Figure 3.

The γCA domains of Arabidopsis and Polytomella mitochondrial complex I. A and B, Position of the γCA domain on the membrane arm. Complex I (CI) is seen from the tip of the membrane arm and cut at the plane as indicated by a dashed white line in the small insets. Subunit color scheme as in Figures 1 and 2. The P_P domain of the membrane arm is shaded in blue. C and D, Cross-sections of the γCA domains of Arabidopsis (C) and Polytomella (D) at the level of the catalytic sites at the γCA/CAL subunit interfaces, as indicated by dashed circles. In Arabidopsis, one of the three possible catalytic sites coordinates a metal ion (presumably zinc; blue) and is therefore potentially active, whereas none of the three sites of the Polytomella γCA domain are occupied, and therefore they cannot be active. E and F, Details of the catalytic site regions in Arabidopsis (E) and Polytomella (F) (white boxes in C and D). Amino acids are indicated by a one-letter code. For further details, see Supplemental Figures S17–S20.