Design and Semisynthesis of Ubiquitin Extension Probes.

Activity-based ubiquitin probes serve as crucial tools for capturing and elucidating the molecular mechanisms of E3 ligase-catalyzed substrate ubiquitination. We recently reported a chemoenzymatic strategy for generating ubiquitin chain extension probes, which offers advantages such as mild reaction conditions, simple operation, and high specificity, thereby providing new opportunities for E3 enzyme research. This article details the experimental protocol for obtaining a K48-linked di-ubiquitin extension probe based on a substrate-Type II degron using the chemoenzymatic approach.