Fig. 4.

Comparison of the [4Fe-4S]–binding pocket in the Tma EtfX and the porcine ETF-QO. (A) The conserved coordinating residues include four [4Fe-4S]–coordinating cysteines and six largely hydrophobic supporting residues, which may tune the electric potential of the [4Fe-4S] cluster. (B) Sequence alignment. (C) Alignment of EtfCX with ETF-QO (PDB ID code 2GMH) reveals the nearly identical [4Fe-4S] coordination in EtfABCX and ETF-QO, suggesting a common electron transfer route between [4Fe-4S] and MQ or UQ. Different regions in porcine ETF-QO are colored as the corresponding regions in EtfCX.