A new zinc-protein coordination site in intracellular metal trafficking: solution structure of the Apo and Zn(II) forms of ZntA(46-118).
Zinc, a metal ion that functions in a wide variety of catalytic and structural sites in metalloproteins, is shown here to adopt a novel coordination environment in the Escherichia coli transport protein ZntA. The ZntA protein is a P-type ATPase that pumps zinc out of the cytoplasm and into the periplasm. It is physiologically selective for Zn(II) and functions with metalloregulatory proteins in the cell to keep the zinc quota within strict limits. Yet, the N-terminal cytoplasmic domain contains a region that is highly homologous to the yeast Cu(I) metallochaperone Atx1. To investigate how the structure of this region may influence its function, this fragment, containing residues 46-118, has been cloned out of the gene and overexpressed. We report here the solution structure of this fragment as determined by NMR. Both the apo and Zn(II)-ZntA(46-118) structures have been determined. It contains a previously unknown protein coordination site for zinc that includes two cysteine residues, Cys59 and Cys62, and a carboxylate residue, Asp58. The solvent accessibility of this site is also remarkably high, a feature that increasingly appears to be a characteristic of domains of heavy metal ion transport proteins. The participation of Asp58 in this ZntA metal ion binding site may play an important role in modulating the relative affinities and metal exchange rates for Zn(II)/Pb(II)/Cd(II) as compared with other P-type ATPases, which are selective for Cu(I) or Ag(I).
Banci
Lucia
L
Magnetic Resonance Center CERM and Department of Chemistry, University of Florence, Via Luigi Sacconi 6, 50019, Sesto Fiorentino, Italy.
Bertini
Ivano
I
Ciofi-Baffoni
Simone
S
Finney
Lydia A
LA
Outten
Caryn E
CE
O'Halloran
Thomas V
TV
D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D001059:Apoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D012996:Solutions; D015032:Zinc / Q000737:chemistry* / Q000378:metabolism
D001059:Apoproteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D012996:Solutions; D000251:Adenosine Triphosphatases; C109898:Zn(II)-translocating P-type ATPase; D015032:Zinc