Adenovirus protease expressed in insect cells cleaves adenovirus proteins, ovalbumin and baculovirus protease in the absence of activating peptide

The adenovirus type 2 protease (EP) was expressed by infecting insect cells with a recombinant baculovirus. Immunoblot and activity analysis showed EP to be present in both the nucleus and cytoplasm. While the insect cell expressed EP was more soluble than the Escherichia coli expressed EP, its activity was one quarter of the latter, suggesting that eukaryotic postsynthetic modifications are not essential for enzyme activity. EP inactivated a cytoplasmic cathepsin-like baculovirus-encoded cysteine protease which carries a single EP cleavage site and which was capable of digesting most adenovirus structural proteins in vitro. In addition to cleavage of the baculovirus protease, the adenovirus EP was also able to cleave ovalbumin and canine adenovirus protein pre-VII, in the absence of activating peptide. EP activation therefore may occur by means of factors other than the specific activating peptide