Haemophilus influenzae stores and distributes hemin by using protein E.

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Haemophilus influenzae is a human pathogen causing respiratory infections.
• Protein E (PE) is a multifunctional adhesin involved in host cell interactions.
• The crystal structure of PE suggested a potential hemin-binding pocket.

Purpose of the Study:

• To investigate the interaction between H. influenzae protein E (PE) and hemin.
• To determine if PE facilitates hemin uptake and sharing in H. influenzae.

Main Methods:

• Construction and analysis of H. influenzae mutants lacking PE.
• Expression of PE on the surface of E. coli to assess hemin binding.
• Biochemical assays including native-PAGE and UV-visible spectrophotometry.
• Surface plasmon resonance (SPR) to quantify the hemin-PE interaction affinity.
• Co-culture experiments to observe hemin transfer between H. influenzae strains.

Main Results:

• H. influenzae mutants lacking PE showed reduced hemin binding.
• E. coli expressing PE on its surface exhibited a hemin-binding phenotype.
• Direct interaction between hemin and recombinant soluble PE was confirmed.
• SPR analysis revealed a dissociation constant (Kd) of 1.6 × 10⁻⁶ M for the hemin-PE interaction.
• Bound hemin on PE was successfully donated to hemin-starved H. influenzae.

Conclusions:

• H. influenzae protein E (PE) directly binds hemin.
• PE functions as a hemin storage and transport protein for H. influenzae.
• This is the first report of hemin sharing mediated by a surface protein in H. influenzae.