PcoE--a metal sponge expressed to the periplasm of copper resistance Escherichia coli. Implication of its function role in copper resistance.
Expression of the periplasmic protein PcoE of Escherichia coli is induced strongly by cupric salts under the control of the chromosomal copper tolerance system cusRS. Its isolation and study were complicated by de-amidation of Asn 54 and 103 at alkaline pH. Its apo form is essentially unstructured in solution and can be likened to a large unstructured multidentate ligand carrying multiple metal binding sites (15 Met; 10 His; 13 Asp, Glu; 10 Asn; 6 Lys). As expected, it binds multiple soft metal ions Cu(+) and Ag(+) non-cooperatively with the highest affinity for Cu(I) in the picomolar range (K(D)~10(-12) M). Binding of multiple soft ions induced dimerization and formation of some α-helical structure. PcoE also binds the harder metal ions Cu(2+) or Zn(2+) but with lower affinities and in smaller numbers. Cu(II) bound in PcoE is reduced readily to more tightly bound Cu(I). Overall, these properties mean that it is difficult to characterize individual species of defined metal content. Similar properties and difficulties have been reported for the homologous silver-binding protein SilE from Salmonella. However, the properties are consistent with a role for PcoE as a 'metal sponge' acting as a first line of defence against metal toxicity (under the control of the copper tolerance system cusRS) until the copper resistance operon pcoABCD is expressed.
School of Chemistry, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria 3010, Australia.
Matthias
M
Zimmermann
Saumya R
SR
Udagedara
Chak Ming
CM
Sze
Timothy M
TM
Ryan
Geoffrey J
GJ
Howlett
Zhiguang
Z
Xiao
Anthony G
AG
Wedd
D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism; D002413:Cations, Divalent / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D003300:Copper / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000737:chemistry / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D033903:Periplasmic Proteins / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D015032:Zinc / Q000737:chemistry / Q000378:metabolism
D001426:Bacterial Proteins; D002352:Carrier Proteins; D002413:Cations, Divalent; D029968:Escherichia coli Proteins; C462542:PcoE protein, E coli; D033903:Periplasmic Proteins; C117203:SilE protein, Salmonella typhimurium; D003300:Copper; D015032:Zinc