Hemin-binding surface protein from Bartonella quintana.

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Molecular Biology

Background:

• Bartonella quintana causes trench fever, endocarditis, and bacillary angiomatosis.
• B. quintana exhibits an exceptionally high in vitro hemin requirement.
• Hemin acquisition is crucial for bacterial survival and virulence.

Purpose of the Study:

• To identify and characterize hemin-binding proteins in Bartonella quintana.
• To investigate the role of the dominant hemin-binding protein in B. quintana pathogenesis.
• To determine the location and genetic basis of the primary hemin-binding protein.

Main Methods:

• Triton X-114 extraction and heat modification assays to characterize membrane proteins.
• Immunoblotting and immunoelectron microscopy to determine protein localization.
• Gene cloning, sequencing, and recombinant protein expression to analyze the hbpA gene and protein.
• Southern blotting to assess the presence of hbpA homologs in other Bartonella species.
• Functional assays using anti-HbpA Fab fragments to evaluate hemin binding.

Main Results:

• Eight membrane proteins bind hemin, with HbpA (approximately 25 kDa) being dominant.
• HbpA is an outer membrane protein, surface-exposed, and heat-modifiable.
• The hbpA gene was cloned and sequenced, revealing a Fur box homolog upstream.
• HbpA homologs are present in all five pathogenic Bartonella species.
• Antibody inhibition of HbpA significantly reduced hemin binding, confirming its role in acquisition.

Conclusions:

• HbpA is the primary hemin-binding protein in Bartonella quintana.
• HbpA is a surface-exposed outer membrane protein crucial for hemin acquisition.
• HbpA represents the first characterized virulence determinant of Bartonella quintana and a potential therapeutic target.