Crystal structure of a copper binding domain from HMA7, a P-type ATPase

Experimental Data Snapshot

  • Resolution: 1.70 Å
  • R-Value Free: 0.160 
  • R-Value Work: 0.142 
  • R-Value Observed: 0.142 

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Metal binding affinities of Arabidopsis zinc and copper transporters: selectivities match the relative, but not the absolute, affinities of their amino-terminal domains.

Zimmermann, M.Clarke, O.B.Gulbis, J.M.Keizer, D.W.Jarvis, R.S.Cobbett, C.S.Hinds, M.G.Xiao, Z.Wedd, A.G.

(2009) Biochemistry 48: 11640-11654

  • DOI: https://doi.org/10.1021/bi901573b
  • Primary Citation of Related Structures:  
    2KKH, 3DXS

  • PubMed Abstract: 

    HMA2, HMA4, and HMA7 are three of the eight heavy metal transporting P(1B)-type ATPases in the simple plant Arabidopsis thaliana. The first two transport Zn(2+), and the third transports Cu(+). Each protein contains soluble N-terminal metal-binding domains (MBDs) that are essential for metal transport. While the MBD of HMA7 features a CxxC sequence motif characteristic of Cu(I) binding sites, those of HMA2 and HMA4 contain a CCxxE motif, unique for plant Zn(2+)-ATPases. The three MBDs HMA2n (residues 1-79), HMA4n (residues 1-96), and HMA7n (residues 56-127) and an HMA7/4n chimera were expressed in Escherichia coli. The chimera features the ICCTSE motif from HMA4n inserted in place of the native MTCAAC motif of HMA7n. Binding affinities for Zn(II) and Cu(I) of each MBD were determined by ligand competition with a number of chromophoric probes. The challenges of using these probes reliably were evaluated, and the relative affinities of the MBDs were verified by independent cross-checks. The affinities of HMA2n and HMA4n for Zn(II) are higher than that of HMA7n by a factor of 20-30, but the relative affinities for Cu(I) are inverted by a factor of 30-50. These relativities are consistent with their respective roles in metal selection and transportation. Chimera HMA7/4n binds Cu(I) with an affinity between those of HMA4n and HMA7n but binds Zn(II) more weakly than either parent protein does. The four MBDs bind Cu(I) more strongly than Zn(II) by factors of >10(6). It is apparent that the individual MBDs are not able to overcome the large thermodynamic preference for Cu(+) over Zn(2+). This information highlights the potential toxicity of Cu(+) in vivo and why copper sensor proteins are approximately 6 orders of magnitude more sensitive than zinc sensor proteins. Metal speciation must be controlled by multiple factors, including thermodynamics (affinity), kinetics (including protein-protein interactions), and compartmentalization. The structure of Zn(II)-bound HMA4n defined by NMR confirmed the predicted ferredoxin betaalphabetabetaalphabeta fold. A single Zn atom was modeled onto a metal-binding site with protein ligands comprising the two thiolates and the carboxylate of the CCxxE motif. The observed (113)Cd chemical shift in [(113)Cd]HMA4n was consistent with a Cd(II)S(2)OX (X = O or N) coordination sphere. The Zn(II) form of the Cu(I) transporter HMA7n is a monomer in solution but crystallized as a polymeric chain [(Zn(II)-HMA7n)(m)]. Each Zn(II) ion occupied a distorted tetrahedral site formed from two Cys ligands of the CxxC motif of one HMA7n molecule and the amino N and carbonyl O atoms of the N-terminal methionine of another.

  • Organizational Affiliation

    School of Chemistry, University of Melbourne, Parkville, Victoria 3010, Australia.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Copper-transporting ATPase RAN1A [auth X]74Arabidopsis thalianaMutation(s): 1 
Gene Names: RAN1At5g44790K23L20.14T19K24.18
Find proteins for Q9S7J8 (Arabidopsis thaliana)
Explore Q9S7J8 
Go to UniProtKB:  Q9S7J8
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupQ9S7J8
Sequence Annotations
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Resolution: 1.70 Å
  • R-Value Free: 0.160 
  • R-Value Work: 0.142 
  • R-Value Observed: 0.142 
  • Space Group: P 21 21 21
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 27.374α = 90
b = 44.529β = 90
c = 49.223γ = 90
Software Package:
Software NamePurpose
HKL-2000data collection
HKL-2000data reduction
HKL-2000data scaling

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2009-08-11
    Type: Initial release
  • Version 1.1: 2011-07-13
    Changes: Version format compliance
  • Version 1.2: 2021-11-10
    Changes: Database references, Derived calculations