title: Cu(I)- and proton-binding properties of the first N-terminal soluble domain of Bacillus subtilis CopA.
abstract: CopA, a P-type ATPase transporter involved in copper detoxification in Bacillus subtilis, contains two soluble Atx1-like domains separated by a short linker at its N-terminus, an arrangement that occurs widely in copper transporters from both prokaryotes and eukaryotes. Both domains were previously found to bind Cu(I) with very high affinity. Above a level of 1 Cu(I) per CopAab, dimerization occurred, leading to a highly luminescent multinuclear Cu(I) species [Singleton C & Le Brun NE (2009) Dalton Trans, 688-696]. To try to understand the contributions of each domain to the complex Cu(I)-binding behaviour of this and related proteins, we purified a wild-type form of the first domain (CopAa). In isolation, the domain bound Cu(I) with very high affinity (K = ∼ 1 × 10(18) m(-1) ) and underwent Cu(I)-mediated protein association, resulting in a mixture of dimer and tetramer species. Addition of further Cu(I) up to 1 Cu(I) per CopAa monomer led to a weakly luminescent species, whereas further additions [2 Cu(I) per CopAa monomer] resulted in protein unfolding. Analysis of the MTCAAC binding motif Cys residue acid-base properties revealed pK(a) values of 5.7 and 7.3, consistent with the pH dependence of Cu(I) binding, and with the proposal that low proton affinity is associated with high Cu(I) affinity. Finally, Cu(I) exchange between CopAa and the chelator bathocuproine sulfonate revealed rapid exchange in both directions, demonstrating an interaction between the protein and the chelator that catalyses metal ion transfer. Overall, CopAa exhibits similarities to CopAab in terms of affinity and complexity of Cu(I) binding, but the details of Cu(I) binding are distinct.
authors.affiliation: Centre for Molecular and Structural Biochemistry, School of Chemistry, University of East Anglia, Norwich, UK.
authors.forename: Liang
authors.initials: L
authors.lastname: Zhou
authors.forename: Chloe
authors.initials: C
authors.lastname: Singleton
authors.forename: Oliver
authors.initials: O
authors.lastname: Hecht
authors.forename: Geoffrey R
authors.initials: GR
authors.lastname: Moore
authors.forename: Nick E
authors.initials: NE
authors.lastname: Le Brun
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000465:Algorithms; D020816:Amino Acid Motifs; D001412:Bacillus subtilis; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D027682:Cation Transport Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002614:Chelating Agents / Q000378:metabolism; D003300:Copper / Q000378:metabolism*; D000073840:Copper-Transporting ATPases; D003545:Cysteine / Q000737:chemistry; D019281:Dimerization; D004795:Enzyme Stability; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010084:Oxidation-Reduction; D010446:Peptide Fragments / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D058767:Protein Unfolding; D011522:Protons; D011994:Recombinant Proteins / Q000378:metabolism; D012995:Solubility
chemical_list: D001426:Bacterial Proteins; D027682:Cation Transport Proteins; D002614:Chelating Agents; D010446:Peptide Fragments; D011522:Protons; D011994:Recombinant Proteins; D003300:Copper; D000251:Adenosine Triphosphatases; D000073840:Copper-Transporting ATPases; D003545:Cysteine