Lineage for Family f.21.2.1: Fumarate reductase respiratory complex cytochrome b subunit, FrdC

1. Root: SCOP 1.75

2. Class f: Membrane and cell surface proteins and peptides [56835] (58 folds)

3. Fold f.21: Heme-binding four-helical bundle [81344] (3 superfamilies) core: four transmembrane helices, up-and-down bundle, binds one or two heme groups in between the helices

4. Superfamily f.21.2: Fumarate reductase respiratory complex transmembrane subunits [81343] (2 families) two distinct families: in one family the common fold is contained in a single-chain subunit, in the other it is formed by two chains

5. Family f.21.2.1: Fumarate reductase respiratory complex cytochrome b subunit, FrdC [56910] (1 protein) duplication: consists of two structural repeats; the heme-binding sites are related by pseudo two fold symmetry