Fluorescence Labeling of Peptides: Finding the Optimal Protocol for Coupling Various Dyes to ATCUN-like Structures

Area of Science:

• Bioconjugation Chemistry
• Fluorescent Probes
• Peptide Synthesis

Background:

• Fluorescent labeling of peptides and proteins is essential for various biological assays.
• Current dye coupling strategies often lack optimization, leading to inefficiency and high costs.
• Amino-terminal Cu(II) and Ni(II) binding site (ATCUN) peptides serve as a model system for studying labeling methods.

Purpose of the Study:

• To identify optimal conditions for attaching common fluorescent dyes (6-carboxyfluorescein, Rhodamine B, BODIPY-FL) to peptides.
• To develop improved labeling strategies for both primary and secondary amines on peptides.
• To apply fluorescently labeled ATCUN peptides for metal ion sensing and optimize dye-peptide conjugation for this application.

Main Methods:

• Investigated conventional and novel dye attachment methods for peptides.
• Utilized microwave irradiation to expedite the synthesis of activated pentafluorophenol (PFP) esters for primary amine labeling.
• Employed standard coupling reagents like HATU and PyBOP for secondary amine labeling.
• Incorporated fluorescently labeled ATCUN peptides into Cu(II) and Ni(II) sensing assays.

Main Results:

• Conventional dye attachment methods yielded poor efficiency.
• Activated PFP esters, accelerated by microwave irradiation, proved most effective for labeling primary amines.
• HATU and PyBOP were efficient for labeling secondary amines.
• Fluorescent dye choice did not significantly impact fluorescence quenching in metal ion sensing.
• Optimal linker length between the ATCUN core and the dye was determined.

Conclusions:

• Activated PFP esters with microwave irradiation represent a highly efficient strategy for labeling primary amines on peptides.
• Established efficient methods for labeling both primary and secondary amines, enhancing peptide functionalization.
• Demonstrated the utility of fluorescently labeled ATCUN peptides for metal ion sensing, expanding fluorophore options and optimizing probe design.