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

FIGURE 5.

FIGURE 5

Accessory subunits NDUFA5 and NDUFA7. (A) The structure of CI (PDB: 6ZKC) in cartoon with the surface of NDUFA5 (auburn) shown, the core subunits colored as in Figure 1A and the accessory subunits grey. (B–D) The NDUFA5 C-terminus compensates for a shorter NDUFS3 (corn yellow) β3-4S3 loop. (B) Mammalian (PDB: 6ZKC), (C) T. thermophilus (PDB: 4HEA) and (D) E. coli (PDB: 7NZ1). CI structures shown in transparent surface with NDUFA5 and the NDUFS3 β3-4S3 loop in cartoon. (E–G) NDUFA5 may compensate for a shorter NDUFS3 β4-5S3 loop. (E) O. aries cartoon of NDUFS3 β4-5S3 loop (aa 99–102), NDUFA5, and NDUFS8 (sea green) on the CI surface (PDB: 6ZKC). The β4-5S3 loop is shorter in O. aries than in bacteria. (F) T. thermophilus cartoon of the β4-5S3 loop (aa 76–86) and NDUFS8 (Nqo9) on the CI surface (PDB: 4HEA). (G) Y. lipolytica cartoon of the NDUFS3 β4-5S3 (NUGM) loop (aa 147–150), NDUFA5 (NUFM) and NDUFS8 (NUPM) on the CI surface (PDB: 6YJ4). Y. lipolytica has an extended NDUFS8 coil compared to O. aries and T. thermophilus. (H) The structure of CI (PDB: 6ZKC) shown in cartoon with the surface of NDUFA7 (azzure blue), the core subunits colored as in Figure 1 and the accessory subunits grey. (I–K) Differences in NDUFA7 between eukaryotes. (I) O. aries NDUFA7 shown as cartoon on the CI (PDB: 6ZKC) surface with the variable region indicated (*) and the N-terminal coil and helix of NDUFS3 shown as cartoon. A: ascending coil, L: lateral coil, D: descending coil. (J) Y. lipolytica NDUFA7 (NUZM) shown as cartoon on the CI (PDB: 4HEA) surface with the variable region indicated (*) and the N-terminal coil and helix and C-terminal coil of NDUFS3 (NUGM) shown as cartoon. (K) V. radiata NDUFA7 (NDUA7) shown as cartoon on the CI (PDB: 6X89) surface with the variable region indicated (*) and the N-terminal coil and helix of NDUFS3 (NDUS3) shown as cartoon. (L) A conformation change is needed in the N-terminal helix of NDUFS3 relative to that from T. thermophilus to accommodate NDUFA7. Cartoon of NDUFS3 in O. aries (PDB: 6ZKC) and NDUFS3 (Nqo5; grey) in T. thermophilus (PDB: 4HEA) on the O. aries CI surface. (M,N) NDUFA7 participates in NDUFA12 (gold) binding. (M) Cartoon of NDUFA7 (NUZM), the N-terminal and C-terminal loop of NDUFS3 (NUGM) and NDUFA12 (N7BM) on the CI surface (PDB: 6YJ4). (N) Cartoon of NDUFA7, NDUFS3 and NDUFAF2 (N7BML) (gold) on the CI surface (PDB: 6RFQ). The N-terminal regions of NDUFA7 and NDUFS3 are disordered. (O–Q) Stabilizing role for NDUFA7 at the interface of the N and Q modules. (O) O. aries cartoon of NDUFA7 on CI surface (PDB:6ZKC). NDUFA7 stabilizing interactions are replaced by core subunits in bacteria. A: ascending coil, L: lateral coil. (P) T. thermophilus cartoon of NDUFS1 (orange) (Nqo1) on CI surface (PDB: 4HEA). (Q) E. coli cartoon of C-terminal coil of NDUFV1 (NuoF) on CI surface (PDB: 7NZ1). Subunits are colored as in Figure 1 throughout unless stated otherwise. NDUFA5: auburn, NDUFS3: corn yellow, NDUFS8: sea green, NDUFA7: azzure blue, NDUFA12: gold, NDUFS1: orange.