Side-chain thioamides as fluorescence quenching probes.

Area of Science:

• Biochemistry and Molecular Biology
• Chemical Biology
• Protein Science

Background:

• Amide bonds are fundamental in proteins, influencing structure and function.
• Thioamides, as oxygen-to-sulfur substitutions, offer unique chemical properties.
• These properties make thioamides potential tools for studying protein dynamics and interactions.

Purpose of the Study:

• To investigate the fluorescence quenching characteristics of thioamides within amino acid side chains.
• To develop methods for incorporating thioamide-containing amino acids into peptides and proteins.
• To assess the utility of thioamides as probes in biochemical studies.

Main Methods:

• Synthesis of Fmoc-protected building blocks for N^ε-thioacetyl-lysine and γ-thioasparagine.
• Incorporation of these building blocks into model peptides using solid-phase peptide synthesis.
• Exploration of N^ε-thioacetyl-lysine incorporation into *Escherichia coli* proteins via amber codon suppression.

Main Results:

• Demonstrated distance-dependent fluorescence quenching of thioamides in rigid model peptides.
• Successfully synthesized and incorporated key thioamide-containing amino acid building blocks.
• Initiated efforts to integrate N^ε-thioacetyl-lysine into *E. coli* expressed proteins.

Conclusions:

• Thioamides exhibit predictable fluorescence quenching behavior, making them viable spectroscopic probes.
• The developed synthetic routes enable the incorporation of thioamides into peptides.
• Further research is warranted to fully establish thioamide incorporation into proteins for advanced biological studies.