Connecting lipoxygenase function to structure by electron paramagnetic resonance

Area of Science:

• Biochemistry
• Enzymology
• Structural Biology

Background:

• Lipoxygenases catalyze oxygen insertion into polyunsaturated lipids, producing hydroperoxides.
• Despite conserved protein folds across species, the mechanism of specificity in lipoxygenase reactions remains a puzzle.
• Lipoxygenase active sites contain a catalytic metal, typically iron, within a protein shell accommodating the lipid substrate.

Purpose of the Study:

• To bridge the gap between solution-based lipid-lipoxygenase interactions and crystal structure data.
• To elucidate the structural and dynamic aspects governing lipoxygenase specificity and catalysis.
• To investigate the conserved geometry of lipoxygenase iron centers using electron paramagnetic resonance (EPR) spectroscopy.

Main Methods:

• Electron paramagnetic resonance (EPR) spectroscopy, including pulsed dipolar EPR, was employed.
• Experiments utilized spin-labeled lipids to probe lipid binding and accessibility within the active site.
• Spin-labeled protein mutants were used to study substrate/product dynamics and iron center characterization.

Main Results:

• Bound lipids are tethered by their acyl chain, with flexible polar headgroups exposed to solvent.
• Pulsed, dipolar EPR measurements determined the precise location of spin labels on bound lipids.
• EPR spectral comparisons suggest a conserved geometry of iron centers in plant and bacterial lipoxygenases.

Conclusions:

• EPR spectroscopy provides crucial insights into lipoxygenase structure-function relationships in solution.
• The findings illuminate how enzyme structure dictates specificity in lipid oxygenation reactions.
• Established and emerging EPR techniques are valuable tools for studying the lipoxygenase enzyme family.