Shr of group A streptococcus is a new type of composite NEAT protein involved in sequestering haem from methaemoglobin.
A growing body of evidence suggests that surface or secreted proteins with NEAr Transporter (NEAT) domains play a central role in haem acquisition and trafficking across the cell envelope of Gram-positive bacteria. Group A streptococcus (GAS), a β-haemolytic human pathogen, expresses a NEAT protein, Shr, which binds several haemoproteins and extracellular matrix (ECM) components. Shr is a complex, membrane-anchored protein, with a unique N-terminal domain (NTD) and two NEAT domains separated by a central leucine-rich repeat region. In this study we have carried out an analysis of the functional domains in Shr. We show that Shr obtains haem in solution and furthermore reduces the haem iron; this is the first report of haem reduction by a NEAT protein. More specifically, we demonstrate that both of the constituent NEAT domains of Shr are responsible for binding haem, although they are missing a critical tyrosine residue found in the ligand-binding pocket of other haem-binding NEAT domains. Further investigations show that a previously undescribed region within the Shr NTD interacts with methaemoglobin. Shr NEAT domains, however, do not contribute significantly to the binding of methaemoglobin but mediate binding to the ECM components fibronectin and laminin. A protein fragment containing the NTD plus the first NEAT domain was found to be sufficient to sequester haem directly from methaemoglobin. Correlating these in vitro findings to in vivo biological function, mutants analysis establishes the role of Shr in GAS growth with methaemoglobin as a sole source of iron, and indicates that at least one NEAT domain is necessary for the utilization of methaemoglobin. We suggest that Shr is the prototype of a new group of NEAT composite proteins involved in haem uptake found in pyogenic streptococci and Clostridium novyi.
Ouattara
Mahamoudou
M
Department of Biology,College of Arts and Sciences, Georgia State University, Atlanta, GA 30303, USA.
Cunha
Elizabeth Bentley
EB
Li
Xueru
X
Huang
Ya-Shu
YS
Dixon
Dabney
D
Eichenbaum
Zehava
Z
D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D001692:Biological Transport; D003013:Clostridium / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006418:Heme / Q000378:metabolism*; D006801:Humans; D008706:Methemoglobin / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013290:Streptococcal Infections / Q000378:metabolism / Q000382:microbiology*; D013297:Streptococcus pyogenes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D006418:Heme; D008706:Methemoglobin
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