title: Cytosolic Ni(II) sensor in cyanobacterium: nickel detection follows nickel affinity across four families of metal sensors.
abstract: Efflux of surplus Ni(II) across the outer and inner membranes of Synechocystis PCC 6803 is mediated by the Nrs system under the control of a sensor of periplasmic Ni(II), NrsS. Here, we show that the product of ORF sll0176, which encodes a CsoR/RcnR-like protein now designated InrS (for internal nickel-responsive sensor), represses nrsD (NrsD is deduced to efflux Ni(II) across the inner membrane) from a cryptic promoter between the final two ORFs in the nrs operon. Transcripts initiated from the newly identified nrsD promoter accumulate in response to nickel or cobalt but not copper, and recombinant InrS forms specific, Ni(II)-inhibited complexes with the nrsD promoter region. Metal-dependent difference spectra of Ni(II)- and Cu(I)-InrS are similar to Cu(I)-sensing CsoR and dissimilar to Ni(II)/Co(II)-sensing RcnR, consistent with factors beyond the primary coordination sphere switching metal selectivity. Competition with chelators mag-fura-2, nitrilotriacetic acid, EDTA, and EGTA estimate K(D) Ni(II) for the tightest site of InrS as 2.05 (±1.5) × 10(-14) m, and weaker K(D) Ni(II) for the cells' metal sensors of other types: Zn(II) co-repressor Zur, Co(II) activator CoaR, and Zn(II) derepressor ZiaR. Ni(II) transfer to InrS occurs upon addition to Ni(II) forms of each other sensor. InrS binds Ni(II) sufficiently tightly to derepress Ni(II) export at concentrations below K(D) Ni(II) of the other sensors.
authors.affiliation: Biophysical Sciences Institute, Department of Chemistry, School of Biological and Biomedical Sciences, University of Durham, Durham DH1 3LE, United Kingdom.
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Foster
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Patterson
authors.forename: Rafael
authors.initials: R
authors.lastname: Pernil
authors.forename: Corinna R
authors.initials: CR
authors.lastname: Hess
authors.forename: Nigel J
authors.initials: NJ
authors.lastname: Robinson
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D001667:Binding, Competitive; D002614:Chelating Agents / Q000737:chemistry; D003035:Cobalt / Q000737:chemistry; D016384:Consensus Sequence; D056831:Coordination Complexes / Q000737:chemistry; D003300:Copper / Q000737:chemistry; D003600:Cytosol / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008667:Metalloproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D009532:Nickel / Q000737:chemistry*; D009875:Operator Regions, Genetic; D009876:Operon; D010641:Phenotype; D011485:Protein Binding; D017422:Sequence Analysis, DNA; D013056:Spectrophotometry, Ultraviolet; D046939:Synechocystis; D024363:Transcription Initiation Site; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D002614:Chelating Agents; D056831:Coordination Complexes; D008667:Metalloproteins; D003035:Cobalt; D003300:Copper; D009532:Nickel