Sequential Autoprocessing of Marek’s Disease Herpesvirus Protease Differs from That of Other Herpesviruses

Herpesviruses encode a unique serine protease essential for viral capsid maturation. This protease undergoes autoprocessing at two sites, R and M, at the consensus sequence (V, L,I)P3-XP2-AP1/SP1' (where X is a polar amino acid). We observed complete autoprocessing at the R and M sites of Marek’s disease virus (MDV) protease following production of the polyprotein in Escherichia coli. Site-directed mutagenesis confirmed the predicted sequence of the R and M sites, with the M site sequence being nonconsensual: MP3-NP2-AP1/SP1'. Mutagenesis and expression kinetics studies suggested that the atypical MDV M site was cleaved exclusively by the processed short protease, a feature making MDV unique among herpesviruses