Subunit-selective mutagenesis of Glu-89 residue in human immunodeficiency virus reverse transcriptase. Contribution of p66 and p51 subunits to nucleoside analog sensitivity, divalent cation preference, and steady state kinetic properties

The E89G alteration in the human immunodeficiency virus type 1 reverse transcriptase has been shown to confer resistance to nucleoside analogs and a loss of magnesium cation preference (Prasad, V. R., Lowy, I., De Los Santos, T., Chiang, L., and Goff, S. P. (1991) Proc. Natl. Acad. Sci. U. S. A. 88, 11363-11367. The wild type reverse transcriptase heterodimer, chimeric reverse transcriptases that contain the E89G alteration in one of the subunits (p66^wt/p51^m and p66^m/p51^wt), and the mutant enzyme (p66^m/p51^m) were prepared. Analysis of steady state kinetic parameters showed that the mutant enzyme (p66^m/p51^m) displayed a higher V_max, a higher K_m for 2′-deoxythymidine triphosphate, and a higher K_i for 2′,3′-dideoxythymidine triphosphate than the wild type enzyme. The increased K_m and K_i values were observed only when a heterodimer contained the alteration in the p66 subunit. Tests for divalent cation requirement showed that only the dimers containing the wild type p66 (p66^wt/p51^wt and p66^wt/p51^m) displayed a preference for magnesium. Our results indicate that p66 plays a dominant role in deoxynucleotide triphosphate substrate recognition (K_m), nucleoside analog sensitivity (K_i), and magnesium preference. However, the increased V_max displayed by the mutant enzyme (p66^m/p51^m) appeared to be determined by both of the subunits.