The nutrient iron is essential for bacterial growth and infection. Pathogenic bacteria have evolved multiple mechanisms for acquiring iron from the infected host. The iron regulated surface determinant (Isd) pathway of Staphylococcus aureus is highly up-regulated during infection and targets the largest mammalian pool of iron, the haem protein, haemoglobin A (Hb). The Isd system contains nine proteins that capture Hb on the cell surface, liberate the haem cofactor and relay it through the cell wall and membrane into the cytoplasm where it is degraded, releasing iron. Two related proteins IsdB and IsdH are expressed on the bacterial cell-surface where they act as receptors for HbA and extract the haem molecule from the host protein. Both Hb and the isolated haem ligand are bound by near iron-transport (NEAT) domains, which are found in multiple copies in IsdB and IsdH. It is the combination of NEAT domains in full-length proteins that allows for rapid haem removal from Hb, as the isolated NEAT domains do not retain this function. While the structures of the individual NEAT domains have been determined the mechanism of haem transfer to the Isd proteins is still unexplained. We aim to understand how domains cooperate to achieve rapid haem transfer. We have determined the structure of IsdH bound to Hb, and shown that no large changes in the globin structure occur. Instead the haem binding NEAT domains of IsdH make direct contacts with the haem pockets of Hb. IsdH is positioned to access all four haem groups carried by one Hb molecule. However, X-ray and light scattering experiments predict that haem will be preferentially removed from the alpha subunit of Hb. To confirm this mechanism, UV-visible absorption spectroscopy, and mass spec are currently being used to track the transfer of haem within the complex.