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Abstract:
The mitochondrial inner membrane ABC transporter Atm1 exports an unknown substrate to the cytosol for
iron-sulfur protein biogenesis, cellular iron regulation, and tRNA thio-modification. Mutations in the human relative
ABCB7 cause the iron storage disease XLSA/A. We determined 3D structures of two complementary states of Atm1 in
lipid nanodiscs by electron cryo-microscopy at 2.9- to 3.4-Å resolution. The inward-open structure resembled the
known crystal structure of nucleotide-free apo-Atm1 closely. The occluded conformation with bound AMP-PNPMg2+
showed a tight association of the two nucleotide-binding domains, a rearrangement of the C-terminal helices,
and closure of the putative substrate-binding cavity in the homodimeric transporter. We identified a hydrophobic
patch on the C-terminal helices of yeast Atm1, which is unique among type IV ABC transporters of known structure.
Truncation mutants of yeast Atm1 suggest that the C-terminal helices stabilize the dimer, yet are not necessary for
closure of the nucleotide-binding domains.
