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. Belongs to the TonB-dependent receptor family.