Conformational effects on tryptophan fluorescence in cyclic hexapeptides

Area of Science:

• Biochemistry
• Spectroscopy
• Structural Biology

Background:

• Tryptophan fluorescence is crucial for studying protein structure and dynamics.
• Peptide bonds are known quenchers of tryptophan fluorescence via excited-state electron transfer.
• Understanding factors influencing tryptophan fluorescence intensity is vital for biochemical analysis.

Purpose of the Study:

• To investigate the role of peptide bonds in quenching tryptophan fluorescence.
• To correlate peptide structure with tryptophan fluorescence properties.
• To elucidate how tryptophan's local environment affects its fluorescence decay.

Main Methods:

• Design and synthesis of seven peptides with single tryptophan residues.
• Determination of peptide solution structure and side-chain rotamer populations using 1D and 2D 1H-NMR.
• Measurement of fluorescence emission maxima, quantum yields, and fluorescence decay lifetimes.

Main Results:

• Peptide backbone conformation was consistent across all designed peptides.
• Tryptophan side-chain rotamer populations and backbone angles varied with sequence position.
• Fluorescence lifetimes were correlated with specific ground-state tryptophan conformers, with different rotamers exhibiting distinct lifetimes.

Conclusions:

• Peptide bond quenching is a dominant factor in determining tryptophan fluorescence intensity in peptides.
• Local backbone conformation and tryptophan side-chain rotameric state significantly influence fluorescence lifetimes.
• NMR-derived structural data provides insights into the molecular basis of fluorescence quenching mechanisms.