Dynamics ofLens culinaris agglutinin studied by red-edge excitation spectra and anisotropy measurements of 2-p-toluidinylnaphthalene-6-sulfonate (TNS) and of tryptophan residues

Abstract

The fluorescence of 2-p-toluidinylnaphthalene-6-sulfonate bound toLens culinaris agglutinin and of the Trp residues of the protein was investigated. Red-edge excitation spectra and steady-state anisotropy as a function of temperature indicate that the TNS is bound rigidly. Red-edge excitation spectra, steady-state anisotropy as a function of sucrose and anisotropy decay experiments performed on Trp residues fluorescence prove that the internal fluorophore presents residual motion independent of the global rotation of the protein. Fluorescence anisotropy decay allows to calculate the rotational correlation time (351 ps) of this local motion. Quenching resolved emission anisotropy with iodide gives values equal to 0.257 and 0.112 for the anisotropies of the buried and the surface Trp residues, respectively. This result indicates that the Trp residues present at the surface of the protein have important local motions compared to those embedded in the protein matrix. The results obtained from TNS and Trp residues indicate that the agglutinin has different dynamic domains.