Catalytic efficiency and vitality of HIV-1 proteases from African viral subtypes

The vast majority of HIV-1 infections in Africa are caused by the A and C v iral subtypes rather than the B subtype prevalent in the United States and Western Europe. Genomic differences between subtypes give rise to sequence variations in the encoded proteins, including the HIV-1 protease, Because s ome amino acid polymorphisms occur at sites that have been associated with drug resistance:in the B subtype, it is important to assess the effectivene ss of protease inhibitors that have been developed against different subtyp es. Here we report the enzymatic characterization of HIV-1 proteases with s equences found in drug-naive Ugandan adults. The A protease used in these s tudies differs in seven positions (I13V/E35D/M361/R41K/R57K/H69K/L89M) in r elation to the consensus B subtype protease. Another protease containing a subset of these amino acid polymorphisms (M361/R41K/H69K/L89M), which are f ound in subtype C and other HIV subtypes, also was studied. Both proteases were found to have similar catalytic constants, k(cat), as the B subtype. T he C subtype protease displayed lower K, values against two different subst rates resulting in a higher (2.4-fold) catalytic efficiency than the B subt ype protease, Indinavir, ritonavir, saquinavir, and nelfinavir inhibit the A and C subtype proteases with 2.5-7-fold and 2-4.5-fold weaker K(i)s than the B subtype. When all factors are taken into consideration it is found th at the C subtype protease has the highest vitality (4-11 higher than the B subtype) whereas the A subtype protease exhibits values ranging between 1.5 and 5. These results point to a higher biochemical fitness of the A and C proteases in the presence of existing inhibitors.