Extended Data Figure 2 |. Image processing for the cryo-EM data of nucleotide-free LptB₂FG in nanodiscs.

a, Representative cryo-EM image of nucleotide-free LptB₂FG in nanodiscs. b, 2D class averages of cryo-EM particle images. c, 3D classification and refinement of cryo-EM particle images. After the first round of 3D classification, all particles classified into the two best classes (#3 and #6) in the final 5 iterations (indicated as “5 cycles”) were kept for further processing. 3D classification focusing on the TMD was used to obtain the final cryo-EM map. LPS density is indicated with a green circle. EM data collection and 2D classification were performed once.