Extended Data Fig. 5: NTD is responsible for tetramerization.

a, Electron microscopy map of the tetrameric ACAT1, displayed at low threshold (0.004) in Chimera, reveals extra cytosolic densities that may belong to the NTD. b, Tetrameric ACAT1 shown in the lumenal (left) and cytosolic (right) views. The insets show residues on the tetrameric interface. c, Validation of the oligomeric states of dimeric and monomeric mutants using SEC. SEC profiles and corresponding SDS–PAGE gels for wild-type ACAT1 and two variants, ACAT1(ΔNTD) and ACAT1(ΔNTD-3A), in GDN micelles are shown. The experiment was independently repeated twice with similar results. d, A representative micrograph (left) and representative 2D averages (right) of ACAT1(ΔNTD). The box size for the 2D averages is 220 Å, whereas that for wild-type ACAT1 is 310 Å. e, The two protomers in each dimer are nearly identical. Superimposition of the two protomers in one dimer is shown. f, Lumenal view of the dimeric ACAT. An open cavity is formed by TM1, TM5, TM6 and TM9 from two protomers around the C2 axis, which is indicated by the black oval in the centre. g, The lumenal cavity in the centre of each dimer is highly hydrophobic. The electrostatic surface potential, calculated in PyMOL, is shown in a cut-open side view.