Fig. 2: Structure of the hydrophilic subunits SdhA and SdhB.
From: Structural basis of menaquinone reduction by succinate dehydrogenase from Chloroflexus aurantiacus
a Overall structure of SdhA, which includes an N-terminal extension of two α-helices (N-helix), a FAD-binding domain (beige), a capping domain (golden yellow), a helical domain (light pink), and a C-terminal domain (orange). FAD is shown in blue stick form. b Succinate and FAD binding pocket. Key residues coordinating succinate (orange) and FAD (blue) are labeled and shown in stick form, with hydrogen bonding interactions indicated by dashed lines. c Conformational changes in the succinate-binding site between the apo-form (white), lipid-bound (gray), and MK-bound (wheat) forms. Loop regions (F167GGA170 and S304E305S306) are shown in cartoon form, with coordinating residues Glu-A305 and Ser-A306 shown in stick form. d Superposition of SdhA (wheat) with those from E. coli (PDB code 1NEK, light pink), Homo sapiens (PDB 8GS8, white), Sus scrofa (PDB 1ZOY, gray) SQRs, M. smegmatis Sdh2 (PDB 6LUM, light blue), and D. gigas (PDB 5XMJ, light green) QFR. The superimposed SdhA structures are displayed as surface. N-helix regions are highlighted in cartoon form. e Spatial organization of the SdhA N-helix in the CaSDH trimer (left) and its interaction with adjacent monomers (right). Zoom in view shows interacting residues (stick) and hydrogen bonding interactions (dashed). f Overall structure of SdhB (left) and coordination of iron-sulfur clusters (right). Iron-sulfur clusters are shown as orange-brown spheres, and coordinating cysteine residues are shown in stick form. Edge-to-edge distances are indicated with orange dashed lines.
