Comparative studies on the substrate specificity of avian myeloblastosis virus proteinase and lentiviral proteinases.

The retroviral proteinase (PR) seems to play crucial roles in the viral life cycle, therefore it is an attractive target for chemotherapy. Previously we studied the specificity of human immunodeficiency virus (HIV) type 1 and type 2 as well as equine infectious anemia virus PRs using oligopeptide substrates. Here a similar approach is used to characterize the specificity of avian myeloblastosis virus (AMV) PR and to compare it with those of the previously characterized lentiviral PRs. All peptides representing naturally occurring Gag and Gag-Pol cleavage sites were substrates of the AMV PR. Only half of these peptides were substrates of HIV-1 PR. The Km values for AMV PR were in a micromolar range previously found for the lentiviral PRs; however, the kcat values were in a 10 30-fold lower range. A series of peptides containing single amino acid substitutions in a sequence representing a naturally occurring HIV cleavage site was used to characterize the seven substrate binding subsites of the AMV PR. The largest differences were found at the P4 and P2 positions of the substrate. Detailed analysis of the results by molecular modeling and comparison with previously reported data revealed the common characteristics of the specificity of the retroviral PRs as well as its strong dependence on the sequence context of the substrate.