title: Insight into the interaction of metal ions with TroA from Streptococcus suis.
abstract: BACKGROUND
  The scavenging ability of sufficient divalent metal ions is pivotal for pathogenic bacteria to survive in the host. ATP-binding cassette (ABC)-type metal transporters provide a considerable amount of different transition metals for bacterial growth. TroA is a substrate binding protein for uptake of multiple metal ions. However, the function and structure of the TroA homologue from the epidemic Streptococcus suis isolates (SsTroA) have not been characterized.
  
  
  RESULTS
  Here we determined the crystal structure of SsTroA from a highly pathogenic streptococcal toxic shock syndrome (STSS)-causing Streptococcus suis in complex with zinc. Inductively coupled plasma mass spectrometry (ICP-MS) analysis revealed that apo-SsTroA binds Zn(2+) and Mn(2+). Both metals bind to SsTroA with nanomolar affinity and stabilize the protein against thermal unfolding. Zn(2+) and Mn(2+) induce distinct conformational changes in SsTroA compared with the apo form as confirmed by both circular dichroism (CD) and nuclear magnetic resonance (NMR) spectra. NMR data also revealed that Zn(2+)/Mn(2+) bind to SsTroA in either the same site or an adjacent region. Finally, we found that the folding of the metal-bound protein is more compact than the corresponding apoprotein.
  
  
  CONCLUSIONS
  Our findings reveal a mechanism for uptake of metal ions in S. suis and this mechanism provides a reasonable explanation as to how SsTroA operates in metal transport.
authors: CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.
authors: Beiwen
authors: B
authors: Zheng
authors: Qiangmin
authors: Q
authors: Zhang
authors: Jia
authors: J
authors: Gao
authors: Huiming
authors: H
authors: Han
authors: Ming
authors: M
authors: Li
authors: Jingren
authors: J
authors: Zhang
authors: Jianxun
authors: J
authors: Qi
authors: Jinghua
authors: J
authors: Yan
authors: George F
authors: GF
authors: Gao
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