Modification of lactoferrin by peroxynitrite reduces its antibacterial activity and changes protein structure

Area of Science:

• Biochemistry
• Immunology
• Protein Chemistry

Background:

• Lactoferrin (LF) is a vital protein in mammalian fluids, offering antibacterial properties and protection against oxidative stress via iron binding.
• Biologically relevant mediators like peroxynitrite (ONOO-) can modify LF, particularly during inflammation and nitrosative stress.

Purpose of the Study:

• To investigate the structural and functional consequences of lactoferrin nitration by peroxynitrite (ONOO-).
• To assess the impact of nitration on LF's antibacterial activity, iron-binding capacity, and secondary structure.

Main Methods:

• Treatment of LF with peroxynitrite (ONOO-) at a 10:1 molar ratio.
• Assessment of antibacterial activity.
• Circular dichroism spectroscopy for secondary structure analysis.
• Liquid chromatography-tandem mass spectrometry (LC-MS/MS) for identifying nitrated peptides.

Main Results:

• Nitration by ONOO- completely abolished the antibacterial activity of LF.
• Significant reduction in alpha-helical content was observed, indicating partial protein unfolding.
• Iron-binding capacity of nitrated LF was decreased, with Y92 identified as a nitrated residue in the iron-binding region.

Conclusions:

• Post-translational modification of LF by ONOO- impairs its antibacterial and iron-binding functions.
• Nitrated LF exhibits reduced structural integrity and diminished capacity to protect against cellular damage.
• These modifications may exacerbate infections in inflamed tissues by compromising LF's immune response capabilities.