Exciplex Formation in Lipid-bound Escherichia coli Flavohemoglobin

Area of Science:

• Biochemistry
• Protein-lipid interactions
• Spectroscopy

Background:

• Flavohemoglobins (FHbs) exhibit unique fatty acid binding capabilities.
• Lipid binding affects the electronic and dynamic properties of the heme iron.

Purpose of the Study:

• To investigate the interaction between fatty acids and the heme iron in FHbs.
• To characterize the influence of lipid binding on protein dynamics and electronic states.

Main Methods:

• Transient absorption spectroscopy was employed.
• Measurements were performed on ferrous and ferric FHb, with and without bound lipids.
• Excitation of deoxygenated and CO-bound protein derivatives was analyzed.

Main Results:

• Fatty acid binding induces a weak interaction with ferric heme.
• A slow relaxation process (350 ps) was observed in lipid-bound protein upon excitation, absent in lipid-free protein.
• Evidence suggests a charge-transfer complex formation in the excited state, involving the heme iron and lipid acyl chain.
• Lipid presence inhibits CO mobility in the heme pocket, reducing geminate rebinding.

Conclusions:

• Lipid binding modulates FHb electronic and dynamic properties, particularly in excited states.
• A long-range interaction between the heme iron and lipid acyl chain occurs in the excited state.
• Lipid association impacts heme pocket accessibility and ligand dynamics.