Effect of substrate residues on the P2 ' preference of retroviral proteinases

The substrate sequence requirements for preference toward P2 ' Glu residue by human immunodeficiency virus type 1 (HIV-l) proteinase were studied in b oth the matrix protein/ capsid protein (MA/CA) and CA/p2 cleavage site sequ ence contexts. These sequences represent typical type 1 (-aromatic*Pro-) an d type 2 (-hydrophobic* hydrophobic-) cleavage site sequences, respectively . While in the type 1 sequence context, the preference for P2 ' Glu over Il e or Gin was found to be strongly dependent on the ionic strength and the r esidues being outside the P2-P2 ' region of the substrate, it remained pref erable in the type 2 substrates when typical type 1 substrate sequence resi dues were substituted into the outside regions. The pH profile of the speci ficity constants suggested a lower pH optimum for substrates having P2 ' Gl u in contrast to those having uncharged residues, in both sequence contexts . The very low frequency of P2 ' Glu in naturally occurring retroviral clea vage sites of various retroviruses including equine infectious anemia virus (EIAV) and murine leukemia virus (MuLV) suggests that such a residue may n ot have a general regulatory role in the retroviral life cycle. In fact, un like HN-I and HIV-2, EIAV and MuLV proteinases do not favor P2 ' Glu in eit her the MA/CA or CA/p2 sequence contexts.