Cell wall-anchored surface receptor that participates in the extraction of heme from oxidized methemoglobin/metHb to enable growth on hemoglobin as a sole iron source (By similarity). Receives heme from IsdB and transfers it to IsdC (PubMed:18184657). Also plays a role in the inhibition of host immune response (PubMed:18097052). Protects S.aureus against the bactericidal protease activity of apolactoferrin. Decreases bacterial cellular hydrophobicity, which renders S.aureus resistant to bactericidal human skin fatty acids as well as to beta-defensins and cathelicidin. Also binds fibronectin and chains B-beta and gamma of fibrinogen, promoting clumping of S.aureus with fibrinogen. Involved in adherence of S.aureus to human desquamated nasal epithelial cells and is required for nasal colonization (By similarity) (PubMed:18184657, PubMed:18097052). Monomer. Interacts with IsdC (PubMed:18184657). Interacts with IsdB (By similarity). Encodes an LPXTG motif-containing sorting signal that targets to the cell wall, which is catalyzed by sortase A. Repressed by fur in the presence of iron (By similarity). Transcriptionally up-regulated by hydrogen peroxide. The NEAT domain is responsible for binding Fe(3+) and Fe(2+) heme and fibrinogen. The NEAT domain is an inhibitor of apolactoferrin activity, while the C-domain confers resistance to bovine lactoferricin (By similarity). A combined vaccine containing IsdA, IsdB, SdrD and SdrE afforded significant protection in mice against a lethal challenge with S.aureus Newman or any of the clinical isolates NRS252, N315, NRS248, USA100 and USA400. The immune response elicited by the combined vaccine is greater than the one elicited by its individual components. Belongs to the IsdA family.