Isd proteins are iron-regulated surface proteins found in Bacillus, Staphylococcus and Listeria species and are responsible for heme scavenging from hemoproteins. The IsdB protein is only observed in Staphylococcus and consists of an N-terminal hydrophobic signal sequence, a pair of tandem NEAT (NEAr Transporter, pfam05031) domains, which confers the ability to bind heme, and a C-terminal sortase processing signal which targets the protein to the cell wall. IsdB is believed to make a direct contact with methemoglobin facilitating transfer of heme to IsdB. The heme is then transferred to other cell wall-bound NEAT domain proteins such as IsdA and IsdC.
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