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Crystal Structures of Nucleotide-Free and Glutathione-Bound Mitochondrial ABC Transporter Atm1

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Science  07 Mar 2014:
Vol. 343, Issue 6175, pp. 1137-1140
DOI: 10.1126/science.1246729

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Crossing the Membrane

Adenosine triphosphate (ATP)–binding cassette (ABC) transporters couple ATP hydrolysis to the translocation of a wide variety of substrates across cell membranes. Srinivasan et al. (p. 1137) describe the structure of a yeast mitochondrial transporter involved in Fe-S protein biogenesis. The structure reveals bound glutathione, which suggests that glutathione is part of the translocated substrate. J. Y. Lee et al. (p. 1133) describe the structure of a bacterial ABC transporter that confers protection against silver and mercury. This protein also binds glutathione derivatives. The structure provides insight into how ligand interactions are coupled to ATP hydrolysis.

Abstract

The yeast mitochondrial ABC transporter Atm1, in concert with glutathione, functions in the export of a substrate required for cytosolic-nuclear iron-sulfur protein biogenesis and cellular iron regulation. Defects in the human ortholog ABCB7 cause the sideroblastic anemia XLSA/A. Here, we report the crystal structures of free and glutathione-bound Atm1 in inward-facing, open conformations at 3.06- and 3.38-angstrom resolution, respectively. The glutathione binding site includes a residue mutated in XLSA/A and is located close to the inner membrane surface in a large cavity. The two nucleotide-free adenosine 5′-triphosphate binding domains do not interact yet are kept in close vicinity through tight interaction of the two C-terminal α-helices of the Atm1 dimer. The resulting protein stabilization may be a common structural feature of all ABC exporters.

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