Tag Info: N-terminal 10xHis-tagged and C-terminal Myc-tagged. MW: 35.1 kDa. Function: Transfers its hemin to hemin-free IsdC (apo-IsdC) directly probably through the activated holo-IsdA-apo-IsdC complex and driven by the higher affinity of apo-IsdC for the cofactor. The reaction is reversible. Binds transferrin, lactoferrin, heme, hemoglobin, hemin, fetuin, asialofetuin and protein A. Also binds fibronectin and chains B-beta and gamma of fibrinogen. Could play a role in the removal of heme from hemoglobin. The IsdA-mediated iron-acquisition system from transferrin could play only an ancillary role in the iron uptake whereas the siderophore-mediated iron-acquisition system from transferrin seems to play an essential or dominant role. May function as a reservoir for heme. Involved in adherence of S.aureus to human desquamated nasal epithelial cells and is required for nasal colonization. Protects S.aureus against the bactericidal protease activity of apolactoferrin in vitro and confers resistance to bovine lactoferricin. Also IsdA and/or IsdB promote resistance to hydrogen peroxide and killing by neutrophils (By similarity). Subcellular Location: Secreted, cell wall, Peptidoglycan-anchor.