Characterization and structure of the manganese-responsive transcriptional regulator ScaR.
The streptococcal coaggregation regulator (ScaR) of Streptococcus gordonii is a manganese-dependent transcriptional regulator. When intracellular manganese concentrations become elevated, ScaR represses transcription of the scaCBA operon, which encodes a manganese uptake transporter. A member of the DtxR/MntR family of metalloregulators, ScaR shares sequence similarity with other family members, and many metal-binding residues are conserved. Here, we show that ScaR is an active dimer, with two dimers binding the 46 base pair scaC operator. Each ScaR subunit binds two manganese ions, and the protein is activated by a variety of other metal ions, including Cd(2+), Co(2+), and Ni(2+) but not Zn(2+). The crystal structure of apo-ScaR reveals a tertiary and quaternary structure similar to its homologue, the iron-responsive regulator DtxR. While each DtxR subunit binds a metal ion in two sites, labeled primary and ancillary, crystal structures of ScaR determined in the presence of Cd(2+) and Zn(2+) show only a single occupied metal-binding site that is novel to ScaR. The site analogous to the primary site in DtxR is unoccupied, and the ancillary site is absent from ScaR. Instead, metal ions bind to ScaR at a site labeled "secondary", which is composed of Glu80, Cys123, His125, and Asp160 and lies roughly 5 A away from where the ancillary site would be predicted to exist. This difference suggests that ScaR and its closely related homologues are activated by a mechanism distinct from that of either DtxR or MntR.
Department of Chemistry, Reed College, Portland, Oregon 97202, USA.
Kate E
KE
Stoll
William E
WE
Draper
Joseph I
JI
Kliegman
Misha V
MV
Golynskiy
Rhoda A T
RA
Brew-Appiah
Rebecca K
RK
Phillips
Hattie K
HK
Brown
Wendy A
WA
Breyer
Nicholas S
NS
Jakubovics
Howard F
HF
Jenkinson
Richard G
RG
Brennan
Seth M
SM
Cohen
Arthur
A
Glasfeld
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D002104:Cadmium / Q000494:pharmacology; D002850:Chromatography, Gel; D003035:Cobalt / Q000494:pharmacology; D018360:Crystallography, X-Ray; D004247:DNA / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects / Q000235:genetics; D008345:Manganese / Q000494:pharmacology*; D008969:Molecular Sequence Data; D009532:Nickel / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D055503:Protein Multimerization; D017386:Sequence Homology, Amino Acid; D013291:Streptococcus / Q000378:metabolism*; D014461:Ultracentrifugation; D015032:Zinc / Q000494:pharmacology
D001426:Bacterial Proteins; D002104:Cadmium; D003035:Cobalt; D008345:Manganese; D009532:Nickel; D004247:DNA; D015032:Zinc