title: Time-resolved fluorescence anisotropy of HIV-1 protease inhibitor complexes correlates with inhibitory activity.
abstract: The tryptophan time-resolved fluorescence intensity and anisotropy of the HIV-1 protease dimer is shown to be a quick and efficient method for the conformational characterization of protease inhibitor complexes. Four fluorescence lifetimes were needed to adequately describe the fluorescence decay of the two tryptophan residues, W6 and W42, per protease monomer. As a result of the wavelength dependence of the respective amplitudes, the 2.06 ns and the 4.46 ns decay constants were suggested to be the intrinsic fluorescence lifetimes of the more solvent-exposed W6 and the less exposed W42 residues, respectively. Analysis of the fluorescence anisotropy decay yielded a short correlation time of 250 ps corresponding to local chromophore motions, and a long correlation time of 12.96 ns resulting from overall rotation of the protease enzyme. Fluorescence lifetimes and rotational correlation times changed when inhibitors of the HIV-1 protease were added. The effects of 11 different inhibitors including statine-derived, hydroxyethylamine-derived, and 2 symmetrical inhibitors on the protease fluorescence dynamics were investigated. Inhibitor binding is shown to induce an increase of the mean fluorescence lifetime taumean, an increase of the short rotational correlation time phi1, as well as a decrease of the long rotational correlation time phi2. The mean rotational correlation time phimean was identified as the global dynamic parameter for a given molecular complex, which correlates with the inhibitor dissociation constant Ki, and therefore with the activity of the inhibitor.
authors.affiliation: Department of Immunology, Novartis Forschungsinstitut, Brunnerstrasse 59, A-1235 Wien, Austria. andreas.kungl@pharma.novartis.com
authors.forename: A J
authors.initials: AJ
authors.lastname: Kungl
authors.forename: N V
authors.initials: NV
authors.lastname: Visser
authors.forename: A
authors.initials: A
authors.lastname: van Hoek
authors.forename: A J
authors.initials: AJ
authors.lastname: Visser
authors.forename: A
authors.initials: A
authors.lastname: Billich
authors.forename: A
authors.initials: A
authors.lastname: Schilk
authors.forename: H
authors.initials: H
authors.lastname: Gstach
authors.forename: M
authors.initials: M
authors.lastname: Auer
mesh_terms: D005454:Fluorescence Polarization; D016333:HIV Protease / Q000737:chemistry*; D017320:HIV Protease Inhibitors / Q000737:chemistry*; D007700:Kinetics; D008958:Models, Molecular; D011487:Protein Conformation
chemical_list: D017320:HIV Protease Inhibitors; D016333:HIV Protease