title: Molecular and structural characterization of the PezAT chromosomal toxin-antitoxin system of the human pathogen Streptococcus pneumoniae.
abstract: The chromosomal pezT gene of the Gram-positive pathogen Streptococcus pneumoniae encodes a protein that is homologous to the zeta toxin of the Streptococcus pyogenes plasmid pSM19035-encoded epsilon-zeta toxin-antitoxin system. Overexpression of pezT in Escherichia coli led to severe growth inhibition from which the bacteria recovered approximately 3 h after induction of expression. The toxicity of PezT was counteracted by PezA, which is encoded immediately upstream of pezT and shares weak sequence similarities in the C-terminal region with the epsilon antitoxin. The pezAT genes form a bicistronic operon that is co-transcribed from a sigma(70)-like promoter upstream of pezA and is negatively autoregulated with PezA functioning as a transcriptional repressor and PezT as a co-repressor. Both PezA and the non-toxic PezA(2)PezT(2) protein complex bind to a palindrome sequence that overlaps the promoter. This differs from the epsilon-zeta system in which epsilon functions solely as the antitoxin and transcriptional regulation is carried out by another protein designated omega. Results from site-directed mutagenesis experiments demonstrated that the toxicity of PezT is dependent on a highly conserved phosphoryltransferase active site and an ATP/GTP nucleotide binding site. In the PezA(2)PezT(2) complex, PezA neutralizes the toxicity of PezT by blocking the nucleotide binding site through steric hindrance.
authors.affiliation: Department of Biomolecular Mechanisms, Max-Planck-Institute for Medical Research, 69120 Heidelberg, Germany.
authors.forename: Seok Kooi
authors.initials: SK
authors.lastname: Khoo
authors.forename: Bernhard
authors.initials: B
authors.lastname: Loll
authors.forename: Wai Ting
authors.initials: WT
authors.lastname: Chan
authors.forename: Robert L
authors.initials: RL
authors.lastname: Shoeman
authors.forename: Lena
authors.initials: L
authors.lastname: Ngoo
authors.forename: Chew Chieng
authors.initials: CC
authors.lastname: Yeo
authors.forename: Anton
authors.initials: A
authors.lastname: Meinhart
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D005796:Genes / Q000502:physiology; D016297:Mutagenesis, Site-Directed; D009876:Operon / Q000502:physiology; D011401:Promoter Regions, Genetic / Q000502:physiology; D011485:Protein Binding / Q000235:genetics; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D012097:Repressor Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism; D013296:Streptococcus pneumoniae / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity; D013297:Streptococcus pyogenes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D040681:Structural Homology, Protein; D014158:Transcription, Genetic / Q000502:physiology; D014166:Transferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D012097:Repressor Proteins; D012808:Sigma Factor; D014166:Transferases