TIME-RESOLVED FLUORESCENCE ANISOTROPY OF HIV-1 PROTEASE INHIBITOR COMPLEXES CORRELATES WITH INHIBITORY ACTIVITY

The tryptophan time-resolved fluorescence intensity and anisotropy of the HIV-1 protease dimer is shown to be a quick and efficient method f or the conformational characterization of protease inhibitor complexes . Four fluorescence lifetimes were needed to adequately describe the f luorescence decay of the two tryptophan residues, W6 and W42, per prot ease monomer. As a result of the wavelength dependence of the respecti ve amplitudes, the 2.06 ns and the 4.46 ns decay constants were sugges ted to be the intrinsic fluorescence lifetimes of the more solvent-exp osed W6 and the less exposed W42 residues, respectively. Analysis of t he fluorescence anisotropy decay yielded a short correlation time of 2 50 ps corresponding to local chromophore motions, and a long correlati on time of 12.96 ns resulting from overall rotation of the protease en zyme. Fluorescence lifetimes and rotational correlation times changed when inhibitors of the HIV-1 protease were added. The effects of 11 di fferent inhibitors including statine-derived, hydroxyethylamine-derive d, and 2 symmetrical inhibitors on the protease fluorescence dynamics were investigated. Inhibitor binding is shown to induce an increase of the mean fluorescence lifetime tau(mean), an increase of the short ro tational correlation time phi(1), as well as a decrease of the long ro tational correlation time phi(2). The mean rotational correlation time phi(mean) was identified as the global dynamic parameter for a given molecular complex, which correlates with the inhibitor dissociation co nstant K-i, and therefore with the activity of the inhibitor.