title: The ligand environment of zinc stored in vesicles.
abstract: Zinc serves regulatory functions in cells and thus, several mechanisms exist for tight control of its homeostasis. One mechanism is storage in and retrieval from vesicles, so-called zincosomes, but the chemical speciation of zincosomal zinc has remained enigmatic. Here, we determine the intravesicular zinc-coordination in isolated zincosomes in comparison to intact RAW264.7 murine macrophage cells. In elemental maps of a cell monolayer, generated by microbeam X-ray fluorescence, zincosomes were identified as spots of high zinc accumulation. A fingerprint for the binding motif obtained by muXANES (X-ray absorption near edge structure) matches the XANES from isolated vesicles; zinc is not free, but present as a complexed form (average coordination; 1.0 sulfur, 2,5 histidines 30 and 1.0 oxygen), resembling regulatory or catalytic zinc sites in proteins. Such coordination enables reversible binding, acting as a 'zinc sink', facilitating the accumulation of high amounts of zinc against a concentration gradient.
authors.affiliation: European Molecular Biology Laboratory, Hamburg Outstation, c/o DESY, Notkestrasse 85, D-22603 Hamburg, Germany.
authors.forename: Gerd
authors.initials: G
authors.lastname: Wellenreuther
authors.forename: Michele
authors.initials: M
authors.lastname: Cianci
authors.forename: Remi
authors.initials: R
authors.lastname: Tucoulou
authors.forename: Wolfram
authors.initials: W
authors.lastname: Meyer-Klaucke
authors.forename: Hajo
authors.initials: H
authors.lastname: Haase
mesh_terms: D000818:Animals; D002460:Cell Line; D022162:Cytoplasmic Vesicles / Q000378:metabolism*; D008024:Ligands; D051379:Mice; D015032:Zinc / Q000378:metabolism*
chemical_list: D008024:Ligands; D015032:Zinc