Figure 3.

Topology scheme for the ChsE4-ChsE5 α₂β₂ heterotetramer and organization of ACAD domains relative to the tetramer and monomer–monomer interfaces. (a) Topology scheme for the ChsE4-ChsE5 heterotetramer. The functional heterodimers are circled in red boxes with FAD bound at the interface of ChsE4 and ChsE5; the isoalloxazine ring of FAD is highlighted in the yellow circle. (b) N-terminal domains of both ChsE4 and ChsE5 are on the surface of the tetramer; C-terminal domains of both ChsE4 and ChsE5 are at the monomer–monomer interfaces and form the core of the tetramer. Middle β-barrel domains from ChsE5 are on the surface of the tetramer, whereas middle β-barrel domains from ChsE4 are partially exposed to the solvent and the other face contacts FAD. (c) The ChsE4 and ChsE5 interface forms the functional heterodimer with an FAD bound at the interface. (d) The ChsE4 and ChsE5 interface forms a pseudoheterodimer without a bound FAD. (d) 90° rotation around the Y axis of (c).