Four Helix Bundle

Four helix bundles are a common structural motif or architecture that has been extensively documented. They can be observed both independently and as components of larger folding units. The motif comprises four helices packed together in a variety of different ways, forming a hydrophobic core. In the most common bundles, the helices that are adjacent in the amino acid sequence are also adjacent in the three dimensional structure, forming the so-called up-down-up-down four helix bundle. The side chains of each helix in the bundle are arranged such that the hydrophobic side chains are buried between the helices and the hydrophilic side chains are exposed on the surface of the bundle. The example shown is a transferase (CATH domain ID 1tqgA00).

References

Role of loop-helix interactions in stabilizing four-helix bundle proteins.
Chou KC, Maggiora GM, Scheraga HA
Proc Natl Acad Sci U S A89p7315-9(1992 Aug 15)
Energetics of the structure of the four-alpha-helix bundle in proteins.
Chou KC, Maggiora GM, NĂ©methy G, Scheraga HA
Proc Natl Acad Sci U S A85p4295-9(1988 Jun)
Topological distribution of four-alpha-helix bundles.
Presnell SR, Cohen FE
Proc Natl Acad Sci U S A86p6592-6(1989 Sep)
Electrostatic stabilization in four-helix bundle proteins.
Robinson CR, Sligar SG
Protein Sci2p826-37(1993 May)
Structural and functional diversity in 4-alpha-helical proteins.
Weber PC, Salemme FR
Nature287p82-4(1980 Sep 4)