Fluorescence dynamics of LicT protein by time-resolved spectroscopy

In this paper, the fluorescence dynamics of tryptophan residues in LicT protein is investigated by time-resolved fluorescence method combined with UV absorption and steady-state fluorescence spectroscopy. The local microenvironment and structural changes of LicT protein before and after activation are studied. The activated LicT protein AC 141 prevents the antitermination of gene transcription involved in carbohydrate utilization to accelerate the body′s metabolism. The structural properties and microenvironment of activated protein AC 141 and wild-type protein Q 22 were determined by different fluorescence emissions and lifetimes of tryptophan residues. The interaction between tryptophan residues and solvent is elucidated by decay associated spectroscopy (DAS) and time-resolved emission spectra (TRES), indicating that upon activation, the structure of AC 141 is more compact than that of wild-type Q 22. In addition, TRES also showed that tryptophan residues in the protein had a continuous spectral relaxation process. Anisotropy results illustrated the conformational motions of residues and whole proteins, suggesting that tryptophan residues had independent local motions in the protein system, and that the motions were more intense in the activated protein.