Fold: Four-helical up-and-down bundle

core: 4 helices; bundle, closed or partly opened, left-handed twist; up-and-down

Lineage:

1. Root: scop
2. Class: All alpha proteins
3. Fold: Four-helical up-and-down bundle
   core: 4 helices; bundle, closed or partly opened, left-handed twist; up-and-down

Superfamilies:

1. Apolipoprotein (1)
2. Aspartate receptor, ligand-binding domain (1)
3. Cytochromes (2)
   Heme-containing proteins
4. Hemerythrin (1)
5. TMV-like viral coat proteins (1)
6. Acyl-CoA dehydrogenase (flavoprotein), C-terminal domain (1)
7. FKBP12-rapamycin-binding domain of FKBP-rapamycin-associated protein (FRAP) (1)
8. Proteasome activator reg(alpha) (1)
9. alpha-catenin/vinculin (1)
10. Histidine-containing phosphotransfer domain, HPT domain (2)
    contains additional, fifth helix at the N-terminus
11. Bacterial GAP domain (1)
    contains extra helices in the loops at one end of the bundle