title: The surface protein Shr of Streptococcus pyogenes binds heme and transfers it to the streptococcal heme-binding protein Shp.
abstract: BACKGROUND
  The heme acquisition machinery in Streptococcus pyogenes is believed to consist of the surface proteins, Shr and Shp, and heme-specific ATP-binding cassette transporter HtsABC. Shp has been shown to rapidly transfer its heme to the lipoprotein component, HtsA, of HtsABC. The function of Shr and the heme source of Shp have not been established.
  
  
  RESULTS
  The objective of this study was to determine whether Shr binds heme and is a heme source of Shp. To achieve the objective, recombinant Shr protein was prepared. The purified Shr displays a spectrum typical of hemoproteins, indicating that Shr binds heme and acquires heme from Escherichia coli hemoproteins in vivo. Spectral analysis of Shr and Shp isolated from a mixture of Shr and heme-free Shp (apoShp) indicates that Shr and apoShp lost and gained heme, respectively; whereas Shr did not efficiently lose its heme in incubation with apoHtsA under the identical conditions. These results suggest that Shr directly transfers its heme to Shp. In addition, the rates of heme transfer from human hemoglobin to apoShp are close to those of simple ferric heme dissociation from hemoglobin, suggesting that methemoglobin does not directly transfer its heme to apoShp.
  
  
  CONCLUSIONS
  We have demonstrated that recombinant Shr can acquire heme from E. coli hemoproteins in vivo and appears to directly transfer its heme to Shp and that Shp appears not to directly acquire heme from human methemoglobin. These results suggest the possibility that Shr is a source of heme for Shp and that the Shr-to-Shp heme transfer is a step of the heme acquisition process in S. pyogenes. Further characterization of the Shr/Shp/HtsA system would advance our understanding of the mechanism of heme acquisition in S. pyogenes.
authors.affiliation: Department of Veterinary Molecular Biology, Montana State University, Bozeman, Montana 59717, USA. dzhuhui@yahoo.com.cn
authors.forename: Hui
authors.initials: H
authors.lastname: Zhu
authors.forename: Mengyao
authors.initials: M
authors.lastname: Liu
authors.forename: Benfang
authors.initials: B
authors.lastname: Lei
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D002352:Carrier Proteins / Q000378:metabolism*; D006418:Heme / Q000378:metabolism*; D000081062:Heme-Binding Proteins; D006420:Hemeproteins / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D013297:Streptococcus pyogenes / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D000081062:Heme-Binding Proteins; D006420:Hemeproteins; D011994:Recombinant Proteins; D006418:Heme