title: Threonine phosphorylation prevents promoter DNA binding of the Group B Streptococcus response regulator CovR.
abstract: All living organisms communicate with the external environment for their survival and existence. In prokaryotes, communication is achieved by two-component systems (TCS) comprising histidine kinases and response regulators. In eukaryotes, signalling is accomplished by serine/threonine and tyrosine kinases. Although TCS and serine/threonine kinases coexist in prokaryotes, direct cross-talk between these families was first described in Group B Streptococcus (GBS). A serine/threonine kinase (Stk1) and a TCS (CovR/CovS) co-regulate toxin expression in GBS. Typically, promoter binding of regulators like CovR is controlled by phosphorylation of the conserved active site aspartate (D53). In this study, we show that Stk1 phosphorylates CovR at threonine 65. The functional consequence of threonine phosphorylation of CovR in GBS was evaluated using phosphomimetic and silencing substitutions. GBS encoding the phosphomimetic T65E allele are deficient for CovR regulation unlike strains encoding the non-phosphorylated T65A allele. Further, compared with wild-type or T65A CovR, the T65E CovR is unable to bind promoter DNA and is decreased for phosphorylation at D53, similar to Stk1-phosphorylated CovR. Collectively, we provide evidence for a novel mechanism of response regulator control that enables GBS (and possibly other prokaryotes) to fine-tune gene expression for environmental adaptation.
authors.affiliation: Department of Pediatric Infectious Diseases, University of Washington School of Medicine and Seattle Children's Hospital Research Institute, Seattle, WA 98101, USA.
authors.forename: Wan-Jung
authors.initials: WJ
authors.lastname: Lin
authors.forename: Don
authors.initials: D
authors.lastname: Walthers
authors.forename: James E
authors.initials: JE
authors.lastname: Connelly
authors.forename: Kellie
authors.initials: K
authors.lastname: Burnside
authors.forename: Kelsea A
authors.initials: KA
authors.lastname: Jewell
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Kenney
authors.forename: Lakshmi
authors.initials: L
authors.lastname: Rajagopal
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012329:RNA, Bacterial / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D013292:Streptococcus agalactiae / Q000235:genetics* / Q000378:metabolism; D013912:Threonine / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D012329:RNA, Bacterial; D012097:Repressor Proteins; D013912:Threonine; C474028:Stk1 protein, Streptococcus agalactiae; D017346:Protein Serine-Threonine Kinases