4qot
Crystal structure of human copper chaperone bound to the platinum ion
Structural highlights
FunctionATOX1_HUMAN Binds and deliver cytosolic copper to the copper ATPase proteins. May be important in cellular antioxidant defense. Publication Abstract from PubMedCopper trafficking proteins have been implicated in the cellular response to platinum anticancer drugs. We investigated the reaction of the chaperone Atox1 with an activated form of oxaliplatin, the third platinum drug to reach worldwide approval. Unlike cisplatin, which contains monodentate ammines, oxaliplatin contains chelated 1,2-diaminocyclohexane (DACH), which is more resistant to displacement by nucleophiles. In solution, one or two {Pt(DACH)(2+)} moieties bind to the conserved CXXC metal-binding motif of Atox1; in the latter case the two sulfur atoms likely bridging the two platinum units. At longer reaction times, a dimeric species is formed whose composition, Atox12.Pt(2+)2, indicates complete loss of the diamine ligands. Such a dimerization process is accompanied by partial unfolding of the protein. Crystallization experiments aiming at the characterization of the monomeric species have afforded, instead, a dimeric species resembling that already obtained by Boal and Rosenzweig in a similar reaction performed with cisplatin. However, while in the latter case there was only one Pt-binding site (0.4 occupancy) made of four sulfur atoms of the CXXC motifs of the two Atox1 chains in a tetrahedral arrangement, we found, in addition, a secondary Pt-binding site involving Cys41 of the B chain (0.25 occupancy). Moreover, both platinum atoms have lost their diamines. Thus, there appears to be little relationship between what is observed in solution and what is formed in the solid state. Since full occupancy of the tetrahedral cavity is a common feature of all Atox1 dimeric structures obtained with other metal ions (Cu(+), Cd(2+), and Hg(2+)), we propose that in the case of platinum, where the occupancy is only 0.4, the remaining cavities are occupied by Cu(+) ions. Experimental evidence is reported in support of the latter hypothesis. Our proposal represents a meeting point between the initial proposal of Boal and Rosenzweig (0.4 Pt occupancy) and the reinterpretation of the original crystallographic data put forward by Shabalin et al. (1 Cu occupancy), and could apply to other cases. Oxaliplatin Binding to Human Copper Chaperone Atox1 and Protein Dimerization.,Belviso BD, Galliani A, Lasorsa A, Mirabelli V, Caliandro R, Arnesano F, Natile G Inorg Chem. 2016 Jul 5;55(13):6563-73. doi: 10.1021/acs.inorgchem.6b00750. Epub, 2016 Jun 15. PMID:27305454[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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