title: Copper trafficking in the CsoR regulon of Streptomyces lividans.
abstract: In the actinobacterium Streptomyces lividans copper homeostasis is controlled through the action of the metalloregulator CsoR. Under copper stress, cuprous ions bind to apo-CsoR resulting in the transcriptional derepression of genes encoding for copper efflux systems involving CopZ-like copper chaperones and CopA-like P-type ATPases. Whether CsoR obtains copper via a protein-protein mediated trafficking mechanism is unknown. In this study we have characterised the copper trafficking properties of two S. lividans CopZ proteins (SLI_1317 and SLI_3079) under the transcriptional control of a CsoR (SLI_4375). Our findings indicate that both CopZ-proteins have cysteine residues in the Cu(i) binding MX1CX2X3C motif with acid-base properties that are modulated for a high cuprous ion affinity and favourable Cu(i)-exchange with a target. Using electrophoretic mobility shift assays transfer of Cu(i) is shown to occur in a unidirectional manner from the CopZ to the CsoR. This transfer proceeds via a shallow thermodynamic affinity gradient and is also kinetically favoured through the modulation of the acid-base properties of the cysteine residues in the Cys2His cuprous ion binding motif of CsoR. Using RNA-seq coupled with the mechanistic insights of Cu(i) transfer between CopZ and CsoR in vitro, we propose a copper trafficking pathway for the CsoR regulon that initially involves the buffering of cytosolic copper by three CopZ chaperones followed by transfer of Cu(i) to CsoR to illicit a transcriptional response.
authors.affiliation: School of Biological Science, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK. jworrall@essex.ac.uk.
authors.forename: Amanda K
authors.initials: AK
authors.lastname: Chaplin
authors.forename: Benedict G
authors.initials: BG
authors.lastname: Tan
authors.forename: Erik
authors.initials: E
authors.lastname: Vijgenboom
authors.forename: Jonathan A R
authors.initials: JA
authors.lastname: Worrall
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003300:Copper / Q000378:metabolism*; D003545:Cysteine; D005798:Genes, Bacterial / Q000235:genetics; D056511:Metallochaperones / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D018085:Regulon / Q000235:genetics; D016415:Sequence Alignment; D048170:Streptomyces lividans / Q000235:genetics* / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D056511:Metallochaperones; D003300:Copper; D003545:Cysteine