Passage of Heme-Iron Across the Envelope of Staphylococcus aureus

The cell wall envelope of Gram-positive pathogens functions as a scaffold for the attachment of virulence factors and as a sieve that prevents diffusion of molecules. Here the isd genes (iron-regulated surface determinant) of Staphylococcus aureus were found to encode factors responsible for hemoglobin binding and passage of heme-iron to the cytoplasm, where it acts as an essential nutrient. Heme-iron passage required two sortases that tether Isd proteins to unique locations within the cell wall. Thus, Isd appears to act as an import apparatus that uses cell wall–anchored proteins to relay heme-iron across the bacterial envelope.