cathepsin X in complex lysates, whole cells, and in vivo. Furthermore, we have developed a method for selectively labeling and visualizing active Cathepsin X in vitro and in vivo. Overall, the probes developed in this study are valuable tools for the study of Cathepsin X function.