Free iron is limited in vertebrate hosts, thus an alternative to siderophores has been developed by pathogenic bacteria to access host iron bound in protein complexes. HasA is a secreted hemophore that has the ability to obtain iron from hemoglobin. Once bound to HasA, the heme is shuttled to the receptor HasR, which releases the heme into the bacterium [1].

1: The crystal structure of HasA, a hemophore secreted by Serratia marcescens. Arnoux P, Haser R, Izadi N, Lecroisey A, Delepierre M, Wandersman C, Czjzek M; Nat Struct Biol 1999;6:516-520. PMID:10360351