A fluorescence study of Tn10-encoded tet repressor

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• The Tet repressor from Escherichia coli is a homodimeric protein crucial for regulating tetracycline resistance.
• Understanding the dynamics and microenvironment of tryptophan residues provides insights into protein structure and function.
• Tryptophan residues W43 and W75 are key sites for investigating Tet repressor's conformational states and ligand interactions.

Purpose of the Study:

• To resolve and characterize the distinct fluorescence contributions of W43 and W75 tryptophan residues in Tet repressor.
• To investigate the role of these residues in the protein's structure, dynamics, and conformational states.
• To confirm residue assignments using site-specific mutagenesis and advanced spectroscopic techniques.

Main Methods:

• Steady-state fluorescence quenching and time-resolved fluorescence measurements.
• Fluorescence-Quenching-Resolved-Spectra (FQRS) method for spectral decomposition.
• Site-specific mutagenesis to create single-tryptophan mutants (W43 and W75).

Main Results:

• Resolved spectra showed fluorescence maxima at 349 nm (W43) and 324 nm (W75), consistent with mutant data.
• W43 exhibited two emission components: a solvent-exposed, quenchable component and an unquenchable component.
• W75 fluorescence quenching indicated it is not deeply buried within the protein matrix.

Conclusions:

• Tet repressor exists in at least two distinct ground-state conformational states, differentiated by the W43 microenvironment.
• The W75 residue's accessibility suggests its involvement in conformational changes related to tetracycline binding.
• Spectroscopic analysis provides a detailed understanding of Tet repressor's structural dynamics and functional states.