Fig. 1: Cryo-EM structure of apo-closed ABCG2.
From: ABCG2 transports anticancer drugs via a closed-to-open switch
a Final cryo-EM map of nanodisc reconstituted ABCG2 in the absence of added ligands. Nanodisc density is shown in white, and TM5 is colored green. In the apo-closed conformation the TM helices are closed, while the NBDs remain open in a nucleotide-free state. b Overall arrangement of the TM helices in the apo-closed conformation. TM2 is colored magenta, with the central portion that unravels colored cyan. TM5 is colored green. c View from the extracellular space of the TM helix arrangement in the apo-closed conformation. In the apo-closed conformation, Phe439 (cyan sticks) is flipped outward away from the center of the transporter, and rotation of TM5 causes Phe545 (orange sticks) to point towards the opposite ABCG2 monomer, and brings several sulfur containing sidechains (blue and yellow sticks) to the central dimer axis. d View from the extracellular space of the TM helix arrangement in previously determined inward facing ABCG2 cryo-EM structures. TM helices and residues are colored the same as in (c). Red arrows indicate the direction of TM5 rotation in going from inward facing to apo-closed states.
