Neisseria acquires iron by extracting it from serum transferrin (TF) in its human host. Acts as a TF receptor and is required for TF utilization. Binds both apo- and holo-TF, via the TF C-terminus. Binds both human apo- and holo-transferrin (TF), via the TF C-terminus. Forms a large complex with TF and TbpB. By iron starvation. N.meningitidis cells will only bind to human TF, not bovine or porcine TF, explaining at least in part the bacteria's inability to cause infection in non-human hosts. Belongs to the TonB-dependent receptor family.