Fig. 5: The “distal” quinone binding site (QD) in CaSDH.
From: Structural basis of menaquinone reduction by succinate dehydrogenase from Chloroflexus aurantiacus
a Enlarged view of the QD site with a bound menaquinone-7 (MK7) fitted in clear EM densities. The hemes (red), the MK7 molecule (green), and surrounding residues are shown in stick form, and hydrogen bonding interactions with Glu-C64 are indicated with dashed lines. The QD site (blue) is shown in cartoon form but as surface in the inset. b Structural superposition of the QD site in the apo-form (white) and MK4-bound (blue) structures. The PE molecule (cyan) in the apo-form, the MK4 (dark green), and surrounding amino acid residues are shown in stick form. The QD site is shown in cartoon form but shown as surface in the inset. c Superposition of CaSDH SdhC (slate blue) with E. coli QFR (PDB 1L0V, yellow), revealing overlap of heme bD with MK7-binding site. CaSDH SdhC is shown as surface, the bound PEs (cyan), QP, and QD sites are shown in stick form. The SdhC of E. coli QFR is shown in cartoon form. d, e Superposition of CaSDH SdhC (slate blue) with the membrane anchor of M. smegmatis Sdh2 (PDB 6LUM, light green). d Horizontal helix between the TM1 and TM2 of CaSDH SdhC (cartoon form) blocks the equivalent QD1 site in Sdh2 (surface form). e A PE molecule in CaSDH SdhC (surface form) occupies the equivalent QD2 site of Sdh2 (cartoon form). The bound menaquinone-9 (MK9, yellow) in Sdh2, and PEs (cyan) in CaSDH SdhC are shown in stick form.
