Cooperation between the components of the meningococcal transferrin receptor, TbpA and TbpB, in the uptake of transferrin iron by the 37-kDa ferric-binding protein (FbpA).

Meningococcal TbpAB complexes TbpA, TbpB and FbpA were purified and used to study their role in the uptake of iron from transferrin to FbpA. Purification was achieved by affinity chromatography techniques, yielding homogeneous, non-denatured and functional material. TbpA could not be separated from TbpB and had to be purified from a TbpB-defective mutant strain. FbpA was able to bind iron from transferrin only when TbpAB complexes, TbpA and/or TbpB, were also present during the interaction. The highest uptake efficiences were obtained with TbpAB complexes or TbpA/TbpB mixtures. We conclude that the TbpA and TbpB molecules form true functional transferrin receptors, that FbpA is able to take iron directly from transferrin when in the presence of the components of the receptor, and that both Tbps are necessary for an optimal operation of the uptake system.