The Major Outer Membrane Protein P5 Binds Vitronectin to Mediate Serum Resistance in Nontypeable Haemophilus...

Area of Science:

• Microbiology
• Immunology
• Molecular Biology

Background:

• Nontypeable Haemophilus influenzae (NTHi) employs virulence strategies to evade host immune responses, specifically complement-mediated killing.
• The NTHi outer membrane protein P5 is known to bind complement regulators like C4b-binding protein and factor H, contributing to serum resistance.

Purpose of the Study:

• To investigate the role of NTHi P5 protein in binding vitronectin.
• To determine if vitronectin binding by P5 contributes to NTHi serum resistance.

Main Methods:

• Heterologous surface expression of NTHi P5 variants in Escherichia coli.
• Deletion mutagenesis of the P5 gene (ompP5) in NTHi strains.
• Assessing vitronectin binding to bacterial strains.
• Evaluating serum resistance of bacteria expressing P5 or P5 deletion mutants.
• Site-directed mutagenesis to identify the vitronectin binding site on P5.

Main Results:

• NTHi P5 protein binds vitronectin, a complement inhibitor that targets the membrane attack complex.
• Surface expression of NTHi P5 on E. coli enhanced vitronectin binding.
• Deletion of P5 in NTHi strains reduced vitronectin binding.
• Vitronectin acquisition mediated serum resistance in P5-expressing E. coli but not in NTHi ΔompP5 mutants.
• Extracellular loop 2 of P5 was identified as the vitronectin binding site.

Conclusions:

• NTHi P5 acts as a direct receptor for human vitronectin.
• Vitronectin acquisition via P5 is a significant mechanism for NTHi to achieve serum resistance.
• Targeting the P5-vitronectin interaction could be a potential therapeutic strategy against NTHi infections.