Molecular and enzymatic characterization of the porcine endogenous retrovirus protease

The protease of the porcine endogenous retrovirus (PERV) subtypes A/B and C was recombinantly expressed in Escherichia coli as proteolytically active enzyme and characterized. The PERV Gag precursor was also recombinantly produced and used as the substrate in an in vitro enzyme assay in parallel with synthetic nonapeptide substrates designed according to cleavage site sequences identified in the PERV Gag precursor. The proteases of all PERV subtypes consist of 127 amino acid residues with an M(r) of 14,000 as revealed by determining the protease N and C termini. The PERV proteases have a high specificity for PERV substrates and do not cleave human immunodeficiency virus (HIV)-specific substrates, nor are they inhibited by specific HIV protease inhibitors. Among the known retroviral proteases, the PERV proteases resemble most closely the protease of the murine leukemia retrovirus.