Deciphering the role of neutral diruthenium complexes in protein binding

Area of Science:

• Coordination Chemistry
• Biophysical Chemistry
• Protein-Ligand Interactions

Background:

• The charge of paddlewheel diruthenium complexes dictates their protein binding modes: anionic complexes bind non-covalently, while cationic complexes coordinate to specific amino acid residues or backbone sites.
• Neutral diruthenium complexes represent a rare class with limited investigation into their protein interactions.

Purpose of the Study:

• To investigate the interaction of a neutral diruthenium compound, [Ru2(D-p-FPhF)(O2CCH3)2(O2CO)]·3H2O, with the model protein bovine pancreatic ribonuclease (RNase A).
• To elucidate the binding sites and structural consequences of neutral diruthenium-protein complex formation.

Main Methods:

• UV-visible absorption spectroscopy
• Circular dichroism (CD)
• Electrospray ionization mass spectrometry (ESI-MS)
• X-ray crystallography

Main Results:

• ESI-MS revealed that the diruthenium compound binds RNase A with the loss of an acetate ligand in solution.
• X-ray crystallography identified binding to the imidazole ring of His105 at an axial site, with acetate replaced by water molecules.
• The side chains of Glu9 and His119 were also identified as potential binding sites, and protein aggregation was significantly affected.

Conclusions:

• Glutamate (Glu) side chains should be considered as potential binding sites for diruthenium compounds.
• Diruthenium-containing fragments, potentially unstable in solution, can be stabilized through protein interactions.
• Neutral diruthenium compounds show potential as modulators of protein aggregation.