Alpha Helices within Proteins

Alpha helices are one of the secondary structures found within proteins. They are generally right handed, and are stabilised by hydrogen bonding parallel to the helical axis. The side chains project outwards, and determine the interactions of the helix with neighbouring structures.

Fig 1: Alpha helix

Transmembrane domains are mostly hydrophobic, as they lie within a lipid environment.

Proline residues form kinks in the backbone and are not compatible within an alpha-helical structure.

Fig 2: Prolin

Collagen has a helical form that is very different from an alpha-helix. It has a high proportion of proline and hydroxyproline, and nearly every third residue is a glycine. The helix of collagen is more open than that of an alpha-helix and is not stabilised by hydrogen bonding within the helix. Rather, three helical strands are wound around each other to form a superhelix, with hydrogen bonds between the strands.

Fig 3: Collagen Triple Helix

Source: Fig 1, Fig 2, Fig 3.