Acts as a receptor for hemoglobin or the hemoglobin/haptoglobin complex of the human host and is required for heme uptake. This protein is subject to phase-variable expression associated with alteration in the length of the CCAA repeat region. This mechanism is called slipped-strand mispairing. Addition or loss of CCAA repeat units would change the reading frame and result in introduction of stop codons downstream of the repeat region. This may be a mechanism of regulation and a way to avoid the immunological response of the host (By similarity). Belongs to the TonB-dependent receptor family. Hemoglobin/haptoglobin binding protein subfamily. The first frameshift is found in the repeats region. The first frameshift is found in the repeats region.