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. Involved in the initial capture of TF. Helps select only those TF molecules that can be used as an iron source and concentrates them on the cell surface, maintaining the iron-loaded status of the TF C-terminal lobe until its delivery to TbpA. Binds only human holo-transferrin (TF), via the TF C-terminus. Forms a large complex with TF and TbpA (By similarity). Interacts via its C-terminal domain with Slam1 (PubMed:27572441). By iron starvation. Has 2 lobes, each of which has an 8-strand beta barrel flanked on their N-terminus by a 4-strand handle domain. 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 TbpB family. Isotype I subfamily.