Domains of Fcc3

There are three major domains in Fcc3. One domain (blue) houses the four heme groups. The second domain (red) encloses the non-covalently bound FAD coenzyme. The final domain (green), a charged bent helix linker, connects the other two domains and is thought to control access to the active site of the enzyme (4).

A molecular graphics routine allowing maniulation of the molecule.

Figure 8. Domains of Fcc3

The energy-wire of Fcc3

The heme domain contains four heme groups separated by distances from 3.9 Å to 8 Å. The distance between the final heme and the FAD group is 7.4 Å. For efficient electron transfer, distances smaller than 8 Å are necessary. The entire distance from the first heme to the FAD is about 40 Å inside the enzyme. The hemes are covalently linked in a CxxCH motif to two cysteine residues of the enzyme. Two histidines provide the fifth and sixth ligand for the iron core of the heme and help to generate the necessary redox potential for the cofactors (4).

Figure 9. Four-heme wire of Fcc3 heme domain