Complexes biscyclopentadienyles avec des liaisons metal de transitionmercure

Solution structure of the Cu(I) and apo forms of the yeast metallochaperone, Atx1

The (1)H NMR solution structure of the Cu(I)-bound form of Atx1, a 73-amino acid metallochaperone protein from the yeast Saccharomyces cerevisiae, has been determined. Ninety percent of the (1)H and 95% of the (15)N resonances were assigned, and 1184 meaningful NOEs and 42 (3)J(HNH)(alpha) and 60 (1)J(HN) residual dipolar couplings provided a family of structures with rmsd values to the mean structure of 0.37 +/- 0.07 A for the backbone and 0.83 +/- 0.08 A for all heavy atoms. The structure is constituted by four antiparallel beta strands and two alpha helices in a betaalphabetabetaalphabeta fold. Following EXAFS data [Pufahl, R., Singer, C. P., Peariso, K. L., Lin, S.-J., Schmidt, P. J., Fahrni, C. J., Cizewski Culotta, V., Penner-Hahn, J. E., and O'Halloran, T. V. (1997) Science 278, 853-856], a copper ion can be placed between two sulfur atoms of Cys15 and Cys18. The structure of the reduced apo form has also been determined with similar resolution using 1252 meaningful NOEs (rmsd values for the family to the mean structure are 0.67 +/- 0.12 A for the backbone and 1.00 +/- 0.12 A for all heavy atoms). Comparison of the Cu(I) and apo conformations of the protein reveals that the Cu(I) binding cysteines move from a buried site in the bound metal form to a solvent-exposed conformation on the surface of the protein after copper release. Furthermore, copper release leads to a less helical character in the metal binding site. Comparison with the Hg(II)-Atx1 solid-state structure [Rosenzweig, A. C., Huffman, D. L., Hou, M. Y., Wernimont, A. K., Pufahl, R. A., and O'Halloran, T. V. (1999) Structure 7, 605-617] provides insights into the copper transfer mechanism, and a pivotal role for Lys65 in the metal capture and release process is proposed.

Structures of the reduced and mercury-bound forms of MerP, the periplasmic protein from the bacterial mercury detoxification system

Bacteria carrying plasmids with the mer operon, which encodes the proteins responsible for the bacterial mercury detoxification system, have the ability to transport Hg(II) across the cell membrane into the cytoplasm where it is reduced to Hg(0). This is significant because metallic mercury is relatively nontoxic and volatile and thus can be passively eliminated. The structures of the reduced and mercury-bound forms of merP, the periplasmic protein, which binds Hg(II) and transfers it to the membrane transport protein merT, have been determined in aqueous solution by multidimensional NMR spectroscopy. The 72-residue merP protein has a betaalpha betabeta alphabeta fold with the two alpha helices overlaying a four-strand antiparallel beta sheet. Structural differences between the reduced and mercury-bound forms of merP are localized to the metal binding loop containing the consensus sequence GMTCXXC. The structure of the mercury-bound form of merP shows that Hg(II) is bicoordinate with the Cys side chain ligands, and this is confirmed by the chemical shift frequency of the 199Hg resonance.

Mercury-199 NMR of the metal receptor site in MerR and its protein-DNA complex

Structural insights have been provided by mercury-199 nuclear magnetic resonance (NMR) into the metal receptor site of the MerR metalloregulatory protein alone and in a complex with the regulatory target, DNA. The one- and two-dimensional NMR data are consistent with a trigonal planar Hg-thiolate coordination environment consisting only of Cys side chains and resolve structural aspects of both metal ion recognition and the allosteric mechanism. These studies establish 199Hg NMR techniques as useful probes of the metal coordination environment of regulatory proteins, copper enzymes, and zinc transcription factor complexes as large as 50 kilodaltons.