Ribonuclease A as a substrate of the protease from human immunodeficiency virus-1

Bovine pancreatic ribonuclease A (RNase) contains two bonds, Met29-Met30 and Tyr92-Pro93 which are representative of sites in the human immunodeficiency virus-1 (HIV-1) gag polyprotein precursors that are cleaved by the HIV-1 protease during viral maturation. Nevertheless, neither native nor performic acid-oxidized RNase is a substrate for the protease. However, RNase derivatives obtained by reduction and S-alkylation with iodoacetate or iodoacetamide undergo cleavage by the HIV-1 protease at a single site, Ala109-alkyl-Cys110, that is distinct from either of the two predicted bonds mentioned above. The neutral carboxyamido-methylcysteinyl derivative is cleaved 8 times faster than that containing the negatively charged carboxy-methyl substituent at P1'. Succinylation of these S-alkylated RNase derivatives creates a second site of cleavage by the protease between succinyl-Lys7 and Phe8. Thus, the pattern of cleavage of denatured RNase by the HIV-1 protease can be manipulated by chemical derivatization of the substrate, and the new sites of hydrolysis revealed by these studies add to our understanding of the specificity of this important enzyme.