Gonococcal transferrin-binding protein 2 facilitates but is not essential for transferrin utilization

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Pathogenesis

Background:

• Pathogenic Neisseria species, including Neisseria gonorrhoeae, require iron for growth and can acquire it from human transferrin (Tf).
• Two iron-repressible proteins, Tbp1 and Tbp2, have been identified with transferrin-binding activity, but their specific roles in iron acquisition remain unclear.

Purpose of the Study:

• To clone and sequence the gene encoding Tbp2 (tbpB) in Neisseria gonorrhoeae.
• To elucidate the roles of Tbp1 and Tbp2 in transferrin binding and iron uptake by N. gonorrhoeae.

Main Methods:

• Cloning and sequencing of the tbpB gene.
• Construction and analysis of N. gonorrhoeae mutants with targeted deletions or interruptions in tbpB and tbpA.
• Assessment of transferrin binding, iron uptake, and growth on transferrin-containing media.

Main Results:

• The tbpB gene encodes Tbp2, an 85-kDa iron-repressible lipoprotein.
• Transcriptional interruption of tbpB affected the expression of the downstream gene tbpA, encoding Tbp1.
• Mutants lacking Tbp2 showed reduced Tf binding and iron uptake but retained growth on Tf plates, suggesting Tbp1 is crucial for iron acquisition.
• Mutants lacking Tbp1 exhibited significantly impaired Tf binding, iron uptake, and growth on Tf plates.

Conclusions:

• The tbpB and tbpA genes are likely organized in a polycistronic operon.
• Tbp2 facilitates transferrin binding, but Tbp1 is essential for efficient iron acquisition from transferrin in N. gonorrhoeae under the tested conditions.