Identification and Characterization of HtsA, a Second Heme-Binding Protein Made byStreptococcus pyogenes

Group A streptococci (GAS) can use heme and hemoproteins as sources of iron. However, the machinery for heme acquisition in GAS has not been firmly revealed. Recently, we identified a novel heme-associated cell surface protein (Shp) made by GAS. Theshpgene is cotranscribed with eight downstream genes, includingspy1795,spy1794, andspy1793encoding a putative ABC transporter (designated HtsABC). In this study,spy1795(designatedhtsA) was cloned from a serotype M1 strain, and recombinant HtsA was overexpressed inEscherichia coliand purified to homogeneity. HtsA binds 1 heme molecule per molecule of protein. HtsA was produced in vitro and localized to the bacterial cell surface. GAS up-regulated transcription ofhtsAin human blood compared with that in Todd-Hewitt broth supplemented with 0.2% yeast extract. The level of thehtsAtranscript dramatically increased under metal cation-restricted conditions compared with that under metal cation-replete conditions. The cation content, cell surface location, and gene transcription of HtsA were also compared with those of MtsA and Spy0385, the lipoprotein components of two other putative iron acquisition ABC transporters of GAS. Our results suggest that HtsABC is an ABC transporter that may participate in heme acquisition in GAS.