Rapid modification of proteins using a rapamycin-inducible tobacco etch virus protease system

Background: The ability to disrupt the function of a specific protein on a rapid time scale provides a powerful tool for biomedical research. Specific proteases provide a potential method to selectively cleave a chosen protein, but rapid control of protease activity is difficult. Methodology/Principal Findings: A heterologous expression system for rapid target-directed proteolysis in mammalian cells was developed. The system consists of an inducible NIa protease from the tobacco etch virus (TEVp) and a chosen protein into which a TEVp substrate recognition sequence (TRS) has been inserted. Inducible activity was conferred to the TEVp using rapamycin-controlled TEVp fragment complementation. TEVp activity was assayed using a FRET-based reporter construct. TEVp expression was well tolerated by mammalian cells and complete cleavage of the substrate was possible. Cleavage at 37uC proceeded exponentially with a time constant of approximately 150 minutes. Attempts to improve cleavage efficiency were hampered by substantial background activity, which was attributed to inherent affinity between the TEVp fragments. A second TEVp assay, based on changes in inactivation of a modified KV3.4 channel, showed that functional properties of a channel can be using altered using an inducible TEVp system. Similar levels of background activity and variability were observed in both electrophysiological and FRET assays. Conclusions/Significance: The results suggested that an optimum level of TEVp expression leading to sufficient inducibl