Insight into blocking heme transfer by exploiting molecular interactions in the core Isd heme transporters IsdA-NEAT, IsdC-NEAT, and IsdE of Staphylococcus aureus

The pathogenic bacterium Staphylococcus aureus has adopted specialized mechanisms for scavenging iron from its host. The nine cell wall and membrane-associated iron regulated surface determinant (Isd) proteins (IsdH, IsdB, IsdA, IsdC, IsdDEF, IsdG and IsdI) allow Staphylococcus aureus to scavenge iron from the heme in hemoglobin and haptoglobin-hemoglobin. Of these, it is IsdE that chaperones the heme to the ATP binding cassette-type transmembrane transporter (IsdF). IsdH, IsdB, IsdA and IsdC contain at least one heme binding Near Transporter (NEAT) domain. Previous studies have shown that ferric heme is transferred unidirectionally in the sequence IsdA-NEAT (Tyr - proximal amino acid) → IsdC-NEAT (Tyr) → IsdE (His). IsdA-NEAT does not transfer heme directly to IsdE. In this paper we investigated PPIX transfer through the core cell wall proteins of the Isd system (IsdA-NEAT, IsdC-NEAT and IsdE) with FePPIX-dimethylester, and the metal substituted CoPPIX and MnPPIX using ESI-MS, UV-visible absorption and MCD spectroscopy. IsdA binds each of the rings but the subsequent transfer properties to IsdC-N or IsdE are not the same as found with heme. FePPIX-DME transfers from IsdA-N to IsdC-N but neither protein transfers the ring to IsdE. IsdA-N does not transfer CoPPIX to IsdC-N or IsdE. IsdA-N does transfer MnPPIX to both IsdC-N and IsdE. Significantly, it is possible that since CoPPIX and FePPIX-DME bind to IsdA-N, the lack of transfer to IsdC-N and subsequently to IsdE for CoPPIX could prove to be used as a potential disruption agent to the S. aureus heme transfer system and may identify a possible anti-microbial.