title: The zinc efflux activator SczA protects Streptococcus pneumoniae serotype 2 D39 from intracellular zinc toxicity.
abstract: Zinc is an essential trace element that serves as a catalytic cofactor in metalloenzymes and a structural element in proteins involved in general metabolism and cellular defenses of pathogenic bacteria. Despite its importance, high zinc levels can impair cellular processes, inhibiting growth of many pathogenic bacteria, including the major respiratory pathogen Streptococcus pneumoniae. Zinc intoxication is prevented in S. pneumoniae by expression of the zinc exporter CzcD, whose expression is activated by the novel TetR-family transcriptional zinc-sensing regulator SczA. How zinc bioavailability triggers activation of SczA is unknown. It is shown here through functional studies in S. pneumoniae that an unannotated homodimeric TetR from S. agalactiae (PDB 3KKC) is the bona fide zinc efflux regulator SczA, and binds two zinc ions per protomer. Mutagenesis analysis reveals two metal binding sites, termed A and B, located on opposite sides of the SczA C-terminal regulatory domain. In vivo, the A- and B-site SczA mutant variants impact S. pneumoniae resistance to zinc toxicity and survival in infected macrophages. A model is proposed for S. pneumoniae SczA function in which both A- and B-sites were required for transcriptional activation of czcD expression, with the A-site serving as the evolutionarily conserved intracellular sensing site in SczAs.
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, IN, 47405-7005, USA.
authors.forename: Julia E
authors.initials: JE
authors.lastname: Martin
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, IN, 47405-7005, USA.
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Edmonds
authors.affiliation: Department of Biology, Indiana University, Bloomington, IN, 47405-7005, USA.
authors.forename: Kevin E
authors.initials: KE
authors.lastname: Bruce
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, IN, 47405-7005, USA.
authors.forename: Gregory C
authors.initials: GC
authors.lastname: Campanello
authors.affiliation: Research Centre for Infectious Diseases, School of Biological Sciences, the University of Adelaide, SA, 5005, Australia.
authors.forename: Bart A
authors.initials: BA
authors.lastname: Eijkelkamp
authors.affiliation: Research Centre for Infectious Diseases, School of Biological Sciences, the University of Adelaide, SA, 5005, Australia.
authors.forename: Erin B
authors.initials: EB
authors.lastname: Brazel
authors.affiliation: Research Centre for Infectious Diseases, School of Biological Sciences, the University of Adelaide, SA, 5005, Australia.
authors.forename: Christopher A
authors.identifier: 0000-0003-1596-4841
authors.initials: CA
authors.lastname: McDevitt
authors.affiliation: Department of Biology, Indiana University, Bloomington, IN, 47405-7005, USA.
authors.forename: Malcolm E
authors.identifier: 0000-0002-1482-2588
authors.initials: ME
authors.lastname: Winkler
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, IN, 47405-7005, USA.
authors.forename: David P
authors.identifier: 0000-0002-2342-1620
authors.initials: DP
authors.lastname: Giedroc
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000378:metabolism; D001682:Biological Availability; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D000075322:Heavy Metal Poisoning; D019216:Metals, Heavy / Q000378:metabolism; D011041:Poisoning / Q000235:genetics / Q000378:metabolism; D013292:Streptococcus agalactiae / Q000378:metabolism; D013296:Streptococcus pneumoniae / Q000378:metabolism; D013753:Tetracycline Resistance; D015032:Zinc / Q000378:metabolism* / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D019216:Metals, Heavy; D015032:Zinc