Reactive and potentially toxic cofactors such as copper ions are imported into eukaryotic cells and incorporated into target proteins by unknown mechanisms. Atx1, a prototypical copper chaperone protein from yeast, has now been shown to act as a soluble cytoplasmic copper(I) receptor that can adopt either a two- or three-coordinate metal center in the active site. Atx1 also associated directly with the Atx1-like cytosolic domains of Ccc2, a vesicular protein defined in genetic studies as a member of the copper-trafficking pathway. The unusual structure and dynamics of Atx1 suggest a copper exchange function for this protein and related domains in the Menkes and Wilson disease proteins.

No abstract

Fluorescent cell-permeant compounds based on 6-methoxy-8-p-toluenesulfonamido-quinoline, TSQ, are potentially powerful probes of intracellular zinc chemistry; however, the structure, thermodynamics, and stoichiometry of the metal complexes, and the molecular basis of Zn(II) recognition, remain open issues. To address these, we report the first structural characterization of a Zn(II) complex of a TSQ derivative, namely 2-methyl-6-methoxy-8-p-toluenesulfonamido-quinoline (3) and describe its unusual coordination chemistry. The crystal structure of the fluorescent complex of 3 with zinc reveals a 2:1 stoichiometry wherein bidentate coordination of two nitrogens from each ligand gives rise to a highly distorted tetrahedral Zn(II) center. Both sulfonamido groups in the zinc complex are tilted away from zinc to make room for coordination of the amide nitrogens. Zn-O(2) and Zn-O(4) distances are essentially nonbonding (3.06 and 3.10 A, respectively). The bond angles [N(1)-Zn-N(2) 83.5 degrees and N(3)-Zn-N(4) 83.0 degrees] are quite small relative to the 109 degrees angle of an ideal tetrahedral center. This result provides an insight into the zinc-binding mode of the TSQ derivative zinquin, in which a methyl group replaces the hydrogen in the 2-position of the quinoline ring. The methyl group and sulfonamide oxygen atoms clearly hinder formation of both square planar and octahedral complexes. We also show here that the Zn(II) complex of 3 in DMSO-water (80/20 w/w) exhibits an overall binding stability (log beta 2 = 18.24 +/- 0.02) similar to zinquin. Fluorescence microscopy suggests that each of these members of this family demarks a similar set of Zn(II)-enriched compartments that are common to all eukaryotic cells examined to date, and further shows that the ester function is not required for observation of these ubiquitous Zn-loaded compartments. The combined structural, thermodynamic, and physiological results provide a basis for design of other Zn(II)-specific membrane permeant probes with a range of Zn(II) affinities and photophysical properties.

While mercury-199 NMR is a well-established tool for elucidating details of coordination chemistry in biochemical and inorganic complexes, historically the technique has been associated with the use of the extremely toxic chemical, dimethylmercury, as a reference standard. In the twenty-five years since an accidental exposure to dimethylmercury led to the tragic death of Dr.Karen Wetterhahn, the community has learned a great deal about the insidious neurotoxicity of this compound as well as more appropriate ways to avoid exposure. Here, we track the general shift towards the use of alternative mercury reference standards, and away from dimethylmercury.

While mercury-199 NMR is a well-established tool for elucidating details of coordination chemistry in biochemical and inorganic complexes, historically the technique has been associated with the use of the extremely toxic chemical, dimethylmercury, as a reference standard. In the twenty-five years since an accidental exposure to dimethylmercury led to the tragic death of Dr. Karen Wetterhahn, the community has learned a great deal about the insidious neurotoxicity of this compound as well as more appropriate ways to avoid exposure. Here, we track the general shift towards the use of alternative mercury reference standards, and away from dimethylmercury.