Fig. 1: QH2 oxidation and fused SCs.
a Bifurcated electron transfer reaction conveys one electron from QH2 oxidation to the FeS protein (FeS, yellow) [2Fe-2S] cluster and another electron to cyt b (periwinkle) hemes bL and bH. Reduced [2Fe-2S] cluster transfers the electron to cyt c1 (green) heme c1 via the movement of the FeS protein from near heme bL to near heme c1. The subsequent electron transfer step from heme bH to Q from the pool is not shown for clarity. A cyt c (c2 or cy) carries electrons from heme c1 to CIV, where electrons reach the heme-Cu (Cu-b3) site, where O2 is reduced to H2O, via the CcoP (P, light blue) hemes cp1 and cp2, CcoO (O, dark green) heme co, and CcoN (N, purple) heme b. b R. capsulatus petABC encodes the structural genes of the bc1-type CIII2 subunits, the FeS protein (petA, yellow), cyt b (B, periwinkle), and cyt c1 (C, green), and ccoNOQP encodes those of the cbb3-type CIV subunits, the CcoN (ccoN, purple), CcoO (O, dark green), CcoQ (Q, gray), and CcoP (P, light blue). cycY gene (red) encodes cyt cy, and its 30-residue transmembrane helix (TMH), 69-residue linker (L), and 100-residue cyt c (cyt c) domain are indicated. Heme cofactors of b- and c-type cyts are indicated by black and white asterisks, respectively, whereas diamond and dot designate the [2Fe-2S] cluster and Cu atom, respectively. c Plasmid-borne genetic fusions. The bipartite fusion (left) is formed by in-frame linking the 3′-end of petC to the 5′-end of ccoP and the tripartite fusion (right) by adding the linker and cyt c domain of cycY to the 3′-end of ccoP. Colors and cofactors are as in a, and the his (H) and flag (F) affinity tags (dark purple) of the bipartite and tripartite fusion subunits are shown. d Schematic depiction of bipartite (left) and tripartite (right) supercomplexes (SC). The bipartite SC encodes a CIII2 dimer fused on each side to a His-tagged CIV. The tripartite SC also contains the Flag-tagged cyt domain of cy (red) at the end of CcoP (blue).
