title: Affinity gradients drive copper to cellular destinations.
abstract: Copper is an essential trace element for eukaryotes and most prokaryotes. However, intracellular free copper must be strictly limited because of its toxic side effects. Complex systems for copper trafficking evolved to satisfy cellular requirements while minimizing toxicity. The factors driving the copper transfer between protein partners along cellular copper routes are, however, not fully rationalized. Until now, inconsistent, scattered and incomparable data on the copper-binding affinities of copper proteins have been reported. Here we determine, through a unified electrospray ionization mass spectrometry (ESI-MS)-based strategy, in an environment that mimics the cellular redox milieu, the apparent Cu(I)-binding affinities for a representative set of intracellular copper proteins involved in enzymatic redox catalysis, in copper trafficking to and within various cellular compartments, and in copper storage. The resulting thermodynamic data show that copper is drawn to the enzymes that require it by passing from one copper protein site to another, exploiting gradients of increasing copper-binding affinity. This result complements the finding that fast copper-transfer pathways require metal-mediated protein-protein interactions and therefore protein-protein specific recognition. Together with Cu,Zn-SOD1, metallothioneins have the highest affinity for copper(I), and may play special roles in the regulation of cellular copper distribution; however, for kinetic reasons they cannot demetallate copper enzymes. Our study provides the thermodynamic basis for the kinetic processes that lead to the distribution of cellular copper.
authors.affiliation: Magnetic Resonance Center CERM and Department of Chemistry, University of Florence, Via Luigi Sacconi 6, 50019, Sesto Fiorentino, Florence, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Banci
authors.forename: Ivano
authors.initials: I
authors.lastname: Bertini
authors.forename: Simone
authors.initials: S
authors.lastname: Ciofi-Baffoni
authors.forename: Tatiana
authors.initials: T
authors.lastname: Kozyreva
authors.forename: Kairit
authors.initials: K
authors.lastname: Zovo
authors.forename: Peep
authors.initials: P
authors.lastname: Palumaa
mesh_terms: D000818:Animals; D055162:Biocatalysis; D002352:Carrier Proteins / Q000378:metabolism*; D002414:Cations, Monovalent / Q000378:metabolism; D003300:Copper / Q000302:isolation & purification / Q000378:metabolism*; D051546:Cyclooxygenase 2 / Q000737:chemistry / Q000378:metabolism; D004229:Dithiothreitol / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism*; D017136:Ion Transport; D007700:Kinetics; D008024:Ligands; D008668:Metallothionein / Q000378:metabolism; D008930:Mitochondria, Liver; D010084:Oxidation-Reduction; D011485:Protein Binding; D051381:Rats; D021241:Spectrometry, Mass, Electrospray Ionization; D013816:Thermodynamics
chemical_list: D002352:Carrier Proteins; D002414:Cations, Monovalent; D008024:Ligands; D003300:Copper; D008668:Metallothionein; D051546:Cyclooxygenase 2; D005978:Glutathione; D004229:Dithiothreitol
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