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. 2022 Jan 3;8:798353. doi: 10.3389/fmolb.2021.798353

FIGURE 6.

FIGURE 6

Accessory subunits NDUFA6, NDUFAB1-α, NDUFB9, and NDUFAB1-β in mammalian CI. (A) The structure of CI in cartoon with the surfaces of NDUFA6 (cinnabar red)/NDUFAB1-α (violet) and NDUFB9 (yellow orange)/NDUFAB1-β (violet) shown, the core subunits colored as in Figure 1A and the accessory subunits grey. (B) Shin view CI showing the NDUFA6/NDUFAB1-β pair in cartoon and other CI subunits as transparent surfaces. The acylated 4′-phosphopantetheine group is shown in spheres (PDB: 5LNK). (C) Looking down on the toe of CI (PDB: 6ZKC) showing the NDUFB9/NDUFAB1-β pair in cartoon and the other CI subunits as transparent surfaces. (D–F) NDUFA6 replaces structural elements of bacterial CI. Shin view of (D) mammalian (PDB: 5LNK), (E) E. coli (PDB: 7NYR) and (F) T. thermophilus CI shown as transparent surface with NDUFA6, the NDUFS2/S3 (NuoCD) (corn yellow) linker and NDUFS3 C-termini shown in cartoon. Accessory subunits that are not important for the discussion are omitted from panel (D) for clarity. The NDUFS2/S3 (NuoCD) linker in E. coli and Nqo16 (pink) subunit in T. thermophilus conflict with the position of NDUFA6 in mammals. NDUFA6: cinnabar red, NDUFAB1-α: violet, NDUFB9: yellow orange, NDUFAB1-β: violet/violet, NDUFS2/S3: corn yellow, Nqo16: pink.