Brucella outer membrane protein Omp31 is a haemin-binding protein

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Iron Metabolism

Background:

• Gram-negative bacteria utilize outer membrane haemin-binding proteins (HBPs) for iron acquisition from hosts.
• Brucella species lack described HBPs, posing a challenge for understanding their iron uptake mechanisms.

Purpose of the Study:

• To determine if Brucella outer membrane protein Omp31 functions as a haemin-binding protein (HBP).
• To investigate the iron-regulation of Omp31 expression in Brucella.

Main Methods:

• Recombinant Omp31 and native Omp31 from Brucella membrane fractions were tested for haemin binding using agarose assays and Western blotting.
• Recombinant Escherichia coli expressing Omp31 were used to assess haemin binding in a bacterial membrane environment.
• Antibody inhibition assays with Brucella ovis cells were performed to confirm Omp31's role as an HBP.
• Western blot analysis was used to assess Omp31 expression levels under iron-replete and iron-depleted conditions.

Main Results:

• Soluble and membrane-bound Omp31 specifically bound haemin.
• Omp31 expressed on Escherichia coli membranes enhanced haemin binding.
• Antibodies against Omp31 inhibited haemin binding to Brucella ovis cells.
• Omp31 expression was significantly upregulated in Brucella suis grown under iron-limiting conditions.

Conclusions:

• Omp31 functions as a haemin-binding protein (HBP) in Brucella species, facilitating iron uptake.
• The expression of Omp31 is induced by iron limitation, suggesting a role in bacterial adaptation to low-iron environments.