title: Imaging of the intracellular topography of copper with a fluorescent sensor and by synchrotron x-ray fluorescence microscopy.
abstract: Copper is an essential micronutrient that plays a central role for a broad range of biological processes. Although there is compelling evidence that the intracellular milieu does not contain any free copper ions, the rapid kinetics of copper uptake and release suggests the presence of a labile intracellular copper pool. To elucidate the subcellular localization of this pool, we have synthesized and characterized a membrane-permeable, copper-selective fluorescent sensor (CTAP-1). Upon addition of Cu(I), the sensor exhibits a 4.6-fold emission enhancement and reaches a quantum yield of 14%. The sensor exhibits excellent selectivity toward Cu(I), and its emission response is not compromised by the presence of millimolar concentrations of Ca(II) or Mg(II) ions. Variable temperature dynamic NMR studies revealed a rapid Cu(I) self-exchange equilibrium with a low activation barrier of deltaG++ = 44 kJ.mol(-1) and k(obs) approximately 10(5) s(-1) at room temperature. Mouse fibroblast cells (3T3) incubated with the sensor produced a copper-dependent perinuclear staining pattern, which colocalizes with the subcellular locations of mitochondria and the Golgi apparatus. To evaluate and confirm the sensor's copper-selectivity, we determined the subcellular topography of copper by synchrotron-based x-ray fluorescence microscopy. Furthermore, microprobe x-ray absorption measurements at various subcellular locations showed a near-edge feature that is characteristic for low-coordinate monovalent copper but does not resemble the published spectra for metallothionein or glutathione. The presented data provide a coherent picture with strong evidence for a kinetically labile copper pool, which is predominantly localized in the mitochondria and the Golgi apparatus.
authors.affiliation: School of Chemistry and Biochemistry, Georgia Institute of Technology, 770 State Street, Atlanta, GA 30332, USA.
authors.forename: Liuchun
authors.initials: L
authors.lastname: Yang
authors.forename: Reagan
authors.initials: R
authors.lastname: McRae
authors.forename: Maged M
authors.initials: MM
authors.lastname: Henary
authors.forename: Raxit
authors.initials: R
authors.lastname: Patel
authors.forename: Barry
authors.initials: B
authors.lastname: Lai
authors.forename: Stefan
authors.initials: S
authors.lastname: Vogt
authors.forename: Christoph J
authors.initials: CJ
authors.lastname: Fahrni
mesh_terms: D000818:Animals; D003300:Copper / Q000737:chemistry* / Q000493:pharmacokinetics; D005456:Fluorescent Dyes; D006056:Golgi Apparatus / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D051379:Mice; D008856:Microscopy, Fluorescence / Q000379:methods; D008928:Mitochondria / Q000378:metabolism; D008956:Models, Chemical; D041681:NIH 3T3 Cells; D017356:Synchrotrons; D014965:X-Rays
chemical_list: D005456:Fluorescent Dyes; D003300:Copper