SCOPe Funding Alert: SCOPe support from the NIH ended in April 2016. John-Marc Chandonia is the primary maintainer and has continued to develop SCOPe using vacation time. Three proposals to the NIH for continued funding have been unsuccessful. If our current NIH proposal is not funded, SCOPe will shut down permanently in Summer 2017 as Dr. Chandonia will need to seek a new position.

Lineage for Fold f.21: Heme-binding four-helical bundle

  1. Root: SCOPe 2.06
  2. 2223823Class f: Membrane and cell surface proteins and peptides [56835] (59 folds)
  3. 2226050Fold 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


  1. 2226051f.21.1: Transmembrane di-heme cytochromes [81342] (2 families) (S)
    Three of the four heme-ligands are conserved between the two families; both heme groups bind similarly but not identically
  2. 2226141f.21.2: Fumarate reductase respiratory complex transmembrane subunits [81343] (2 families) (S)
    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
  3. 2226268f.21.3: Respiratory nitrate reductase 1 gamma chain [103501] (1 family) (S)
    possible link between the two other superfamilies: this subunit corresponds to the gamma subunit of a functionally related Formate dehydrogenase N complex but is structurally closer to the Fumarate reductase subunit FrdC
    automatically mapped to Pfam PF02665

More info for Fold f.21: Heme-binding four-helical bundle

Timeline for Fold f.21: Heme-binding four-helical bundle: