An oxygenation-sensitive dye binding to Carcinus maenas hemocyanin

Area of Science:

• Biophysical Chemistry
• Protein-Ligand Interactions
• Spectroscopy

Background:

• Hemocyanin is a copper-containing protein responsible for oxygen transport in many invertebrates.
• Understanding hemocyanin's structure-function relationship, particularly oxygen binding, is crucial.
• Fluorescent probes can offer insights into protein dynamics and ligand interactions.

Purpose of the Study:

• To investigate the interaction between the fluorescent dye 4',6-diamidino-2-phenylindole (DAPI) and Carcinus maenas hemocyanin.
• To determine if DAPI can serve as a functional probe for monitoring oxygen binding to hemocyanin.
• To elucidate the structural changes in hemocyanin upon oxygenation using DAPI as a reporter.

Main Methods:

• Steady-state and dynamic fluorescence spectroscopy.
• Circular dichroism measurements.
• Analysis of DAPI binding affinity and fluorescence properties with different hemocyanin forms (apo, deoxygenated, oxygenated).

Main Results:

• DAPI binds to apo-, deoxygenated, and oxygenated hemocyanin with similar affinities and stoichiometry.
• DAPI exhibits significantly lower fluorescence quantum yield enhancement when bound to oxygenated hemocyanin compared to other forms.
• Changes in DAPI fluorescence correlate with oxygen partial pressure and hemocyanin's copper-oxygen charge transfer band, suggesting DAPI as a potential oxygenation probe.

Conclusions:

• The fluorescence behavior of DAPI is sensitive to the oxygenation state of hemocyanin, likely due to conformational changes.
• DAPI's distinct fluorescence decay kinetics with oxygenated hemocyanin suggest differential interactions with protein rotamers.
• DAPI serves as a valuable functional probe for studying the cooperative oxygen binding and structural dynamics of hemocyanin.