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Expression of the virulence‐related Sca (Mn 2+ ) permease in Streptococcus gordonii is regulated by a diphtheria toxin metallorepressor‐like protein ScaR
Author(s) -
Jakubovics Nicholas S.,
Smith Anthony W.,
Jenkinson Howard F.
Publication year - 2000
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2000.02122.x
Subject(s) - streptococcus gordonii , operon , biology , corynebacterium diphtheriae , diphtheria toxin , repressor , microbiology and biotechnology , permease , promoter , virulence , atp binding cassette transporter , peptide sequence , biochemistry , toxin , gene , streptococcus , gene expression , genetics , bacteria , diphtheria , escherichia coli , transporter , virology , vaccination
The acquisition of transition metal ions by pathogenic bacteria is crucial to their growth and survival within the human host, however, the mechanisms of metal ion homeostasis in streptococci are unknown. The scaCBA operon in the human oral bacterium Streptococcus gordonii encodes the components of an ABC‐type transporter for manganese (Mn 2+ ). Production of substrate‐binding lipoprotein ScaA was increased approximately fivefold in cells cultured in low Mn 2+ medium (< 0.1 µM Mn 2+ ), but not in iron (Fe 2+ /Fe 3+ )‐limited medium, and was enhanced in the presence of human saliva or serum. mRNA analysis revealed that under low Mn 2+ conditions, levels of scaCBA transcript (2.6 kb) were increased > 20‐fold. The Mn 2+ ‐responsive transcriptional regulator of the sca operon was purified and characterized as a 215‐amino‐acid residue polypeptide, designated ScaR, with 26% identity to the Corynebacterium diphtheriae diphtheria toxin repressor (DtxR). Inactivation of scaR in S. gordonii DL1 (Challis) resulted in constitutive derepression of sca operon transcription. Expression of tpx , located immediately downstream of scaA and encoding a putative thiol peroxidase, was not subject to ScaR regulation. Purified ScaR protein bound to the scaC promoter region in vitro in the presence of Mn 2+ ( K d ∼ 80 nM) and, to a lesser extent, in the presence of Ni 2+ or Zn 2+ . The metalloregulator protein binding region was localized by DNA protection analysis to a 46 bp sequence encompassing the −35 and −10 promoter signatures. This sequence was well conserved within the promoters of corresponding virulence‐related permease operons in other streptococci. The results identify a new Mn 2+ ‐sensing regulator of Mn 2+ transport in streptococci, important for Mn 2+ homeostasis during infection of the human host.