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. 2020 Nov 23;296:100029. doi: 10.1074/jbc.RA120.014739

Figure 2.

Figure 2

Class averages and 3D maps of FtsH hexamers.A–D, class averages of the negatively stained specimen represent its side or tilted views. The scale bar represents 11 nm. E, schematic representation of the class averages comprising the periplasmic domain (blue), the transmembrane domain composed of 12 transmembrane helices kept in solution by the LMNG-micelle (green), and the cytosolic domain (blue). Dashed blue lines indicate six linking peptides present in the protein sequence. F, 3D maps calculated from images of negatively stained full-length AaFtsH hexamers. G, fitting of the crystal structure of the cytosolic domain of AaFtsH (PDB 4WW0) and the crystal structure of the periplasmic domain of E. coli FtsH (PDB 4V0B) to the hexamer map. H, left to right: cryo-EM class averages of the AaFtsH hexamer showing its side, top, and tilted views. I, left: structure of FtsH hexamer in C6 symmetry at the nominal resolution of 6.6 Å, colored according to local resolution analysis results. I, right: cross section through the structure in the vicinity of the C6 axis, showing two distinct connections of the N-terminal domain to the cytosolic domain (marked by black arrows). One fitted subunit of the FtsH X-ray cytosolic structure 4WW0 is shown in red, with a red arrow pointing at the position of its M141 residue. Pink ribbons indicate the position of the fitted 4V0B structure of the periplasmic domain. J, detailed views at the C6-symmetric N-terminal domain. Left: a top view along the C6 axis at a high threshold shows an inner and outer N-terminal ring; right: isolated N-terminal domain subunit forming a U-turn in the periplasmic domain (arrow). Black star and dot indicate connections to the cytosolic domain. K, left: a side view of the cryo-EM map of the AaFtsH hexamer resolved without a symmetry constraint at 16-Å resolution, displaying a tilted and disordered N-terminal domain. K, right: a cross section through the cryo-EM map. Arrows point at the opening into cytosol. L, positions of three of the YME1 protease subunits fitted into the asymmetric cytosolic chamber of FtsH. ADP-bound (6AZ0.E) is depicted in yellow, apo- (6AZ0.F) in blue, and ATP-bound (6AZ0.A) in red. ADP molecule is depicted as green spheres, ATP as cyan.